[PATCH v32 01/12] Linux Random Number Generator

[Stephan Müller]

In an effort to provide a flexible implementation for a random number
generator that also delivers entropy during early boot time, allows
replacement of the deterministic random number generation mechanism,
implement the various components in separate code for easier
maintenance, and provide compliance to SP800-90[A|B|C], introduce
the Linux Random Number Generator (LRNG) framework.

The general design is as follows. Additional implementation details
are given in [1]. The LRNG consists of the following components:

1. The LRNG implements a DRNG. The DRNG always generates the
requested amount of output. When using the SP800-90A terminology
it operates without prediction resistance. The secondary DRNG
maintains a counter of how many bytes were generated since last
re-seed and a timer of the elapsed time since last re-seed. If either
the counter or the timer reaches a threshold, the secondary DRNG is
seeded from the entropy pool.

In case the Linux kernel detects a NUMA system, one secondary DRNG
instance per NUMA node is maintained.

2. The DRNG is seeded by concatenating the data from the
following sources:

(a) the output of the entropy pool,

(b) the Jitter RNG if available and enabled, and

(c) the CPU-based noise source such as Intel RDRAND if available and
enabled.

The entropy estimate of the data of all noise sources are added to
form the entropy estimate of the data used to seed the DRNG with.
The LRNG ensures, however, that the DRNG after seeding is at
maximum the security strength of the DRNG.

The LRNG is designed such that none of these noise sources can dominate
the other noise sources to provide seed data to the DRNG during due to
the following:

(a) During boot time, the amount of received interrupts are the trigger
points to (re)seed the DRNG.

(b) At runtime, the available entropy from the slow noise source is
concatenated with a pre-defined amount of data from the fast noise
sources. In addition, each DRNG reseed operation triggers external
noise source providers to deliver one block of data.

3. The entropy pool accumulates entropy obtained from certain events,
which will henceforth be collectively called "slow noise sources".
The entropy pool collects noise data from slow noise sources. Any data
received by the LRNG from the slow noise sources is inserted into the
entropy pool using an LFSR with a primitive and irreducible polynomial.
The following sources of entropy are used:

 (a) When an interrupt occurs, the high-resolution time stamp is mixed
into the LFSR. This time stamp is credited with heuristically implied
entropy.

 (b) HID event data like the key stroke or the mouse coordinates are
mixed into the LFSR. This data is not credited with entropy by the LRNG.

 (c) Device drivers may provide data that is mixed into the LFSR. This
data is not credited with entropy by the LRNG.

 (d) After the entropy pool is ``read'' by the DRNG, the data
used to seed the DRNG is mixed back into the entropy pool to
stir the pool. This data is not credited with entropy by the LRNG.

Any data provided from user space by either writing to /dev/random,
/dev/urandom or the IOCTL of RNDADDENTROPY on both device files
are always injected into the entropy pool.

In addition, when a hardware random number generator covered by the
Linux kernel HW generator framework wants to deliver random numbers,
it is injected into the entropy pool as well. HW generator noise source
is handled separately from the other noise source due to the fact that
the HW generator framework may decide by itself when to deliver data
whereas the other noise sources always requested for data driven by the
LRNG operation. Similarly any user space provided data is inserted into
the entropy pool.

When the DRNG requires data from the entropy pool, the entire
entropy pool is processed with an SP800-90A section 10.3.1 compliant
hash_df function to generate random numbers.

To speed up the interrupt handling code of the LRNG, the time stamp
collected for an interrupt event is truncated to the 8 least
significant bits. 64 truncated time stamps are concatenated and then
jointly inserted into the LFSR. During boot time, until the fully seeded
stage is reached, each time stamp with its 32 least significant bits is
inserted into the LFSR at the time of arrival.

The LRNG allows the DRNG mechanism to be changed at runtime. Per default,
a ChaCha20-based DRNG is used. The ChaCha20-DRNG implemented for the
LRNG is also provided as a stand-alone user space deterministic random
number generator. The LRNG also offers an SP800-90A DRBG based on the
Linux kernel crypto API DRBG implementation.

The processing of entropic data from the noise source before injecting
them into the DRNG is performed with the following mathematical
operations:

1. LFSR: The 8 least significant bits of the time stamp data received
from the interrupts are processed with an LFSR. That LFSR is implemented
identically to the LSFR used in the existing /dev/random implementation
except that it is capable of processing an entire word and that a
different polynomial is used. The reason for the different polynomial
is performance in a performance sensitive code section, the interrupt
handler. The chosen polynomials have 4 taps. Also, this LFSR-approach
is used in the OpenBSD /dev/random equivalent.

2. Concatenation: The temporary seed buffer used to seed the DRNG is
a concatenation of parts of the entropy pool data, and the CPU noise
source output.

The DRNG always tries to seed itself with 256 bits of entropy, except
during boot. In any case, if the noise sources cannot deliver that
amount, the available entropy is used and the DRNG keeps track on how
much entropy it was seeded with. The entropy implied by the LRNG
available in the entropy pool may be too conservative. To ensure
that during boot time all available entropy from the entropy pool is
transferred to the DRNG, the hash_df function always generates 256
data bits during boot to seed the DRNG. During boot, the DRNG is
seeded as follows:

1. The DRNG is reseeded from the entropy pool and potentially the fast
noise sources if the entropy pool has collected at least 32 bits of
entropy from the interrupt noise source. The goal of this step is to
ensure that the DRNG receives some initial entropy as early as
possible. In addition it receives the entropy available from
the fast noise sources.

2. The DRNG is reseeded from the entropy pool and potentially the fast
noise sources if all noise sources collectively can provide at least
128 bits of entropy.

3. The DRNG is reseeded from the entropy pool and potentially the fast
noise sources if all noise sources collectivel can provide at least 256
bits.

At the time of the reseeding steps, the DRNG requests as much entropy as
is available in order to skip certain steps and reach the seeding level
of 256 bits. This may imply that one or more of the aforementioned steps
are skipped.

In all listed steps, the DRNG is (re)seeded with a number of random
bytes from the entropy pool that is at most the amount of entropy
present in the entropy pool. This means that when the entropy pool
contains 128 or 256 bits of entropy, the DRNG is seeded with that
amount of entropy as well.

Before the DRNG is seeded with 256 bits of entropy in step 3,
requests of random data from /dev/random are not processed.

The hash_df operation providing random data from the entropy pool will
always require that all entropy sources collectively can deliver at
least 129 entropy bits as configured with (128 bits of entropy for
seeding plus one bit of entropy that is lost with the post
processing as defined in SP800-90B).

The DRNG operates as deterministic random number generator with the
following properties:

* The maximum number of random bytes that can be generated with one
DRNG generate operation is limited to 4096 bytes. When longer random
numbers are requested, multiple DRNG generate operations are performed.
The ChaCha20 DRNG as well as the SP800-90A DRBGs implement an update of
their state after completing a generate request for backtracking
resistance.

* The secondary DRNG is reseeded with whatever entropy is available –
in the worst case where no additional entropy can be provided by the
noise sources, the DRNG is not re-seeded and continues its operation
to try to reseed again after again the expiry of one of these thresholds:

 - If the last reseeding of the secondary DRNG is more than 600 seconds
   ago, or

 - 2^20 DRNG generate operations are performed, whatever comes first, or

 - the secondary DRNG is forced to reseed before the next generation of
   random numbers if data has been injected into the LRNG by writing data
   into /dev/random or /dev/urandom.

The chosen values prevent high-volume requests from user space to cause
frequent reseeding operations which drag down the performance of the
DRNG.

With the automatic reseeding after 600 seconds, the LRNG is triggered
to reseed itself before the first request after a suspend that put the
hardware to sleep for longer than 600 seconds.

The LRNG uses the following runtime memory using the currently
smallest configuration:

* 576 bytes (512 bytes for the entropy pool and 64 for the entropy pool
  meta data) for the entropy pool management

* 64 bytes per CPU for the time stamp array

To support smaller devices including IoT environments, this patch
allows reducing the runtime memory footprint of the LRNG at compile
time by selecting smaller entropy pool sizes.

The entropy pool has support for sizes of 256, 128 and 64 bytes supported
by primitive and irreducible polynomials.

The time stamp array is reduced to one atomic_t variable per CPU, i.e.
4 bytes when CONFIG_BASE_SMALL is selected during kernel
configuration. This implies that after the receipt of 4 interrupts on
one CPU, the data is injected into the LFSR. Depending on the behavior
of the CPU caches, this may imply that the average interrupt handler
execution time increases a bit, since instead of injecting 8 atomic_t
values at one given time into the LFSR, only one is processed which
may incur cache misses.

When selecting the compilation of a kernel for a small environment,
prevent the allocation of a buffer up to 4096 bytes to serve user space
requests. In this case, the stack variable of 64 bytes is used to serve
all user space requests.

The LRNG has the following properties:

* internal noise source: interrupts timing with fast boot time seeding

* high performance of interrupt handling code: The LRNG impact on the
interrupt handling has been reduced to a minimum. On one example
system, the LRNG interrupt handling code executes within an average
of 65 cycles whereas the existing /dev/random on the same device
takes about 97 cycles when measuring the execution time of
add_interrupt_randomness().

* lockless LFSR to collect raw entropy supporing concurrency-free
  use of massive parallel systems

* use of standalone ChaCha20 based RNG with the option to use a
  different DRNG selectable at compile time

* "atomic" seeding of secondary DRBG to ensure full entropy transport

* instantiate one DRNG per NUMA node

* support for runtime switchable output DRNGs

* use of only well-defined entropy-preserving operations to collect,
compress and forward entropy: concatenation, LFSR, SP800-90A hash_df
function

* compile-time selectable entropy pool size: the choice also
uses the applicable LFSR polynomial to maintain the entropy pool
size

* support of small systems by allowing the reduction of the
runtime memory needs

Further details including the rationale for the design choices and
properties of the LRNG together with testing is provided at [1].
In addition, the documentation explains the conducted regression
tests to verify that the LRNG is API and ABI compatible with the
existing /dev/random implementation.

[1] https://www.chronox.de/lrng.html

CC: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
CC: "Alexander E. Patrakov" <patrakov@xxxxxxxxx>
CC: "Ahmed S. Darwish" <darwish.07@xxxxxxxxx>
CC: "Theodore Y. Ts'o" <tytso@xxxxxxx>
CC: Willy Tarreau <w@xxxxxx>
CC: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
CC: Vito Caputo <vcaputo@xxxxxxxxxxx>
CC: Andreas Dilger <adilger.kernel@xxxxxxxxx>
CC: Jan Kara <jack@xxxxxxx>
CC: Ray Strode <rstrode@xxxxxxxxxx>
CC: William Jon McCann <mccann@xxxxxxx>
CC: zhangjs <zachary@xxxxxxxxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxx>
CC: Florian Weimer <fweimer@xxxxxxxxxx>
CC: Lennart Poettering <mzxreary@xxxxxxxxxxx>
CC: Nicolai Stange <nstange@xxxxxxx>
Mathematical aspects Reviewed-by: "Peter, Matthias" <matthias.peter@xxxxxxxxxxx>
Reviewed-by: Marcelo Henrique Cerri <marcelo.cerri@xxxxxxxxxxxxx>
Reviewed-by: Roman Drahtmueller <draht@xxxxxxxxxxxxxx>
Tested-by: Roman Drahtmüller <draht@xxxxxxxxxxxxxx>
Tested-by: Marcelo Henrique Cerri <marcelo.cerri@xxxxxxxxxxxxx>
Tested-by: Neil Horman <nhorman@xxxxxxxxxx>
Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
---
 MAINTAINERS                         |   7 +
 drivers/char/Kconfig                |   2 +
 drivers/char/Makefile               |   9 +-
 drivers/char/lrng/Kconfig           |  68 +++
 drivers/char/lrng/Makefile          |   9 +
 drivers/char/lrng/lrng_archrandom.c |  93 ++++
 drivers/char/lrng/lrng_aux.c        | 136 ++++++
 drivers/char/lrng/lrng_chacha20.c   | 320 ++++++++++++++
 drivers/char/lrng/lrng_chacha20.h   |  29 ++
 drivers/char/lrng/lrng_drng.c       | 409 ++++++++++++++++++
 drivers/char/lrng/lrng_interfaces.c | 648 ++++++++++++++++++++++++++++
 drivers/char/lrng/lrng_internal.h   | 333 ++++++++++++++
 drivers/char/lrng/lrng_lfsr.h       | 152 +++++++
 drivers/char/lrng/lrng_pool.c       | 589 +++++++++++++++++++++++++
 drivers/char/lrng/lrng_sw_noise.c   | 155 +++++++
 drivers/char/lrng/lrng_sw_noise.h   |  57 +++
 include/linux/lrng.h                |  63 +++
 17 files changed, 3078 insertions(+), 1 deletion(-)
 create mode 100644 drivers/char/lrng/Kconfig
 create mode 100644 drivers/char/lrng/Makefile
 create mode 100644 drivers/char/lrng/lrng_archrandom.c
 create mode 100644 drivers/char/lrng/lrng_aux.c
 create mode 100644 drivers/char/lrng/lrng_chacha20.c
 create mode 100644 drivers/char/lrng/lrng_chacha20.h
 create mode 100644 drivers/char/lrng/lrng_drng.c
 create mode 100644 drivers/char/lrng/lrng_interfaces.c
 create mode 100644 drivers/char/lrng/lrng_internal.h
 create mode 100644 drivers/char/lrng/lrng_lfsr.h
 create mode 100644 drivers/char/lrng/lrng_pool.c
 create mode 100644 drivers/char/lrng/lrng_sw_noise.c
 create mode 100644 drivers/char/lrng/lrng_sw_noise.h
 create mode 100644 include/linux/lrng.h

diff --git a/MAINTAINERS b/MAINTAINERS
index deaafb617361..74f6fd1ba1ec 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10084,6 +10084,13 @@ F:	Documentation/litmus-tests/
 F:	Documentation/memory-barriers.txt
 F:	tools/memory-model/
 
+LINUX RANDOM NUMBER GENERATOR (LRNG) DRIVER
+M:	Stephan Mueller <smueller@xxxxxxxxxx>
+S:	Maintained
+W:	https://www.chronox.de/lrng.html
+F:	drivers/char/lrng/*
+F:	include/linux/lrng.h
+
 LIS3LV02D ACCELEROMETER DRIVER
 M:	Eric Piel <eric.piel@xxxxxxxxxxxxxxxx>
 S:	Maintained
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index b1bd336761b1..8a5b8a2db2c7 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -470,6 +470,8 @@ config ADI
 	  and SSM (Silicon Secured Memory).  Intended consumers of this
 	  driver include crash and makedumpfile.
 
+source "drivers/char/lrng/Kconfig"
+
 endmenu
 
 config RANDOM_TRUST_CPU
diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index ffce287ef415..2110d3e28cf2 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -3,7 +3,14 @@
 # Makefile for the kernel character device drivers.
 #
 
-obj-y				+= mem.o random.o
+obj-y				+= mem.o
+
+ifeq ($(CONFIG_LRNG),y)
+  obj-y				+= lrng/
+else
+  obj-y				+= random.o
+endif
+
 obj-$(CONFIG_TTY_PRINTK)	+= ttyprintk.o
 obj-y				+= misc.o
 obj-$(CONFIG_ATARI_DSP56K)	+= dsp56k.o
diff --git a/drivers/char/lrng/Kconfig b/drivers/char/lrng/Kconfig
new file mode 100644
index 000000000000..059b21d9728c
--- /dev/null
+++ b/drivers/char/lrng/Kconfig
@@ -0,0 +1,68 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Linux Random Number Generator configuration
+#
+
+menuconfig LRNG
+	bool "Linux Random Number Generator"
+	select CRYPTO_LIB_SHA256 if CRYPTO
+	help
+	  The Linux Random Number Generator (LRNG) is the replacement
+	  of the existing /dev/random provided with drivers/char/random.c.
+	  It generates entropy from different noise sources and
+	  delivers significant entropy during boot.
+
+if LRNG
+
+choice
+	prompt "LRNG Entropy Pool Size"
+	default LRNG_POOL_SIZE_4096
+	help
+	  Select the size of the LRNG entropy pool. The size of the
+	  entropy pool is relevant for the amount of entropy that
+	  the LRNG can maintain as a maximum. The larger the size
+	  of the entropy pool is the more entropy can be maintained
+	  but the less often older entropic values are overwritten
+	  with new entropy.
+
+	config LRNG_POOL_SIZE_512
+		bool "512 bits"
+
+	config LRNG_POOL_SIZE_1024
+		bool "1024 bits"
+
+	config LRNG_POOL_SIZE_2048
+		bool "2048 bits"
+
+	config LRNG_POOL_SIZE_4096
+		bool "4096 bits (default)"
+
+	config LRNG_POOL_SIZE_8192
+		bool "8192 bits"
+
+	config LRNG_POOL_SIZE_16384
+		bool "16384 bits"
+
+	config LRNG_POOL_SIZE_32768
+		bool "32768 bits"
+
+	config LRNG_POOL_SIZE_65536
+		bool "65536 bits"
+
+	config LRNG_POOL_SIZE_131072
+		bool "131072 bits"
+endchoice
+
+config LRNG_POOL_SIZE
+	int
+	default 0 if LRNG_POOL_SIZE_512
+	default 1 if LRNG_POOL_SIZE_1024
+	default 2 if LRNG_POOL_SIZE_2048
+	default 3 if LRNG_POOL_SIZE_4096
+	default 4 if LRNG_POOL_SIZE_8192
+	default 5 if LRNG_POOL_SIZE_16384
+	default 6 if LRNG_POOL_SIZE_32768
+	default 7 if LRNG_POOL_SIZE_65536
+	default 8 if LRNG_POOL_SIZE_131072
+
+endif # LRNG
diff --git a/drivers/char/lrng/Makefile b/drivers/char/lrng/Makefile
new file mode 100644
index 000000000000..1d2a0211973d
--- /dev/null
+++ b/drivers/char/lrng/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the Linux Random Number Generator.
+#
+
+obj-y				+= lrng_pool.o lrng_aux.o \
+				   lrng_sw_noise.o lrng_archrandom.o \
+				   lrng_drng.o lrng_chacha20.o \
+				   lrng_interfaces.o \
diff --git a/drivers/char/lrng/lrng_archrandom.c b/drivers/char/lrng/lrng_archrandom.c
new file mode 100644
index 000000000000..5e81c4e856d5
--- /dev/null
+++ b/drivers/char/lrng/lrng_archrandom.c
@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG Fast Noise Source: CPU-based noise source
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/random.h>
+
+#include "lrng_internal.h"
+
+/*
+ * Estimated entropy of data is a 32th of LRNG_DRNG_SECURITY_STRENGTH_BITS.
+ * As we have no ability to review the implementation of those noise sources,
+ * it is prudent to have a conservative estimate here.
+ */
+#define LRNG_ARCHRANDOM_DEFAULT_STRENGTH (LRNG_DRNG_SECURITY_STRENGTH_BITS>>5)
+#define LRNG_ARCHRANDOM_TRUST_CPU_STRENGTH LRNG_DRNG_SECURITY_STRENGTH_BITS
+#ifdef CONFIG_RANDOM_TRUST_CPU
+static u32 archrandom = LRNG_ARCHRANDOM_TRUST_CPU_STRENGTH;
+#else
+static u32 archrandom = LRNG_ARCHRANDOM_DEFAULT_STRENGTH;
+#endif
+module_param(archrandom, uint, 0644);
+MODULE_PARM_DESC(archrandom, "Entropy in bits of 256 data bits from CPU noise source (e.g. RDRAND)");
+
+static int __init lrng_parse_trust_cpu(char *arg)
+{
+	int ret;
+	bool trust_cpu = false;
+
+	ret = kstrtobool(arg, &trust_cpu);
+	if (ret)
+		return ret;
+
+	if (trust_cpu)
+		archrandom = LRNG_ARCHRANDOM_TRUST_CPU_STRENGTH;
+	else
+		archrandom = LRNG_ARCHRANDOM_DEFAULT_STRENGTH;
+
+	return 0;
+}
+early_param("random.trust_cpu", lrng_parse_trust_cpu);
+
+/**
+ * lrng_get_arch() - Get CPU noise source entropy
+ *
+ * @outbuf: buffer to store entropy of size LRNG_DRNG_SECURITY_STRENGTH_BYTES
+ *
+ * Return:
+ * * > 0 on success where value provides the added entropy in bits
+ * *   0 if no fast source was available
+ */
+u32 lrng_get_arch(u8 *outbuf)
+{
+	u32 i, ent_bits = archrandom;
+
+	/* operate on full blocks */
+	BUILD_BUG_ON(LRNG_DRNG_SECURITY_STRENGTH_BYTES % sizeof(unsigned long));
+	/* ensure we have aligned buffers */
+	BUILD_BUG_ON(LRNG_KCAPI_ALIGN % sizeof(unsigned long));
+
+	if (!ent_bits)
+		return 0;
+
+	for (i = 0; i < LRNG_DRNG_SECURITY_STRENGTH_BYTES;
+	     i += sizeof(unsigned long)) {
+		if (!arch_get_random_seed_long((unsigned long *)(outbuf + i)) &&
+		    !arch_get_random_long((unsigned long *)(outbuf + i))) {
+			archrandom = 0;
+			return 0;
+		}
+	}
+
+	/* Obtain entropy statement -- cap entropy to buffer size in bits */
+	ent_bits = min_t(u32, ent_bits, LRNG_DRNG_SECURITY_STRENGTH_BITS);
+	pr_debug("obtained %u bits of entropy from CPU RNG noise source\n",
+		 ent_bits);
+	return ent_bits;
+}
+
+u32 lrng_slow_noise_req_entropy(u32 required_entropy_bits)
+{
+	u32 arch_ent_bits = min_t(u32, archrandom,
+				  LRNG_DRNG_SECURITY_STRENGTH_BITS);
+	u32 fast_noise_entropy = arch_ent_bits + lrng_jent_entropylevel();
+
+	if (fast_noise_entropy > required_entropy_bits)
+		return 0;
+	return (required_entropy_bits - fast_noise_entropy);
+}
diff --git a/drivers/char/lrng/lrng_aux.c b/drivers/char/lrng/lrng_aux.c
new file mode 100644
index 000000000000..9f46c5707517
--- /dev/null
+++ b/drivers/char/lrng/lrng_aux.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG auxiliary interfaces
+ *
+ * Copyright (C) 2019 Stephan Mueller <smueller@xxxxxxxxxx>
+ * Copyright (C) 2017 Jason A. Donenfeld <Jason@xxxxxxxxx>. All
+ * Rights Reserved.
+ * Copyright (C) 2016 Jason Cooper <jason@xxxxxxxxxxxxxx>
+ */
+
+#include <linux/mm.h>
+#include <linux/random.h>
+
+#include "lrng_internal.h"
+
+struct batched_entropy {
+	union {
+		u64 entropy_u64[LRNG_DRNG_BLOCKSIZE / sizeof(u64)];
+		u32 entropy_u32[LRNG_DRNG_BLOCKSIZE / sizeof(u32)];
+	};
+	unsigned int position;
+	spinlock_t batch_lock;
+};
+
+/*
+ * Get a random word for internal kernel use only. The quality of the random
+ * number is as good as /dev/urandom, but there is no backtrack protection,
+ * with the goal of being quite fast and not depleting entropy.
+ */
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
+	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
+};
+
+u64 get_random_u64(void)
+{
+	u64 ret;
+	unsigned long flags;
+	struct batched_entropy *batch;
+
+	lrng_debug_report_seedlevel("get_random_u64");
+
+	batch = raw_cpu_ptr(&batched_entropy_u64);
+	spin_lock_irqsave(&batch->batch_lock, flags);
+	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
+		lrng_drng_get_atomic((u8 *)batch->entropy_u64,
+				      LRNG_DRNG_BLOCKSIZE);
+		batch->position = 0;
+	}
+	ret = batch->entropy_u64[batch->position++];
+	spin_unlock_irqrestore(&batch->batch_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(get_random_u64);
+
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
+	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
+};
+
+u32 get_random_u32(void)
+{
+	u32 ret;
+	unsigned long flags;
+	struct batched_entropy *batch;
+
+	lrng_debug_report_seedlevel("get_random_u32");
+
+	batch = raw_cpu_ptr(&batched_entropy_u32);
+	spin_lock_irqsave(&batch->batch_lock, flags);
+	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
+		lrng_drng_get_atomic((u8 *)batch->entropy_u32,
+				      LRNG_DRNG_BLOCKSIZE);
+		batch->position = 0;
+	}
+	ret = batch->entropy_u32[batch->position++];
+	spin_unlock_irqrestore(&batch->batch_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(get_random_u32);
+
+/*
+ * It's important to invalidate all potential batched entropy that might
+ * be stored before the crng is initialized, which we can do lazily by
+ * simply resetting the counter to zero so that it's re-extracted on the
+ * next usage.
+ */
+void invalidate_batched_entropy(void)
+{
+	int cpu;
+	unsigned long flags;
+
+	for_each_possible_cpu(cpu) {
+		struct batched_entropy *batched_entropy;
+
+		batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
+		spin_lock_irqsave(&batched_entropy->batch_lock, flags);
+		batched_entropy->position = 0;
+		spin_unlock(&batched_entropy->batch_lock);
+
+		batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
+		spin_lock(&batched_entropy->batch_lock);
+		batched_entropy->position = 0;
+		spin_unlock_irqrestore(&batched_entropy->batch_lock, flags);
+	}
+}
+
+/**
+ * randomize_page - Generate a random, page aligned address
+ * @start:	The smallest acceptable address the caller will take.
+ * @range:	The size of the area, starting at @start, within which the
+ *		random address must fall.
+ *
+ * If @start + @range would overflow, @range is capped.
+ *
+ * NOTE: Historical use of randomize_range, which this replaces, presumed that
+ * @start was already page aligned.  We now align it regardless.
+ *
+ * Return: A page aligned address within [start, start + range).  On error,
+ * @start is returned.
+ */
+unsigned long randomize_page(unsigned long start, unsigned long range)
+{
+	if (!PAGE_ALIGNED(start)) {
+		range -= PAGE_ALIGN(start) - start;
+		start = PAGE_ALIGN(start);
+	}
+
+	if (start > ULONG_MAX - range)
+		range = ULONG_MAX - start;
+
+	range >>= PAGE_SHIFT;
+
+	if (range == 0)
+		return start;
+
+	return start + (get_random_long() % range << PAGE_SHIFT);
+}
diff --git a/drivers/char/lrng/lrng_chacha20.c b/drivers/char/lrng/lrng_chacha20.c
new file mode 100644
index 000000000000..9da139d89959
--- /dev/null
+++ b/drivers/char/lrng/lrng_chacha20.c
@@ -0,0 +1,320 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * Backend for the LRNG providing the cryptographic primitives using
+ * ChaCha20 cipher implementations.
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <crypto/chacha.h>
+#include <crypto/sha.h>
+#include <linux/lrng.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+
+#include "lrng_chacha20.h"
+#include "lrng_internal.h"
+
+/******************************* ChaCha20 DRNG *******************************/
+
+#define CHACHA_BLOCK_WORDS	(CHACHA_BLOCK_SIZE / sizeof(u32))
+
+struct chacha20_state {
+	struct chacha20_block block;
+};
+
+/*
+ * Have a static memory blocks for the ChaCha20 DRNG instance to avoid calling
+ * kmalloc too early in the boot cycle. For subsequent allocation requests,
+ * such as per-NUMA-node DRNG instances, kmalloc will be used.
+ */
+struct chacha20_state chacha20;
+
+/**
+ * Update of the ChaCha20 state by either using an unused buffer part or by
+ * generating one ChaCha20 block which is half of the state of the ChaCha20.
+ * The block is XORed into the key part of the state. This shall ensure
+ * backtracking resistance as well as a proper mix of the ChaCha20 state once
+ * the key is injected.
+ */
+static void lrng_chacha20_update(struct chacha20_state *chacha20_state,
+				 u32 *buf, u32 used_words)
+{
+	struct chacha20_block *chacha20 = &chacha20_state->block;
+	u32 i, tmp[CHACHA_BLOCK_WORDS];
+
+	BUILD_BUG_ON(sizeof(struct chacha20_block) != CHACHA_BLOCK_SIZE);
+	BUILD_BUG_ON(CHACHA_BLOCK_SIZE != 2 * CHACHA_KEY_SIZE);
+
+	if (used_words > CHACHA_KEY_SIZE_WORDS) {
+		chacha20_block(&chacha20->constants[0], (u8 *)tmp);
+		for (i = 0; i < CHACHA_KEY_SIZE_WORDS; i++)
+			chacha20->key.u[i] ^= le32_to_cpu(tmp[i]);
+		memzero_explicit(tmp, sizeof(tmp));
+	} else {
+		for (i = 0; i < CHACHA_KEY_SIZE_WORDS; i++)
+			chacha20->key.u[i] ^= le32_to_cpu(buf[i + used_words]);
+	}
+
+	/* Deterministic increment of nonce as required in RFC 7539 chapter 4 */
+	chacha20->nonce[0]++;
+	if (chacha20->nonce[0] == 0)
+		chacha20->nonce[1]++;
+	if (chacha20->nonce[1] == 0)
+		chacha20->nonce[2]++;
+
+	/* Leave counter untouched as it is start value is undefined in RFC */
+}
+
+/*
+ * Seed the ChaCha20 DRNG by injecting the input data into the key part of
+ * the ChaCha20 state. If the input data is longer than the ChaCha20 key size,
+ * perform a ChaCha20 operation after processing of key size input data.
+ * This operation shall spread out the entropy into the ChaCha20 state before
+ * new entropy is injected into the key part.
+ */
+static int lrng_cc20_drng_seed_helper(void *drng, const u8 *inbuf, u32 inbuflen)
+{
+	struct chacha20_state *chacha20_state = (struct chacha20_state *)drng;
+	struct chacha20_block *chacha20 = &chacha20_state->block;
+
+	while (inbuflen) {
+		u32 i, todo = min_t(u32, inbuflen, CHACHA_KEY_SIZE);
+
+		for (i = 0; i < todo; i++)
+			chacha20->key.b[i] ^= inbuf[i];
+
+		/* Break potential dependencies between the inbuf key blocks */
+		lrng_chacha20_update(chacha20_state, NULL,
+				     CHACHA_BLOCK_WORDS);
+		inbuf += todo;
+		inbuflen -= todo;
+	}
+
+	return 0;
+}
+
+/*
+ * Chacha20 DRNG generation of random numbers: the stream output of ChaCha20
+ * is the random number. After the completion of the generation of the
+ * stream, the entire ChaCha20 state is updated.
+ *
+ * Note, as the ChaCha20 implements a 32 bit counter, we must ensure
+ * that this function is only invoked for at most 2^32 - 1 ChaCha20 blocks
+ * before a reseed or an update happens. This is ensured by the variable
+ * outbuflen which is a 32 bit integer defining the number of bytes to be
+ * generated by the ChaCha20 DRNG. At the end of this function, an update
+ * operation is invoked which implies that the 32 bit counter will never be
+ * overflown in this implementation.
+ */
+static int lrng_cc20_drng_generate_helper(void *drng, u8 *outbuf, u32 outbuflen)
+{
+	struct chacha20_state *chacha20_state = (struct chacha20_state *)drng;
+	struct chacha20_block *chacha20 = &chacha20_state->block;
+	u32 aligned_buf[CHACHA_BLOCK_WORDS], ret = outbuflen,
+	    used = CHACHA_BLOCK_WORDS;
+	int zeroize_buf = 0;
+
+	while (outbuflen >= CHACHA_BLOCK_SIZE) {
+		chacha20_block(&chacha20->constants[0], outbuf);
+		outbuf += CHACHA_BLOCK_SIZE;
+		outbuflen -= CHACHA_BLOCK_SIZE;
+	}
+
+	if (outbuflen) {
+		chacha20_block(&chacha20->constants[0], (u8 *)aligned_buf);
+		memcpy(outbuf, aligned_buf, outbuflen);
+		used = ((outbuflen + sizeof(aligned_buf[0]) - 1) /
+			sizeof(aligned_buf[0]));
+		zeroize_buf = 1;
+	}
+
+	lrng_chacha20_update(chacha20_state, aligned_buf, used);
+
+	if (zeroize_buf)
+		memzero_explicit(aligned_buf, sizeof(aligned_buf));
+
+	return ret;
+}
+
+void lrng_cc20_init_state(struct chacha20_state *state)
+{
+	struct chacha20_block *chacha20 = &state->block;
+	unsigned long v;
+	u32 i;
+
+	lrng_cc20_init_rfc7539(chacha20);
+
+	for (i = 0; i < CHACHA_KEY_SIZE_WORDS; i++) {
+		chacha20->key.u[i] ^= jiffies;
+		chacha20->key.u[i] ^= random_get_entropy();
+		if (arch_get_random_seed_long(&v) || arch_get_random_long(&v))
+			chacha20->key.u[i] ^= v;
+	}
+
+	for (i = 0; i < 3; i++) {
+		chacha20->nonce[i] ^= jiffies;
+		chacha20->nonce[i] ^= random_get_entropy();
+		if (arch_get_random_seed_long(&v) || arch_get_random_long(&v))
+			chacha20->nonce[i] ^= v;
+	}
+
+	lrng_chacha20_update(state, NULL, CHACHA_BLOCK_WORDS);
+	pr_info("ChaCha20 core initialized\n");
+}
+
+void __init lrng_cc20_init_state_boot(struct chacha20_state *state)
+{
+	struct chacha20_block *chacha20 = &state->block;
+	unsigned long v;
+	u32 i;
+
+	for (i = 0; i < CHACHA_KEY_SIZE_WORDS; i++) {
+		if (arch_get_random_seed_long_early(&v) ||
+		    arch_get_random_long_early(&v))
+			chacha20->key.u[i] ^= v;
+	}
+
+	for (i = 0; i < 3; i++) {
+		if (arch_get_random_seed_long_early(&v) ||
+		    arch_get_random_long_early(&v))
+			chacha20->nonce[i] ^= v;
+	}
+
+	lrng_chacha20_update(state, NULL, CHACHA_BLOCK_WORDS);
+}
+
+/*
+ * Allocation of the DRNG state
+ */
+static void *lrng_cc20_drng_alloc(u32 sec_strength)
+{
+	struct chacha20_state *state = NULL;
+
+	if (sec_strength > CHACHA_KEY_SIZE) {
+		pr_err("Security strength of ChaCha20 DRNG (%u bits) lower than requested by LRNG (%u bits)\n",
+			CHACHA_KEY_SIZE * 8, sec_strength * 8);
+		return ERR_PTR(-EINVAL);
+	}
+	if (sec_strength < CHACHA_KEY_SIZE)
+		pr_warn("Security strength of ChaCha20 DRNG (%u bits) higher than requested by LRNG (%u bits)\n",
+			CHACHA_KEY_SIZE * 8, sec_strength * 8);
+
+	state = kmalloc(sizeof(struct chacha20_state), GFP_KERNEL);
+	if (!state)
+		return ERR_PTR(-ENOMEM);
+	pr_debug("memory for ChaCha20 core allocated\n");
+
+	lrng_cc20_init_state(state);
+
+	return state;
+}
+
+static void lrng_cc20_drng_dealloc(void *drng)
+{
+	struct chacha20_state *chacha20_state = (struct chacha20_state *)drng;
+
+	if (drng == &chacha20) {
+		memzero_explicit(chacha20_state, sizeof(*chacha20_state));
+		pr_debug("static ChaCha20 core zeroized\n");
+		return;
+	}
+
+	pr_debug("ChaCha20 core zeroized and freed\n");
+	kzfree(chacha20_state);
+}
+
+/******************************* Hash Operation *******************************/
+
+#ifdef CONFIG_CRYPTO_LIB_SHA256
+
+static u32 lrng_cc20_hash_digestsize(void *hash)
+{
+	return SHA256_DIGEST_SIZE;
+}
+
+static int lrng_cc20_hash_buffer(void *hash, const u8 *inbuf, u32 inbuflen,
+				 u8 *digest)
+{
+	struct sha256_state sctx;
+
+	sha256_init(&sctx);
+	sha256_update(&sctx, inbuf, inbuflen);
+	sha256_final(&sctx, digest);
+
+	/* Zeroization of sctx is performed by sha256_final */
+
+	return 0;
+}
+
+static const char *lrng_cc20_hash_name(void)
+{
+	const char *cc20_hash_name = "SHA-256";
+	return cc20_hash_name;
+}
+
+#else /* CONFIG_CRYPTO_LIB_SHA256 */
+
+/*
+ * If the SHA-256 support is not compiled, we fall back to SHA-1 that is always
+ * compiled and present in the kernel.
+ */
+static u32 lrng_cc20_hash_digestsize(void *hash)
+{
+	return (SHA1_DIGEST_WORDS * sizeof(u32));
+}
+
+static int lrng_cc20_hash_buffer(void *hash, const u8 *inbuf, u32 inbuflen,
+				 u8 *digest)
+{
+	u32 i;
+	u32 workspace[SHA1_WORKSPACE_WORDS];
+
+	WARN_ON(inbuflen % (SHA1_WORKSPACE_WORDS * sizeof(u32)));
+
+	sha1_init((u32 *)digest);
+	for (i = 0; i < inbuflen; i += (SHA1_WORKSPACE_WORDS * sizeof(u32)))
+		sha1_transform((u32 *)digest, (inbuf + i), workspace);
+	memzero_explicit(workspace, sizeof(workspace));
+
+	return 0;
+}
+
+static const char *lrng_cc20_hash_name(void)
+{
+	const char *cc20_hash_name = "SHA-1";
+	return cc20_hash_name;
+}
+
+#endif /* CONFIG_CRYPTO_LIB_SHA256 */
+
+static void *lrng_cc20_hash_alloc(const u8 *key, u32 keylen)
+{
+	pr_info("Hash %s allocated\n", lrng_cc20_hash_name());
+	return NULL;
+}
+
+static void lrng_cc20_hash_dealloc(void *hash)
+{
+}
+
+static const char *lrng_cc20_drng_name(void)
+{
+	const char *cc20_drng_name = "ChaCha20 DRNG";
+	return cc20_drng_name;
+}
+
+const struct lrng_crypto_cb lrng_cc20_crypto_cb = {
+	.lrng_drng_name			= lrng_cc20_drng_name,
+	.lrng_hash_name			= lrng_cc20_hash_name,
+	.lrng_drng_alloc		= lrng_cc20_drng_alloc,
+	.lrng_drng_dealloc		= lrng_cc20_drng_dealloc,
+	.lrng_drng_seed_helper		= lrng_cc20_drng_seed_helper,
+	.lrng_drng_generate_helper	= lrng_cc20_drng_generate_helper,
+	.lrng_hash_alloc		= lrng_cc20_hash_alloc,
+	.lrng_hash_dealloc		= lrng_cc20_hash_dealloc,
+	.lrng_hash_digestsize		= lrng_cc20_hash_digestsize,
+	.lrng_hash_buffer		= lrng_cc20_hash_buffer,
+};
diff --git a/drivers/char/lrng/lrng_chacha20.h b/drivers/char/lrng/lrng_chacha20.h
new file mode 100644
index 000000000000..1533b2490964
--- /dev/null
+++ b/drivers/char/lrng/lrng_chacha20.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * LRNG ChaCha20 definitions
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#include <crypto/chacha.h>
+
+/* State according to RFC 7539 section 2.3 */
+struct chacha20_block {
+	u32 constants[4];
+	union {
+#define CHACHA_KEY_SIZE_WORDS (CHACHA_KEY_SIZE / sizeof(u32))
+		u32 u[CHACHA_KEY_SIZE_WORDS];
+		u8  b[CHACHA_KEY_SIZE];
+	} key __latent_entropy;
+	u32 counter;
+	u32 nonce[3] __latent_entropy;
+};
+
+static inline void lrng_cc20_init_rfc7539(struct chacha20_block *chacha20)
+{
+	/* String "expand 32-byte k" */
+	chacha20->constants[0] = 0x61707865;
+	chacha20->constants[1] = 0x3320646e;
+	chacha20->constants[2] = 0x79622d32;
+	chacha20->constants[3] = 0x6b206574;
+}
diff --git a/drivers/char/lrng/lrng_drng.c b/drivers/char/lrng/lrng_drng.c
new file mode 100644
index 000000000000..ac6e40794cfe
--- /dev/null
+++ b/drivers/char/lrng/lrng_drng.c
@@ -0,0 +1,409 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG DRNG processing
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/lrng.h>
+
+#include "lrng_internal.h"
+
+/*
+ * Maximum number of seconds between DRNG reseed intervals of the DRNG. Note,
+ * this is enforced with the next request of random numbers from the
+ * DRNG. Setting this value to zero implies a reseeding attempt before every
+ * generated random number.
+ */
+int lrng_drng_reseed_max_time = 600;
+
+static atomic_t lrng_avail = ATOMIC_INIT(0);
+
+DEFINE_MUTEX(lrng_crypto_cb_update);
+
+/* DRNG for /dev/urandom, getrandom(2), get_random_bytes */
+static struct lrng_drng lrng_drng_init = {
+	.drng		= &chacha20,
+	.crypto_cb	= &lrng_cc20_crypto_cb,
+	.lock		= __MUTEX_INITIALIZER(lrng_drng_init.lock),
+	.spin_lock	= __SPIN_LOCK_UNLOCKED(lrng_drng_init.spin_lock)
+};
+
+/*
+ * DRNG for get_random_bytes when called in atomic context. This
+ * DRNG will always use the ChaCha20 DRNG. It will never benefit from a
+ * DRNG switch like the "regular" DRNG. If there was no DRNG switch, the atomic
+ * DRNG is identical to the "regular" DRNG.
+ *
+ * The reason for having this is due to the fact that DRNGs other than
+ * the ChaCha20 DRNG may sleep.
+ */
+static struct lrng_drng lrng_drng_atomic = {
+	.drng		= &chacha20,
+	.crypto_cb	= &lrng_cc20_crypto_cb,
+	.spin_lock	= __SPIN_LOCK_UNLOCKED(lrng_drng_atomic.spin_lock)
+};
+
+/********************************** Helper ************************************/
+
+bool lrng_get_available(void)
+{
+	return likely(atomic_read(&lrng_avail));
+}
+
+void lrng_set_available(void)
+{
+	atomic_set(&lrng_avail, 1);
+}
+
+struct lrng_drng *lrng_drng_init_instance(void)
+{
+	return &lrng_drng_init;
+}
+
+struct lrng_drng *lrng_drng_atomic_instance(void)
+{
+	return &lrng_drng_atomic;
+}
+
+void lrng_drng_reset(struct lrng_drng *drng)
+{
+	atomic_set(&drng->requests, LRNG_DRNG_RESEED_THRESH);
+	drng->last_seeded = jiffies;
+	drng->fully_seeded = false;
+	drng->force_reseed = true;
+	pr_debug("reset DRNG\n");
+}
+
+/* Initialize the default DRNG during boot */
+static void lrng_drngs_init_cc20(void)
+{
+	unsigned long flags = 0;
+
+	if (lrng_get_available())
+		return;
+
+	lrng_drng_lock(&lrng_drng_init, &flags);
+	if (lrng_get_available()) {
+		lrng_drng_unlock(&lrng_drng_init, &flags);
+		return;
+	}
+
+	lrng_drng_reset(&lrng_drng_init);
+	lrng_cc20_init_state(&chacha20);
+	lrng_state_init_seed_work();
+	lrng_drng_unlock(&lrng_drng_init, &flags);
+
+	lrng_drng_lock(&lrng_drng_atomic, &flags);
+	lrng_drng_reset(&lrng_drng_atomic);
+	/*
+	 * We do not initialize the state of the atomic DRNG as it is identical
+	 * to the DRNG at this point.
+	 */
+	lrng_drng_unlock(&lrng_drng_atomic, &flags);
+
+	lrng_set_available();
+}
+
+/************************* Random Number Generation ***************************/
+
+/* Inject a data buffer into the DRNG */
+static void lrng_drng_inject(struct lrng_drng *drng,
+			     const u8 *inbuf, u32 inbuflen)
+{
+	const char *drng_type = unlikely(drng == &lrng_drng_atomic) ?
+				"atomic" : "regular";
+	unsigned long flags = 0;
+
+	BUILD_BUG_ON(LRNG_DRNG_RESEED_THRESH > INT_MAX);
+	pr_debug("seeding %s DRNG with %u bytes\n", drng_type, inbuflen);
+	lrng_drng_lock(drng, &flags);
+	if (drng->crypto_cb->lrng_drng_seed_helper(drng->drng,
+						    inbuf, inbuflen) < 0) {
+		pr_warn("seeding of %s DRNG failed\n", drng_type);
+		atomic_set(&drng->requests, 1);
+	} else {
+		pr_debug("%s DRNG stats since last seeding: %lu secs; generate calls: %d\n",
+			 drng_type,
+			 (time_after(jiffies, drng->last_seeded) ?
+			  (jiffies - drng->last_seeded) : 0) / HZ,
+			 (LRNG_DRNG_RESEED_THRESH -
+			  atomic_read(&drng->requests)));
+		drng->last_seeded = jiffies;
+		atomic_set(&drng->requests, LRNG_DRNG_RESEED_THRESH);
+		drng->force_reseed = false;
+
+		if (drng->drng == lrng_drng_atomic.drng) {
+			lrng_drng_atomic.last_seeded = jiffies;
+			atomic_set(&lrng_drng_atomic.requests,
+				   LRNG_DRNG_RESEED_THRESH);
+			lrng_drng_atomic.force_reseed = false;
+		}
+	}
+	lrng_drng_unlock(drng, &flags);
+}
+
+/*
+ * Perform the seeding of the DRNG with data from noise source
+ */
+static inline int _lrng_drng_seed(struct lrng_drng *drng)
+{
+	struct entropy_buf seedbuf __aligned(LRNG_KCAPI_ALIGN);
+	unsigned long flags = 0;
+	u32 total_entropy_bits;
+	int ret;
+
+	lrng_drng_lock(drng, &flags);
+	total_entropy_bits = lrng_fill_seed_buffer(drng->crypto_cb, drng->hash,
+						   &seedbuf, 0);
+	lrng_drng_unlock(drng, &flags);
+
+	/* Allow the seeding operation to be called again */
+	lrng_pool_unlock();
+	lrng_init_ops(total_entropy_bits);
+	ret = total_entropy_bits >> 3;
+
+	lrng_drng_inject(drng, (u8 *)&seedbuf, sizeof(seedbuf));
+	memzero_explicit(&seedbuf, sizeof(seedbuf));
+
+	return ret;
+}
+
+static int lrng_drng_get(struct lrng_drng *drng, u8 *outbuf, u32 outbuflen);
+static void lrng_drng_seed(struct lrng_drng *drng)
+{
+	int ret = _lrng_drng_seed(drng);
+
+	if (ret >= LRNG_DRNG_SECURITY_STRENGTH_BYTES)
+		drng->fully_seeded = true;
+
+	BUILD_BUG_ON(LRNG_MIN_SEED_ENTROPY_BITS >
+		     LRNG_DRNG_SECURITY_STRENGTH_BITS);
+
+	/*
+	 * Reseed atomic DRNG from current DRNG,
+	 *
+	 * We can obtain random numbers from DRNG as the lock type
+	 * chosen by lrng_drng_get is usable with the current caller.
+	 */
+	if ((drng->drng != lrng_drng_atomic.drng) &&
+	    (lrng_drng_atomic.force_reseed ||
+	     atomic_read(&lrng_drng_atomic.requests) <= 0 ||
+	     time_after(jiffies, lrng_drng_atomic.last_seeded +
+			lrng_drng_reseed_max_time * HZ))) {
+		u8 seedbuf[LRNG_DRNG_SECURITY_STRENGTH_BYTES]
+						__aligned(LRNG_KCAPI_ALIGN);
+
+		ret = lrng_drng_get(drng, seedbuf, sizeof(seedbuf));
+
+		if (ret < 0) {
+			pr_warn("Error generating random numbers for atomic DRNG: %d\n",
+				ret);
+		} else {
+			lrng_drng_inject(&lrng_drng_atomic, seedbuf, ret);
+		}
+		memzero_explicit(&seedbuf, sizeof(seedbuf));
+	}
+}
+
+static inline void _lrng_drng_seed_work(struct lrng_drng *drng, u32 node)
+{
+	pr_debug("reseed triggered by interrupt noise source for DRNG on NUMA node %d\n",
+		 node);
+	lrng_drng_seed(drng);
+	if (drng->fully_seeded) {
+		/* Prevent reseed storm */
+		drng->last_seeded += node * 100 * HZ;
+		/* Prevent draining of pool on idle systems */
+		lrng_drng_reseed_max_time += 100;
+	}
+}
+
+/*
+ * DRNG reseed trigger: Kernel thread handler triggered by the schedule_work()
+ */
+void lrng_drng_seed_work(struct work_struct *dummy)
+{
+	struct lrng_drng **lrng_drng = lrng_drng_instances();
+	u32 node;
+
+	if (lrng_drng) {
+		for_each_online_node(node) {
+			struct lrng_drng *drng = lrng_drng[node];
+
+			if (drng && !drng->fully_seeded) {
+				_lrng_drng_seed_work(drng, node);
+				goto out;
+			}
+		}
+		lrng_pool_all_numa_nodes_seeded();
+	} else {
+		if (!lrng_drng_init.fully_seeded)
+			_lrng_drng_seed_work(&lrng_drng_init, 0);
+	}
+
+out:
+	/* Allow the seeding operation to be called again */
+	lrng_pool_unlock();
+}
+
+/* Force all DRNGs to reseed before next generation */
+void lrng_drng_force_reseed(void)
+{
+	struct lrng_drng **lrng_drng = lrng_drng_instances();
+	u32 node;
+
+	if (!lrng_drng) {
+		lrng_drng_init.force_reseed = true;
+		pr_debug("force reseed of initial DRNG\n");
+		return;
+	}
+	for_each_online_node(node) {
+		struct lrng_drng *drng = lrng_drng[node];
+
+		if (!drng)
+			continue;
+
+		drng->force_reseed = true;
+		pr_debug("force reseed of DRNG on node %u\n", node);
+	}
+	lrng_drng_atomic.force_reseed = true;
+}
+
+/**
+ * lrng_drng_get() - Get random data out of the DRNG which is reseeded
+ * frequently.
+ *
+ * @outbuf: buffer for storing random data
+ * @outbuflen: length of outbuf
+ *
+ * Return:
+ * * < 0 in error case (DRNG generation or update failed)
+ * * >=0 returning the returned number of bytes
+ */
+static int lrng_drng_get(struct lrng_drng *drng, u8 *outbuf, u32 outbuflen)
+{
+	unsigned long flags = 0;
+	u32 processed = 0;
+
+	if (!outbuf || !outbuflen)
+		return 0;
+
+	outbuflen = min_t(size_t, outbuflen, INT_MAX);
+
+	lrng_drngs_init_cc20();
+
+	while (outbuflen) {
+		u32 todo = min_t(u32, outbuflen, LRNG_DRNG_MAX_REQSIZE);
+		int ret;
+
+		/* All but the atomic DRNG are seeded during generation */
+		if (atomic_dec_and_test(&drng->requests) ||
+		    drng->force_reseed ||
+		    time_after(jiffies, drng->last_seeded +
+			       lrng_drng_reseed_max_time * HZ)) {
+			if (likely(drng != &lrng_drng_atomic)) {
+				if (lrng_pool_trylock())
+					atomic_set(&drng->requests, 1);
+				else
+					lrng_drng_seed(drng);
+			}
+		}
+
+		lrng_drng_lock(drng, &flags);
+		ret = drng->crypto_cb->lrng_drng_generate_helper(
+					drng->drng, outbuf + processed, todo);
+		lrng_drng_unlock(drng, &flags);
+		if (ret <= 0) {
+			pr_warn("getting random data from DRNG failed (%d)\n",
+				ret);
+			return -EFAULT;
+		}
+		processed += ret;
+		outbuflen -= ret;
+	}
+
+	return processed;
+}
+
+int lrng_drng_get_atomic(u8 *outbuf, u32 outbuflen)
+{
+	return lrng_drng_get(&lrng_drng_atomic, outbuf, outbuflen);
+}
+
+int lrng_drng_get_sleep(u8 *outbuf, u32 outbuflen)
+{
+	struct lrng_drng **lrng_drng = lrng_drng_instances();
+	struct lrng_drng *drng = &lrng_drng_init;
+	int node = numa_node_id();
+
+	might_sleep();
+
+	if (lrng_drng && lrng_drng[node] && lrng_drng[node]->fully_seeded)
+		drng = lrng_drng[node];
+
+	return lrng_drng_get(drng, outbuf, outbuflen);
+}
+
+/* Reset LRNG such that all existing entropy is gone */
+static void _lrng_reset(struct work_struct *work)
+{
+	struct lrng_drng **lrng_drng = lrng_drng_instances();
+	unsigned long flags = 0;
+
+	if (!lrng_drng) {
+		lrng_drng_lock(&lrng_drng_init, &flags);
+		lrng_drng_reset(&lrng_drng_init);
+		lrng_drng_unlock(&lrng_drng_init, &flags);
+	} else {
+		u32 node;
+
+		for_each_online_node(node) {
+			struct lrng_drng *drng = lrng_drng[node];
+
+			if (!drng)
+				continue;
+			lrng_drng_lock(drng, &flags);
+			lrng_drng_reset(drng);
+			lrng_drng_unlock(drng, &flags);
+		}
+	}
+	lrng_set_entropy_thresh(LRNG_INIT_ENTROPY_BITS +
+				LRNG_CONDITIONING_ENTROPY_LOSS);
+
+	lrng_reset_state();
+}
+
+static DECLARE_WORK(lrng_reset_work, _lrng_reset);
+
+void lrng_reset(void)
+{
+	schedule_work(&lrng_reset_work);
+}
+
+/***************************** Initialize LRNG *******************************/
+
+void __init lrng_drng_init_early(void)
+{
+	unsigned long flags = 0;
+
+	lrng_drng_lock(&lrng_drng_init, &flags);
+	lrng_cc20_init_state_boot(&chacha20);
+	lrng_drng_unlock(&lrng_drng_init, &flags);
+}
+
+static int __init lrng_init(void)
+{
+	lrng_drngs_init_cc20();
+
+	lrng_drngs_numa_alloc();
+	return 0;
+}
+
+late_initcall(lrng_init);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Stephan Mueller <smueller@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Linux Random Number Generator");
diff --git a/drivers/char/lrng/lrng_interfaces.c b/drivers/char/lrng/lrng_interfaces.c
new file mode 100644
index 000000000000..7fc04e54d834
--- /dev/null
+++ b/drivers/char/lrng/lrng_interfaces.c
@@ -0,0 +1,648 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG User and kernel space interfaces
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/freezer.h>
+#include <linux/fs.h>
+#include <linux/genhd.h>
+#include <linux/kthread.h>
+#include <linux/poll.h>
+#include <linux/preempt.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/timex.h>
+
+#include "lrng_internal.h"
+
+/*
+ * If the entropy count falls under this number of bits, then we
+ * should wake up processes which are selecting or polling on write
+ * access to /dev/random.
+ */
+u32 lrng_write_wakeup_bits = LRNG_WRITE_WAKEUP_ENTROPY;
+
+static LIST_HEAD(lrng_ready_list);
+static DEFINE_SPINLOCK(lrng_ready_list_lock);
+
+static DECLARE_WAIT_QUEUE_HEAD(lrng_write_wait);
+static DECLARE_WAIT_QUEUE_HEAD(lrng_init_wait);
+static struct fasync_struct *fasync;
+
+struct ctl_table random_table[];
+/********************************** Helper ***********************************/
+
+/* Is the DRNG seed level too low? */
+static inline bool lrng_need_entropy(void)
+{
+	return (lrng_avail_entropy() < lrng_write_wakeup_bits);
+}
+
+void lrng_writer_wakeup(void)
+{
+	if (lrng_need_entropy() && wq_has_sleeper(&lrng_write_wait)) {
+		wake_up_interruptible(&lrng_write_wait);
+		kill_fasync(&fasync, SIGIO, POLL_OUT);
+	}
+}
+
+void lrng_init_wakeup(void)
+{
+	wake_up_all(&lrng_init_wait);
+	kill_fasync(&fasync, SIGIO, POLL_IN);
+}
+
+/**
+ * lrng_process_ready_list() - Ping all kernel internal callers waiting until
+ * the DRNG is at least minimally seeded to inform that the DRNG reached that
+ * seed level.
+ *
+ * When the SP800-90B testing is enabled, the ping only happens if the SP800-90B
+ * startup health tests are completed. This implies that kernel internal
+ * callers always have an SP800-90B compliant noise source when being
+ * pinged.
+ */
+void lrng_process_ready_list(void)
+{
+	unsigned long flags;
+	struct random_ready_callback *rdy, *tmp;
+
+	if (!lrng_sp80090b_startup_complete())
+		return;
+
+	spin_lock_irqsave(&lrng_ready_list_lock, flags);
+	list_for_each_entry_safe(rdy, tmp, &lrng_ready_list, list) {
+		struct module *owner = rdy->owner;
+
+		list_del_init(&rdy->list);
+		rdy->func(rdy);
+		module_put(owner);
+	}
+	spin_unlock_irqrestore(&lrng_ready_list_lock, flags);
+}
+
+void lrng_debug_report_seedlevel(const char *name)
+{
+#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
+	static void *previous = NULL;
+	void *caller = (void *) _RET_IP_;
+
+	if (READ_ONCE(previous) == caller)
+		return;
+
+	if (!lrng_state_min_seeded())
+		pr_notice("%pS %s called without reaching mimimally seeded level (available entropy %u)\n",
+			  caller, name, lrng_avail_entropy());
+
+	WRITE_ONCE(previous, caller);
+#endif
+}
+
+/************************ LRNG kernel input interfaces ************************/
+
+/**
+ * add_hwgenerator_randomness() - Interface for in-kernel drivers of true
+ * hardware RNGs.
+ *
+ * Those devices may produce endless random bits and will be throttled
+ * when our pool is full.
+ *
+ * @buffer: buffer holding the entropic data from HW noise sources to be used to
+ *	    insert into entropy pool.
+ * @count: length of buffer
+ * @entropy_bits: amount of entropy in buffer (value is in bits)
+ */
+void add_hwgenerator_randomness(const char *buffer, size_t count,
+				size_t entropy_bits)
+{
+	/*
+	 * Suspend writing if we are fully loaded with entropy.
+	 * We'll be woken up again once below lrng_write_wakeup_thresh,
+	 * or when the calling thread is about to terminate.
+	 */
+	wait_event_interruptible(lrng_write_wait,
+				lrng_need_entropy() ||
+				lrng_state_exseed_allow(lrng_noise_source_hw) ||
+				kthread_should_stop());
+	lrng_state_exseed_set(lrng_noise_source_hw, false);
+	lrng_pool_lfsr_nonaligned(buffer, count);
+	lrng_pool_add_entropy(entropy_bits);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
+
+/**
+ * add_bootloader_randomness() - Handle random seed passed by bootloader.
+ *
+ * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
+ * it would be regarded as device data.
+ * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
+ *
+ * @buf: buffer holding the entropic data from HW noise sources to be used to
+ *	 insert into entropy pool.
+ * @size: length of buffer
+ */
+void add_bootloader_randomness(const void *buf, unsigned int size)
+{
+	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
+		add_hwgenerator_randomness(buf, size, size * 8);
+	else
+		add_device_randomness(buf, size);
+}
+EXPORT_SYMBOL_GPL(add_bootloader_randomness);
+
+/*
+ * Callback for HID layer -- use the HID event values to stir the entropy pool
+ */
+void add_input_randomness(unsigned int type, unsigned int code,
+			  unsigned int value)
+{
+	static unsigned char last_value;
+
+	/* ignore autorepeat and the like */
+	if (value == last_value)
+		return;
+
+	last_value = value;
+
+	lrng_pool_lfsr_u32((type << 4) ^ code ^ (code >> 4) ^ value);
+}
+EXPORT_SYMBOL_GPL(add_input_randomness);
+
+/**
+ * add_device_randomness() - Add device- or boot-specific data to the entropy
+ * pool to help initialize it.
+ *
+ * None of this adds any entropy; it is meant to avoid the problem of
+ * the entropy pool having similar initial state across largely
+ * identical devices.
+ *
+ * @buf: buffer holding the entropic data from HW noise sources to be used to
+ *	 insert into entropy pool.
+ * @size: length of buffer
+ */
+void add_device_randomness(const void *buf, unsigned int size)
+{
+	lrng_pool_lfsr_nonaligned((u8 *)buf, size);
+	lrng_pool_lfsr_u32(random_get_entropy());
+	lrng_pool_lfsr_u32(jiffies);
+}
+EXPORT_SYMBOL(add_device_randomness);
+
+#ifdef CONFIG_BLOCK
+void rand_initialize_disk(struct gendisk *disk) { }
+void add_disk_randomness(struct gendisk *disk) { }
+EXPORT_SYMBOL(add_disk_randomness);
+#endif
+
+/**
+ * del_random_ready_callback() - Delete a previously registered readiness
+ * callback function.
+ *
+ * @rdy: callback definition that was registered initially
+ */
+void del_random_ready_callback(struct random_ready_callback *rdy)
+{
+	unsigned long flags;
+	struct module *owner = NULL;
+
+	spin_lock_irqsave(&lrng_ready_list_lock, flags);
+	if (!list_empty(&rdy->list)) {
+		list_del_init(&rdy->list);
+		owner = rdy->owner;
+	}
+	spin_unlock_irqrestore(&lrng_ready_list_lock, flags);
+
+	module_put(owner);
+}
+EXPORT_SYMBOL(del_random_ready_callback);
+
+/**
+ * add_random_ready_callback() - Add a callback function that will be invoked
+ * when the DRNG is mimimally seeded.
+ *
+ * @rdy: callback definition to be invoked when the LRNG is seeded
+ *
+ * Return:
+ * * 0 if callback is successfully added
+ * * -EALREADY if pool is already initialised (callback not called)
+ * * -ENOENT if module for callback is not alive
+ */
+int add_random_ready_callback(struct random_ready_callback *rdy)
+{
+	struct module *owner;
+	unsigned long flags;
+	int err = -EALREADY;
+
+	if (likely(lrng_state_min_seeded()))
+		return err;
+
+	owner = rdy->owner;
+	if (!try_module_get(owner))
+		return -ENOENT;
+
+	spin_lock_irqsave(&lrng_ready_list_lock, flags);
+	if (lrng_state_min_seeded())
+		goto out;
+
+	owner = NULL;
+
+	list_add(&rdy->list, &lrng_ready_list);
+	err = 0;
+
+out:
+	spin_unlock_irqrestore(&lrng_ready_list_lock, flags);
+
+	module_put(owner);
+
+	return err;
+}
+EXPORT_SYMBOL(add_random_ready_callback);
+
+/*********************** LRNG kernel output interfaces ************************/
+
+/**
+ * get_random_bytes() - Provider of cryptographic strong random numbers for
+ * kernel-internal usage.
+ *
+ * This function is appropriate for all in-kernel use cases. However,
+ * it will always use the ChaCha20 DRNG.
+ *
+ * @buf: buffer to store the random bytes
+ * @nbytes: size of the buffer
+ */
+void get_random_bytes(void *buf, int nbytes)
+{
+	lrng_drng_get_atomic((u8 *)buf, (u32)nbytes);
+	lrng_debug_report_seedlevel("get_random_bytes");
+}
+EXPORT_SYMBOL(get_random_bytes);
+
+/**
+ * get_random_bytes_full() - Provider of cryptographic strong random numbers
+ * for kernel-internal usage.
+ *
+ * This function is appropriate only for non-atomic use cases as this
+ * function may sleep. Though, it provides access to the full functionality
+ * of LRNG including the switchable DRNG support, that may support other
+ * DRNGs such as the SP800-90A DRBG.
+ *
+ * @buf: buffer to store the random bytes
+ * @nbytes: size of the buffer
+ */
+void get_random_bytes_full(void *buf, int nbytes)
+{
+	lrng_drng_get_sleep((u8 *)buf, (u32)nbytes);
+	lrng_debug_report_seedlevel("get_random_bytes_full");
+}
+EXPORT_SYMBOL(get_random_bytes_full);
+
+/**
+ * wait_for_random_bytes() - Wait for the LRNG to be seeded and thus
+ * guaranteed to supply cryptographically secure random numbers.
+ *
+ * This applies to: the /dev/urandom device, the get_random_bytes function,
+ * and the get_random_{u32,u64,int,long} family of functions. Using any of
+ * these functions without first calling this function forfeits the guarantee
+ * of security.
+ *
+ * Return:
+ * * 0 if the LRNG has been seeded.
+ * * -ERESTARTSYS if the function was interrupted by a signal.
+ */
+int wait_for_random_bytes(void)
+{
+	if (likely(lrng_state_min_seeded()))
+		return 0;
+	return wait_event_interruptible(lrng_init_wait,
+					lrng_state_min_seeded());
+}
+EXPORT_SYMBOL(wait_for_random_bytes);
+
+/**
+ * get_random_bytes_arch() - This function will use the architecture-specific
+ * hardware random number generator if it is available.
+ *
+ * The arch-specific hw RNG will almost certainly be faster than what we can
+ * do in software, but it is impossible to verify that it is implemented
+ * securely (as opposed, to, say, the AES encryption of a sequence number using
+ * a key known by the NSA).  So it's useful if we need the speed, but only if
+ * we're willing to trust the hardware manufacturer not to have put in a back
+ * door.
+ *
+ * @buf: buffer allocated by caller to store the random data in
+ * @nbytes: length of outbuf
+ *
+ * Return: number of bytes filled in.
+ */
+int __must_check get_random_bytes_arch(void *buf, int nbytes)
+{
+	u8 *p = buf;
+
+	while (nbytes) {
+		unsigned long v;
+		int chunk = min_t(int, nbytes, sizeof(unsigned long));
+
+		if (!arch_get_random_long(&v))
+			break;
+
+		memcpy(p, &v, chunk);
+		p += chunk;
+		nbytes -= chunk;
+	}
+
+	if (nbytes)
+		lrng_drng_get_atomic((u8 *)p, (u32)nbytes);
+
+	return nbytes;
+}
+EXPORT_SYMBOL(get_random_bytes_arch);
+
+/*
+ * Returns whether or not the LRNG has been seeded.
+ *
+ * Returns: true if the urandom pool has been seeded.
+ *          false if the urandom pool has not been seeded.
+ */
+bool rng_is_initialized(void)
+{
+	return lrng_state_operational();
+}
+EXPORT_SYMBOL(rng_is_initialized);
+
+/************************ LRNG user output interfaces *************************/
+
+static ssize_t lrng_read_common(char __user *buf, size_t nbytes)
+{
+	ssize_t ret = 0;
+	u8 tmpbuf[LRNG_DRNG_BLOCKSIZE] __aligned(LRNG_KCAPI_ALIGN);
+	u8 *tmp_large = NULL, *tmp = tmpbuf;
+	u32 tmplen = sizeof(tmpbuf);
+
+	if (nbytes == 0)
+		return 0;
+
+	/*
+	 * Satisfy large read requests -- as the common case are smaller
+	 * request sizes, such as 16 or 32 bytes, avoid a kmalloc overhead for
+	 * those by using the stack variable of tmpbuf.
+	 */
+	if (!CONFIG_BASE_SMALL && (nbytes > sizeof(tmpbuf))) {
+		tmplen = min_t(u32, nbytes, LRNG_DRNG_MAX_REQSIZE);
+		tmp_large = kmalloc(tmplen + LRNG_KCAPI_ALIGN, GFP_KERNEL);
+		if (!tmp_large)
+			tmplen = sizeof(tmpbuf);
+		else
+			tmp = PTR_ALIGN(tmp_large, LRNG_KCAPI_ALIGN);
+	}
+
+	while (nbytes) {
+		u32 todo = min_t(u32, nbytes, tmplen);
+		int rc = 0;
+
+		/* Reschedule if we received a large request. */
+		if ((tmp_large) && need_resched()) {
+			if (signal_pending(current)) {
+				if (ret == 0)
+					ret = -ERESTARTSYS;
+				break;
+			}
+			schedule();
+		}
+
+		rc = lrng_drng_get_sleep(tmp, todo);
+		if (rc <= 0) {
+			if (rc < 0)
+				ret = rc;
+			break;
+		}
+		if (copy_to_user(buf, tmp, rc)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		nbytes -= rc;
+		buf += rc;
+		ret += rc;
+	}
+
+	/* Wipe data just returned from memory */
+	if (tmp_large)
+		kzfree(tmp_large);
+	else
+		memzero_explicit(tmpbuf, sizeof(tmpbuf));
+
+	return ret;
+}
+
+static ssize_t
+lrng_read_common_block(int nonblock, char __user *buf, size_t nbytes)
+{
+	if (nbytes == 0)
+		return 0;
+
+	if (unlikely(!lrng_state_operational())) {
+		int ret;
+
+		if (nonblock)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(lrng_init_wait,
+					       lrng_state_operational());
+		if (unlikely(ret))
+			return ret;
+	}
+
+	return lrng_read_common(buf, nbytes);
+}
+
+static ssize_t lrng_drng_read_block(struct file *file, char __user *buf,
+				     size_t nbytes, loff_t *ppos)
+{
+	return lrng_read_common_block(file->f_flags & O_NONBLOCK, buf, nbytes);
+}
+
+static unsigned int lrng_random_poll(struct file *file, poll_table *wait)
+{
+	__poll_t mask;
+
+	poll_wait(file, &lrng_init_wait, wait);
+	poll_wait(file, &lrng_write_wait, wait);
+	mask = 0;
+	if (lrng_state_operational())
+		mask |= EPOLLIN | EPOLLRDNORM;
+	if (lrng_need_entropy() ||
+	    lrng_state_exseed_allow(lrng_noise_source_user))
+		mask |= EPOLLOUT | EPOLLWRNORM;
+	return mask;
+}
+
+static ssize_t lrng_drng_write_common(const char __user *buffer, size_t count,
+				      u32 entropy_bits)
+{
+	ssize_t ret = 0;
+	u8 buf[64] __aligned(LRNG_KCAPI_ALIGN);
+	const char __user *p = buffer;
+	u32 orig_entropy_bits = entropy_bits;
+
+	if (!lrng_get_available())
+		return -EAGAIN;
+
+	count = min_t(size_t, count, INT_MAX);
+	while (count > 0) {
+		size_t bytes = min_t(size_t, count, sizeof(buf));
+		u32 ent = min_t(u32, bytes<<3, entropy_bits);
+
+		if (copy_from_user(&buf, p, bytes))
+			return -EFAULT;
+		/* Inject data into entropy pool */
+		lrng_pool_lfsr(buf, bytes);
+		lrng_pool_add_entropy(ent);
+
+		count -= bytes;
+		p += bytes;
+		ret += bytes;
+		entropy_bits -= ent;
+
+		cond_resched();
+	}
+
+	/* Force reseed of DRNG during next data request. */
+	if (!orig_entropy_bits)
+		lrng_drng_force_reseed();
+
+	return ret;
+}
+
+static ssize_t lrng_drng_read(struct file *file, char __user *buf,
+			      size_t nbytes, loff_t *ppos)
+{
+	if (!lrng_state_min_seeded())
+		pr_notice_ratelimited("%s - use of insufficiently seeded DRNG (%zu bytes read)\n",
+				      current->comm, nbytes);
+	else if (!lrng_state_operational())
+		pr_debug_ratelimited("%s - use of not fully seeded DRNG (%zu bytes read)\n",
+				     current->comm, nbytes);
+
+	return lrng_read_common(buf, nbytes);
+}
+
+static ssize_t lrng_drng_write(struct file *file, const char __user *buffer,
+			       size_t count, loff_t *ppos)
+{
+	return lrng_drng_write_common(buffer, count, 0);
+}
+
+static long lrng_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
+{
+	int size, ent_count_bits;
+	int __user *p = (int __user *)arg;
+
+	switch (cmd) {
+	case RNDGETENTCNT:
+		ent_count_bits = lrng_avail_entropy();
+		if (put_user(ent_count_bits, p))
+			return -EFAULT;
+		return 0;
+	case RNDADDTOENTCNT:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		if (get_user(ent_count_bits, p))
+			return -EFAULT;
+		ent_count_bits = (int)lrng_avail_entropy() + ent_count_bits;
+		if (ent_count_bits < 0)
+			ent_count_bits = 0;
+		if (ent_count_bits > LRNG_POOL_SIZE_BITS)
+			ent_count_bits = LRNG_POOL_SIZE_BITS;
+		lrng_pool_set_entropy(ent_count_bits);
+		return 0;
+	case RNDADDENTROPY:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		if (get_user(ent_count_bits, p++))
+			return -EFAULT;
+		if (ent_count_bits < 0)
+			return -EINVAL;
+		if (get_user(size, p++))
+			return -EFAULT;
+		if (size < 0)
+			return -EINVAL;
+		lrng_state_exseed_set(lrng_noise_source_user, false);
+		/* there cannot be more entropy than data */
+		ent_count_bits = min(ent_count_bits, size<<3);
+		return lrng_drng_write_common((const char __user *)p, size,
+					      ent_count_bits);
+	case RNDZAPENTCNT:
+	case RNDCLEARPOOL:
+		/* Clear the entropy pool counter. */
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		lrng_pool_set_entropy(0);
+		return 0;
+	case RNDRESEEDCRNG:
+		/*
+		 * We leave the capability check here since it is present
+		 * in the upstream's RNG implementation. Yet, user space
+		 * can trigger a reseed as easy as writing into /dev/random
+		 * or /dev/urandom where no privilege is needed.
+		 */
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		/* Force a reseed of all DRNGs */
+		lrng_drng_force_reseed();
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int lrng_fasync(int fd, struct file *filp, int on)
+{
+	return fasync_helper(fd, filp, on, &fasync);
+}
+
+const struct file_operations random_fops = {
+	.read  = lrng_drng_read_block,
+	.write = lrng_drng_write,
+	.poll  = lrng_random_poll,
+	.unlocked_ioctl = lrng_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+	.fasync = lrng_fasync,
+	.llseek = noop_llseek,
+};
+
+const struct file_operations urandom_fops = {
+	.read  = lrng_drng_read,
+	.write = lrng_drng_write,
+	.unlocked_ioctl = lrng_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+	.fasync = lrng_fasync,
+	.llseek = noop_llseek,
+};
+
+SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
+		unsigned int, flags)
+{
+	if (flags & ~(GRND_NONBLOCK|GRND_RANDOM|GRND_INSECURE))
+		return -EINVAL;
+
+	/*
+	 * Requesting insecure and blocking randomness at the same time makes
+	 * no sense.
+	 */
+	if ((flags &
+	     (GRND_INSECURE|GRND_RANDOM)) == (GRND_INSECURE|GRND_RANDOM))
+		return -EINVAL;
+
+	if (count > INT_MAX)
+		count = INT_MAX;
+
+	if (flags & GRND_INSECURE)
+		return lrng_drng_read(NULL, buf, count, NULL);
+
+	return lrng_read_common_block(flags & GRND_NONBLOCK, buf, count);
+}
diff --git a/drivers/char/lrng/lrng_internal.h b/drivers/char/lrng/lrng_internal.h
new file mode 100644
index 000000000000..f6a5f0d960c1
--- /dev/null
+++ b/drivers/char/lrng/lrng_internal.h
@@ -0,0 +1,333 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * Copyright (C) 2018 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#ifndef _LRNG_INTERNAL_H
+#define _LRNG_INTERNAL_H
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+
+/*************************** General LRNG parameter ***************************/
+
+/* Entropy pool parameter
+ *
+ * The LRNG_POOL_SIZE cannot be smaller than 64 bytes as the SHA-1 operation
+ * in lrng_chacha20.c requires multiples of 64 bytes
+ */
+#define LRNG_POOL_SIZE			(16 << CONFIG_LRNG_POOL_SIZE)
+#define LRNG_POOL_WORD_BYTES		(4)	/* (sizeof(atomic_t)) */
+#define LRNG_POOL_SIZE_BYTES		(LRNG_POOL_SIZE * LRNG_POOL_WORD_BYTES)
+#define LRNG_POOL_SIZE_BITS		(LRNG_POOL_SIZE_BYTES * 8)
+#define LRNG_POOL_WORD_BITS		(LRNG_POOL_WORD_BYTES * 8)
+
+/* Security strength of LRNG -- this must match DRNG security strength */
+#define LRNG_DRNG_SECURITY_STRENGTH_BYTES 32
+#define LRNG_DRNG_SECURITY_STRENGTH_BITS (LRNG_DRNG_SECURITY_STRENGTH_BYTES * 8)
+#define LRNG_DRNG_BLOCKSIZE 64		/* Maximum of DRNG block sizes */
+
+/*
+ * SP800-90A defines a maximum request size of 1<<16 bytes. The given value is
+ * considered a safer margin.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_DRNG_MAX_REQSIZE		(1<<12)
+
+/*
+ * SP800-90A defines a maximum number of requests between reseeds of 2^48.
+ * The given value is considered a much safer margin, balancing requests for
+ * frequent reseeds with the need to conserve entropy. This value MUST NOT be
+ * larger than INT_MAX because it is used in an atomic_t.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_DRNG_RESEED_THRESH		(1<<20)
+
+/*
+ * Number of interrupts to be recorded to assume that DRNG security strength
+ * bits of entropy are received.
+ * Note: a value below the DRNG security strength should not be defined as this
+ *	 may imply the DRNG can never be fully seeded in case other noise
+ *	 sources are unavailable.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_IRQ_ENTROPY_BITS		LRNG_DRNG_SECURITY_STRENGTH_BITS
+
+/*
+ * Min required seed entropy is 128 bits covering the minimum entropy
+ * requirement of SP800-131A and the German BSI's TR02102.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_FULL_SEED_ENTROPY_BITS	LRNG_DRNG_SECURITY_STRENGTH_BITS
+#define LRNG_MIN_SEED_ENTROPY_BITS	128
+#define LRNG_INIT_ENTROPY_BITS		32
+
+/*
+ * Amount of entropy that is lost with the conditioning functions of LFSR and
+ * hash_df as shown with the entropy analysis compliant to SP800-90B.
+ */
+#define LRNG_CONDITIONING_ENTROPY_LOSS	1
+
+/*
+ * Wakeup value
+ *
+ * This value is allowed to be changed.
+ */
+#if (LRNG_POOL_SIZE_BITS <= (LRNG_DRNG_SECURITY_STRENGTH_BITS * 2))
+# define LRNG_WRITE_WAKEUP_ENTROPY	(LRNG_DRNG_SECURITY_STRENGTH_BITS + \
+					LRNG_CONDITIONING_ENTROPY_LOSS)
+#else
+# define LRNG_WRITE_WAKEUP_ENTROPY	(LRNG_DRNG_SECURITY_STRENGTH_BITS * 2)
+#endif
+
+/*
+ * Oversampling factor of IRQ events to obtain
+ * LRNG_DRNG_SECURITY_STRENGTH_BYTES. This factor is used when a
+ * high-resolution time stamp is not available. In this case, jiffies and
+ * register contents are used to fill the entropy pool. These noise sources
+ * are much less entropic than the high-resolution timer. The entropy content
+ * is the entropy content assumed with LRNG_IRQ_ENTROPY_BITS divided by
+ * LRNG_IRQ_OVERSAMPLING_FACTOR.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_IRQ_OVERSAMPLING_FACTOR	10
+
+/*
+ * Alignmask which should cover all cipher implementations
+ * WARNING: If this is changed to a value larger than 8, manual
+ * alignment is necessary as older versions of GCC may not be capable
+ * of aligning stack variables at boundaries greater than 8.
+ * In this case, PTR_ALIGN must be used.
+ */
+#define LRNG_KCAPI_ALIGN		8
+
+/************************ Default DRNG implementation *************************/
+
+extern struct chacha20_state chacha20;
+extern const struct lrng_crypto_cb lrng_cc20_crypto_cb;
+void lrng_cc20_init_state(struct chacha20_state *state);
+void lrng_cc20_init_state_boot(struct chacha20_state *state);
+
+/********************************** /proc *************************************/
+
+static inline void lrng_pool_inc_numa_node(void) { }
+
+/****************************** LRNG interfaces *******************************/
+
+extern u32 lrng_write_wakeup_bits;
+extern int lrng_drng_reseed_max_time;
+
+void lrng_writer_wakeup(void);
+void lrng_init_wakeup(void);
+void lrng_debug_report_seedlevel(const char *name);
+void lrng_process_ready_list(void);
+
+/************************** Entropy pool management ***************************/
+
+enum lrng_external_noise_source {
+	lrng_noise_source_hw,
+	lrng_noise_source_user
+};
+
+bool lrng_state_exseed_allow(enum lrng_external_noise_source source);
+void lrng_state_exseed_set(enum lrng_external_noise_source source, bool type);
+void lrng_state_init_seed_work(void);
+u32 lrng_avail_entropy(void);
+void lrng_set_entropy_thresh(u32 new);
+int lrng_pool_trylock(void);
+void lrng_pool_unlock(void);
+void lrng_reset_state(void);
+void lrng_pool_all_numa_nodes_seeded(void);
+bool lrng_state_min_seeded(void);
+bool lrng_state_fully_seeded(void);
+bool lrng_state_operational(void);
+bool lrng_pool_highres_timer(void);
+void lrng_pool_set_entropy(u32 entropy_bits);
+void lrng_pool_lfsr(const u8 *buf, u32 buflen);
+void lrng_pool_lfsr_nonaligned(const u8 *buf, u32 buflen);
+void lrng_pool_lfsr_u32(u32 value);
+void lrng_pool_add_irq(u32 irq_num);
+void lrng_pool_add_entropy(u32 entropy_bits);
+
+struct entropy_buf {
+	u8 a[LRNG_DRNG_SECURITY_STRENGTH_BYTES];
+	u8 b[LRNG_DRNG_SECURITY_STRENGTH_BYTES];
+	u8 c[LRNG_DRNG_SECURITY_STRENGTH_BYTES];
+	u32 now;
+};
+
+int lrng_fill_seed_buffer(const struct lrng_crypto_cb *crypto_cb, void *hash,
+			  struct entropy_buf *entropy_buf, u32 entropy_retain);
+void lrng_init_ops(u32 seed_bits);
+
+/************************** Jitter RNG Noise Source ***************************/
+
+#ifdef CONFIG_LRNG_JENT
+u32 lrng_get_jent(u8 *outbuf, unsigned int outbuflen);
+u32 lrng_jent_entropylevel(void);
+#else /* CONFIG_CRYPTO_JITTERENTROPY */
+static inline u32 lrng_get_jent(u8 *outbuf, unsigned int outbuflen) {return 0; }
+static inline u32 lrng_jent_entropylevel(void) { return 0; }
+#endif /* CONFIG_CRYPTO_JITTERENTROPY */
+
+/*************************** CPU-based Noise Source ***************************/
+
+u32 lrng_get_arch(u8 *outbuf);
+u32 lrng_slow_noise_req_entropy(u32 required_entropy_bits);
+
+/****************************** DRNG processing *******************************/
+
+/* Secondary DRNG state handle */
+struct lrng_drng {
+	void *drng;				/* DRNG handle */
+	void *hash;				/* Hash handle */
+	const struct lrng_crypto_cb *crypto_cb;	/* Crypto callbacks */
+	atomic_t requests;			/* Number of DRNG requests */
+	unsigned long last_seeded;		/* Last time it was seeded */
+	bool fully_seeded;			/* Is DRNG fully seeded? */
+	bool force_reseed;			/* Force a reseed */
+	struct mutex lock;
+	spinlock_t spin_lock;
+};
+
+extern struct mutex lrng_crypto_cb_update;
+
+struct lrng_drng *lrng_drng_init_instance(void);
+struct lrng_drng *lrng_drng_atomic_instance(void);
+
+static __always_inline bool lrng_drng_is_atomic(struct lrng_drng *drng)
+{
+	return (drng->drng == lrng_drng_atomic_instance()->drng);
+}
+
+/* Lock the DRNG */
+static __always_inline void lrng_drng_lock(struct lrng_drng *drng,
+					   unsigned long *flags)
+{
+	/* Use spin lock in case the atomic DRNG context is used */
+	if (lrng_drng_is_atomic(drng)) {
+		spin_lock_irqsave(&drng->spin_lock, *flags);
+
+		/*
+		 * In case a lock transition happened while we were spinning,
+		 * catch this case and use the new lock type.
+		 */
+		if (!lrng_drng_is_atomic(drng)) {
+			spin_unlock_irqrestore(&drng->spin_lock, *flags);
+			mutex_lock(&drng->lock);
+		}
+	} else {
+		mutex_lock(&drng->lock);
+	}
+}
+
+/* Unlock the DRNG */
+static __always_inline void lrng_drng_unlock(struct lrng_drng *drng,
+					     unsigned long *flags)
+{
+	if (lrng_drng_is_atomic(drng))
+		spin_unlock_irqrestore(&drng->spin_lock, *flags);
+	else
+		mutex_unlock(&drng->lock);
+}
+
+void lrng_drng_init_early(void);
+bool lrng_get_available(void);
+void lrng_set_available(void);
+void lrng_drng_reset(struct lrng_drng *drng);
+int lrng_drng_get_atomic(u8 *outbuf, u32 outbuflen);
+int lrng_drng_get_sleep(u8 *outbuf, u32 outbuflen);
+void lrng_drng_force_reseed(void);
+void lrng_drng_seed_work(struct work_struct *dummy);
+
+static inline struct lrng_drng **lrng_drng_instances(void) { return NULL; }
+static inline void lrng_drngs_numa_alloc(void) { return; }
+
+/************************** Health Test linking code **************************/
+
+enum lrng_health_res {
+	lrng_health_pass,		/* Health test passes on time stamp */
+	lrng_health_fail_use,		/* Time stamp unhealthy, but mix in */
+	lrng_health_fail_drop		/* Time stamp unhealthy, drop it */
+};
+
+#ifdef CONFIG_LRNG_HEALTH_TESTS
+bool lrng_sp80090b_startup_complete(void);
+bool lrng_sp80090b_compliant(void);
+
+enum lrng_health_res lrng_health_test(u32 now_time);
+void lrng_health_disable(void);
+
+void lrng_reset(void);
+#else	/* CONFIG_LRNG_HEALTH_TESTS */
+static inline bool lrng_sp80090b_startup_complete(void) { return true; }
+static inline bool lrng_sp80090b_compliant(void) { return false; }
+
+static inline enum lrng_health_res
+lrng_health_test(u32 now_time) { return lrng_health_pass; }
+static inline void lrng_health_disable(void) { }
+#endif	/* CONFIG_LRNG_HEALTH_TESTS */
+
+/****************************** Helper code ***********************************/
+
+static inline u32 atomic_read_u32(atomic_t *v)
+{
+	return (u32)atomic_read(v);
+}
+
+/*************************** Auxiliary functions ******************************/
+
+void invalidate_batched_entropy(void);
+
+/***************************** Testing code ***********************************/
+
+#ifdef CONFIG_LRNG_RAW_HIRES_ENTROPY
+bool lrng_raw_hires_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_HIRES_ENTROPY */
+static inline bool lrng_raw_hires_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_HIRES_ENTROPY */
+
+#ifdef CONFIG_LRNG_RAW_JIFFIES_ENTROPY
+bool lrng_raw_jiffies_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_JIFFIES_ENTROPY */
+static inline bool lrng_raw_jiffies_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_JIFFIES_ENTROPY */
+
+#ifdef CONFIG_LRNG_RAW_IRQ_ENTROPY
+bool lrng_raw_irq_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_IRQ_ENTROPY */
+static inline bool lrng_raw_irq_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_IRQ_ENTROPY */
+
+#ifdef CONFIG_LRNG_RAW_IRQFLAGS_ENTROPY
+bool lrng_raw_irqflags_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_IRQFLAGS_ENTROPY */
+static inline bool lrng_raw_irqflags_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_IRQFLAGS_ENTROPY */
+
+#ifdef CONFIG_LRNG_RAW_RETIP_ENTROPY
+bool lrng_raw_retip_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_RETIP_ENTROPY */
+static inline bool lrng_raw_retip_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_RETIP_ENTROPY */
+
+#ifdef CONFIG_LRNG_RAW_ARRAY
+bool lrng_raw_array_entropy_store(u32 value);
+#else	/* CONFIG_LRNG_RAW_ARRAY */
+static inline bool lrng_raw_array_entropy_store(u32 value) { return false; }
+#endif	/* CONFIG_LRNG_RAW_ARRAY */
+
+#ifdef CONFIG_LRNG_IRQ_PERF
+bool lrng_perf_time(u32 start);
+#else /* CONFIG_LRNG_IRQ_PERF */
+static inline bool lrng_perf_time(u32 start) { return false; }
+#endif /*CONFIG_LRNG_IRQ_PERF */
+
+#endif /* _LRNG_INTERNAL_H */
diff --git a/drivers/char/lrng/lrng_lfsr.h b/drivers/char/lrng/lrng_lfsr.h
new file mode 100644
index 000000000000..1b096a58fccc
--- /dev/null
+++ b/drivers/char/lrng/lrng_lfsr.h
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * LRNG Linear Feedback Shift Register
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+/* Status information about IRQ noise source */
+struct lrng_irq_info {
+	atomic_t num_events;	/* Number of healthy IRQs since last read */
+	atomic_t num_events_thresh;	/* Reseed threshold */
+	atomic_t reseed_in_progress;	/* Flag for on executing reseed */
+	bool irq_highres_timer;	/* Is high-resolution timer available? */
+	u32 irq_entropy_bits;	/* LRNG_IRQ_ENTROPY_BITS? */
+};
+
+/*
+ * This is the entropy pool used by the slow noise source. Its size should
+ * be at least as large as LRNG_DRNG_SECURITY_STRENGTH_BITS.
+ *
+ * The pool array is aligned to 8 bytes to comfort the kernel crypto API cipher
+ * implementations of the hash functions used to read the pool: for some
+ * accelerated implementations, we need an alignment to avoid a realignment
+ * which involves memcpy(). The alignment to 8 bytes should satisfy all crypto
+ * implementations.
+ *
+ * LRNG_POOL_SIZE is allowed to be changed only if the taps of the polynomial
+ * used for the LFSR are changed as well. The size must be in powers of 2 due
+ * to the mask handling in lrng_pool_lfsr_u32 which uses AND instead of modulo.
+ */
+struct lrng_pool {
+	union {
+		struct {
+			/*
+			 * hash_df implementation: counter, requested_bits and
+			 * pool form a linear buffer that is used in the
+			 * hash_df function specified in SP800-90A section
+			 * 10.3.1
+			 */
+			unsigned char counter;
+			__be32 requested_bits;
+
+			/* Pool */
+			atomic_t pool[LRNG_POOL_SIZE] __latent_entropy;
+			/* Ptr into pool for next IRQ word injection */
+			atomic_t pool_ptr;
+			/* rotate for LFSR */
+			atomic_t input_rotate;
+			/* All NUMA DRNGs seeded? */
+			bool all_online_numa_node_seeded;
+			/* IRQ noise source status info */
+			struct lrng_irq_info irq_info;
+			/* Serialize read of entropy pool */
+			spinlock_t lock;
+		};
+		/*
+		 * Static SHA-1 implementation in lrng_cc20_hash_buffer
+		 * processes data 64-byte-wise. Hence, ensure proper size
+		 * of LRNG entropy pool data structure.
+		 */
+		u8 hash_input_buf[LRNG_POOL_SIZE_BYTES + 64];
+	};
+};
+
+/*
+ * Implement a (modified) twisted Generalized Feedback Shift Register. (See M.
+ * Matsumoto & Y. Kurita, 1992.  Twisted GFSR generators. ACM Transactions on
+ * Modeling and Computer Simulation 2(3):179-194.  Also see M. Matsumoto & Y.
+ * Kurita, 1994.  Twisted GFSR generators II.  ACM Transactions on Modeling and
+ * Computer Simulation 4:254-266).
+ */
+static u32 const lrng_twist_table[8] = {
+	0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
+	0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
+
+/*
+ * The polynomials for the LFSR are taken from the document "Table of Linear
+ * Feedback Shift Registers" by Roy Ward, Tim Molteno, October 26, 2007.
+ * The first polynomial is from "Primitive Binary Polynomials" by Wayne
+ * Stahnke (1973) and is primitive as well as irreducible.
+ *
+ * Note, the tap values are smaller by one compared to the documentation because
+ * they are used as an index into an array where the index starts by zero.
+ *
+ * All polynomials were also checked to be primitive and irreducible with magma
+ * which ensures that the key property of the LFSR providing a compression
+ * function for entropy is guaranteed.
+ */
+static u32 const lrng_lfsr_polynomial[][4] = {
+	{ 15, 13, 12, 10 },			/* 16 words */
+	{ 31, 29, 25, 24 },			/* 32 words */
+	{ 63, 62, 60, 59 },			/* 64 words */
+	{ 127, 28, 26, 1 },			/* 128 words by Stahnke */
+	{ 255, 253, 250, 245 },			/* 256 words */
+	{ 511, 509, 506, 503 },			/* 512 words */
+	{ 1023, 1014, 1001, 1000 },		/* 1024 words */
+	{ 2047, 2034, 2033, 2028 },		/* 2048 words */
+	{ 4095, 4094, 4080, 4068 },		/* 4096 words */
+};
+
+static inline void _lrng_pool_lfsr_u32(struct lrng_pool *pool, u32 value)
+{
+	/*
+	 * Process the LFSR by altering not adjacent words but rather
+	 * more spaced apart words. Using a prime number ensures that all words
+	 * are processed evenly. As some the LFSR polynomials taps are close
+	 * together, processing adjacent words with the LSFR taps may be
+	 * inappropriate as the data just mixed-in at these taps may be not
+	 * independent from the current data to be mixed in.
+	 */
+	u32 ptr = (u32)atomic_add_return_relaxed(67, &pool->pool_ptr) &
+							(LRNG_POOL_SIZE - 1);
+	/*
+	 * Add 7 bits of rotation to the pool. At the beginning of the
+	 * pool, add an extra 7 bits rotation, so that successive passes
+	 * spread the input bits across the pool evenly.
+	 *
+	 * Note, there is a race between getting ptr and calculating
+	 * input_rotate when ptr is obtained on two or more CPUs at the
+	 * same time. This race is irrelevant as it may only come into effect
+	 * if 3 or more CPUs race at the same time which is very unlikely. If
+	 * the race happens, it applies to one event only. As this rolling
+	 * supports the LFSR without being strictly needed, we accept this
+	 * race.
+	 */
+	u32 input_rotate = (u32)atomic_add_return_relaxed((ptr ? 7 : 14),
+					&pool->input_rotate) & 31;
+	u32 word = rol32(value, input_rotate);
+
+	BUILD_BUG_ON(LRNG_POOL_WORD_BYTES != sizeof(pool->pool[0]));
+	BUILD_BUG_ON(LRNG_POOL_SIZE - 1 !=
+		     lrng_lfsr_polynomial[CONFIG_LRNG_POOL_SIZE][0]);
+	word ^= atomic_read_u32(&pool->pool[ptr]);
+	word ^= atomic_read_u32(&pool->pool[
+		(ptr + lrng_lfsr_polynomial[CONFIG_LRNG_POOL_SIZE][0]) &
+		       (LRNG_POOL_SIZE - 1)]);
+	word ^= atomic_read_u32(&pool->pool[
+		(ptr + lrng_lfsr_polynomial[CONFIG_LRNG_POOL_SIZE][1]) &
+		       (LRNG_POOL_SIZE - 1)]);
+	word ^= atomic_read_u32(&pool->pool[
+		(ptr + lrng_lfsr_polynomial[CONFIG_LRNG_POOL_SIZE][2]) &
+		       (LRNG_POOL_SIZE - 1)]);
+	word ^= atomic_read_u32(&pool->pool[
+		(ptr + lrng_lfsr_polynomial[CONFIG_LRNG_POOL_SIZE][3]) &
+		       (LRNG_POOL_SIZE - 1)]);
+
+	word = (word >> 3) ^ lrng_twist_table[word & 7];
+	atomic_set(&pool->pool[ptr], word);
+}
+
+u32 __lrng_pool_hash_df(const struct lrng_crypto_cb *crypto_cb, void *hash,
+			struct lrng_pool *pool, u8 *outbuf, u32 requested_bits);
diff --git a/drivers/char/lrng/lrng_pool.c b/drivers/char/lrng/lrng_pool.c
new file mode 100644
index 000000000000..0d4111ce7bc2
--- /dev/null
+++ b/drivers/char/lrng/lrng_pool.c
@@ -0,0 +1,589 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG Entropy pool management
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <asm/irq_regs.h>
+#include <linux/lrng.h>
+#include <linux/percpu.h>
+#include <linux/random.h>
+#include <linux/utsname.h>
+#include <linux/workqueue.h>
+
+#include "lrng_internal.h"
+#include "lrng_lfsr.h"
+
+struct lrng_state {
+	bool lrng_operational;		/* Is DRNG operational? */
+	bool lrng_fully_seeded;		/* Is DRNG fully seeded? */
+	bool lrng_min_seeded;		/* Is DRNG minimally seeded? */
+
+	/*
+	 * To ensure that external entropy providers cannot dominate the
+	 * internal noise sources but yet cannot be dominated by internal
+	 * noise sources, the following booleans are intended to allow
+	 * external to provide seed once when a DRNG reseed occurs. This
+	 * triggering of external noise source is performed even when the
+	 * entropy pool has sufficient entropy.
+	 */
+	bool lrng_seed_hw;		/* Allow HW to provide seed */
+	bool lrng_seed_user;		/* Allow user space to provide seed */
+
+	struct work_struct lrng_seed_work;	/* (re)seed work queue */
+};
+
+static struct lrng_pool lrng_pool __aligned(LRNG_KCAPI_ALIGN) = {
+	.irq_info	= {
+		.irq_entropy_bits	= LRNG_IRQ_ENTROPY_BITS,
+		.num_events_thresh	= ATOMIC_INIT(LRNG_INIT_ENTROPY_BITS +
+						LRNG_CONDITIONING_ENTROPY_LOSS),
+		/* Sample IRQ pointer data at least during boot */
+		.irq_highres_timer	= false },
+	.lock		= __SPIN_LOCK_UNLOCKED(lrng_pool.lock)
+};
+
+static struct lrng_state lrng_state = { false, false, false, true, true };
+
+/********************************** Helper ***********************************/
+
+/* External entropy provider is allowed to provide seed data */
+bool lrng_state_exseed_allow(enum lrng_external_noise_source source)
+{
+	if (source == lrng_noise_source_hw)
+		return lrng_state.lrng_seed_hw;
+	return lrng_state.lrng_seed_user;
+}
+
+/* Enable / disable external entropy provider to furnish seed */
+void lrng_state_exseed_set(enum lrng_external_noise_source source, bool type)
+{
+	if (source == lrng_noise_source_hw)
+		lrng_state.lrng_seed_hw = type;
+	else
+		lrng_state.lrng_seed_user = type;
+}
+
+static inline void lrng_state_exseed_allow_all(void)
+{
+	lrng_state_exseed_set(lrng_noise_source_hw, true);
+	lrng_state_exseed_set(lrng_noise_source_user, true);
+}
+
+void lrng_state_init_seed_work(void)
+{
+	INIT_WORK(&lrng_state.lrng_seed_work, lrng_drng_seed_work);
+}
+
+static inline u32 lrng_entropy_to_data(u32 entropy_bits)
+{
+	return ((entropy_bits * lrng_pool.irq_info.irq_entropy_bits) /
+		LRNG_DRNG_SECURITY_STRENGTH_BITS);
+}
+
+static inline u32 lrng_data_to_entropy(u32 irqnum)
+{
+	return ((irqnum * LRNG_DRNG_SECURITY_STRENGTH_BITS) /
+		lrng_pool.irq_info.irq_entropy_bits);
+}
+
+u32 lrng_avail_entropy(void)
+{
+	return min_t(u32, LRNG_POOL_SIZE_BITS, lrng_data_to_entropy(
+			atomic_read_u32(&lrng_pool.irq_info.num_events)));
+}
+
+void lrng_set_entropy_thresh(u32 new)
+{
+	atomic_set(&lrng_pool.irq_info.num_events_thresh,
+		   lrng_entropy_to_data(new));
+}
+
+/*
+ * Reading of the LRNG pool is only allowed by one caller. The reading is
+ * only performed to (re)seed DRNGs. Thus, if this "lock" is already taken,
+ * the reseeding operation is in progress. The caller is not intended to wait
+ * but continue with its other operation.
+ */
+int lrng_pool_trylock(void)
+{
+	return atomic_cmpxchg(&lrng_pool.irq_info.reseed_in_progress, 0, 1);
+}
+
+void lrng_pool_unlock(void)
+{
+	atomic_set(&lrng_pool.irq_info.reseed_in_progress, 0);
+}
+
+void lrng_reset_state(void)
+{
+	struct lrng_irq_info *irq_info = &lrng_pool.irq_info;
+
+	atomic_set(&irq_info->num_events, 0);
+	lrng_state.lrng_operational = false;
+	lrng_state.lrng_fully_seeded = false;
+	lrng_state.lrng_min_seeded = false;
+	lrng_pool.all_online_numa_node_seeded = false;
+	pr_debug("reset LRNG\n");
+}
+
+void lrng_pool_all_numa_nodes_seeded(void)
+{
+	lrng_pool.all_online_numa_node_seeded = true;
+}
+
+bool lrng_state_min_seeded(void)
+{
+	return lrng_state.lrng_min_seeded;
+}
+
+bool lrng_state_fully_seeded(void)
+{
+	return lrng_state.lrng_fully_seeded;
+}
+
+bool lrng_state_operational(void)
+{
+	return lrng_state.lrng_operational;
+}
+
+bool lrng_pool_highres_timer(void)
+{
+	return lrng_pool.irq_info.irq_highres_timer;
+}
+
+void lrng_pool_set_entropy(u32 entropy_bits)
+{
+	atomic_set(&lrng_pool.irq_info.num_events,
+		   lrng_entropy_to_data(entropy_bits));
+}
+
+static void lrng_pool_configure(bool highres_timer, u32 irq_entropy_bits)
+{
+	struct lrng_irq_info *irq_info = &lrng_pool.irq_info;
+
+	irq_info->irq_highres_timer = highres_timer;
+	if (irq_info->irq_entropy_bits != irq_entropy_bits) {
+		irq_info->irq_entropy_bits = irq_entropy_bits;
+		/* Reset the threshold based on new oversampling factor. */
+		lrng_set_entropy_thresh(atomic_read_u32(
+						&irq_info->num_events_thresh));
+	}
+}
+
+static int __init lrng_init_time_source(void)
+{
+	if (random_get_entropy() || random_get_entropy()) {
+		/*
+		 * As the highres timer is identified here, previous interrupts
+		 * obtained during boot time are treated like a lowres-timer
+		 * would have been present.
+		 */
+		lrng_pool_configure(true, LRNG_IRQ_ENTROPY_BITS);
+	} else {
+		lrng_health_disable();
+		lrng_pool_configure(false, LRNG_IRQ_ENTROPY_BITS *
+					   LRNG_IRQ_OVERSAMPLING_FACTOR);
+		pr_warn("operating without high-resolution timer and applying IRQ oversampling factor %u\n",
+			LRNG_IRQ_OVERSAMPLING_FACTOR);
+	}
+
+	return 0;
+}
+
+core_initcall(lrng_init_time_source);
+
+/* invoke function with buffer aligned to 4 bytes */
+void lrng_pool_lfsr(const u8 *buf, u32 buflen)
+{
+	u32 *p_buf = (u32 *)buf;
+
+	for (; buflen >= 4; buflen -= 4)
+		lrng_pool_lfsr_u32(*p_buf++);
+
+	buf = (u8 *)p_buf;
+	while (buflen--)
+		lrng_pool_lfsr_u32(*buf++);
+}
+
+void lrng_pool_lfsr_nonaligned(const u8 *buf, u32 buflen)
+{
+	while (buflen) {
+		if (!((unsigned long)buf & (sizeof(u32) - 1))) {
+			lrng_pool_lfsr(buf, buflen);
+			return;
+		}
+
+		lrng_pool_lfsr_u32(*buf++);
+		buflen--;
+	}
+}
+
+/**************************** Interrupt processing ****************************/
+
+/*
+ * Hot code path - inject data into entropy pool using LFSR
+ */
+void lrng_pool_lfsr_u32(u32 value)
+{
+	_lrng_pool_lfsr_u32(&lrng_pool, value);
+}
+
+/*
+ * Hot code path - mix data into entropy pool
+ */
+void lrng_pool_add_irq(u32 irq_num)
+{
+	struct lrng_irq_info *irq_info = &lrng_pool.irq_info;
+
+	atomic_add(irq_num, &irq_info->num_events);
+
+	/*
+	 * Once all DRNGs are fully seeded, the interrupt noise
+	 * sources will not trigger any reseeding any more.
+	 */
+	if (likely(lrng_pool.all_online_numa_node_seeded))
+		return;
+
+	/* Only try to reseed if the DRNG is alive. */
+	if (!lrng_get_available())
+		return;
+
+	/* Only trigger the DRNG reseed if we have collected enough IRQs. */
+	if (atomic_read_u32(&lrng_pool.irq_info.num_events) <
+	    atomic_read_u32(&lrng_pool.irq_info.num_events_thresh))
+		return;
+
+	/* Ensure that the seeding only occurs once at any given time. */
+	if (lrng_pool_trylock())
+		return;
+
+	/* Seed the DRNG with IRQ noise. */
+	schedule_work(&lrng_state.lrng_seed_work);
+}
+
+void lrng_pool_add_entropy(u32 entropy_bits)
+{
+	lrng_pool_add_irq(lrng_entropy_to_data(entropy_bits));
+}
+
+/*
+ * Generate a hashed output of pool using the SP800-90A section 10.3.1 hash_df
+ * function
+ */
+u32 __lrng_pool_hash_df(const struct lrng_crypto_cb *crypto_cb, void *hash,
+			struct lrng_pool *pool, u8 *outbuf, u32 requested_bits)
+{
+	u32 digestsize, requested_bytes = requested_bits >> 3,
+	    generated_bytes = 0;
+	u8 digest[64] __aligned(LRNG_KCAPI_ALIGN);
+
+	digestsize = crypto_cb->lrng_hash_digestsize(hash);
+	if (digestsize > sizeof(digest)) {
+		pr_err("Digest buffer too small\n");
+		return 0;
+	}
+
+	pool->counter = 1;
+	pool->requested_bits = cpu_to_be32(requested_bytes << 3);
+
+	while (requested_bytes) {
+		u32 tocopy = min_t(u32, requested_bytes, digestsize);
+
+		/* The counter must not wrap */
+		if (pool->counter == 0)
+			goto out;
+
+		if (crypto_cb->lrng_hash_buffer(hash, (u8 *)pool,
+						LRNG_POOL_SIZE_BYTES + 64,
+						digest))
+			goto out;
+
+		/* Copy the data out to the caller */
+		memcpy(outbuf + generated_bytes, digest, tocopy);
+		requested_bytes -= tocopy;
+		generated_bytes += tocopy;
+		pool->counter++;
+	}
+
+out:
+	/* Mix read data back into pool for backtracking resistance */
+	if (generated_bytes)
+		lrng_pool_lfsr(outbuf, generated_bytes);
+	memzero_explicit(digest, digestsize);
+	return (generated_bytes<<3);
+}
+
+static inline u32 lrng_pool_hash_df(const struct lrng_crypto_cb *crypto_cb,
+				    void *hash, u8 *outbuf, u32 requested_bits)
+{
+	return __lrng_pool_hash_df(crypto_cb, hash, &lrng_pool, outbuf,
+				   requested_bits);
+}
+
+/**
+ * lrng_get_pool() - Read the entropy pool out for use.
+ *
+ * This function handles the translation from the number of received interrupts
+ * into an entropy statement. The conversion depends on LRNG_IRQ_ENTROPY_BITS
+ * which defines how many interrupts must be received to obtain 256 bits of
+ * entropy. With this value, the function lrng_data_to_entropy converts a given
+ * data size (received interrupts, requested amount of data, etc.) into an
+ * entropy statement. lrng_entropy_to_data does the reverse.
+ *
+ * Both functions are agnostic about the type of data: when the number of
+ * interrupts is processed by these functions, the resulting entropy value is in
+ * bits as we assume the entropy of interrupts is measured in bits. When data is
+ * processed, the entropy value is in bytes as the data is measured in bytes.
+ *
+ * @outbuf: buffer to store data in with size LRNG_DRNG_SECURITY_STRENGTH_BYTES
+ * @requested_entropy_bits: requested bits of entropy -- the function will
+ *			    return at least this amount of entropy if available
+ * @entropy_retain: amount of entropy in bits that should be left in the pool
+ *
+ * Return: estimated entropy from the IRQs that was obtained
+ */
+static u32 lrng_get_pool(const struct lrng_crypto_cb *crypto_cb, void *hash,
+			 u8 *outbuf, u32 requested_entropy_bits,
+			 u32 entropy_retain)
+{
+	struct lrng_pool *pool = &lrng_pool;
+	struct lrng_state *state = &lrng_state;
+	struct lrng_irq_info *irq_info = &pool->irq_info;
+	unsigned long flags;
+
+	u32 irq_num_events_used, irq_num_events, avail_entropy_bits;
+
+	/* This get_pool operation must only be called once at a given time! */
+	spin_lock_irqsave(&pool->lock, flags);
+
+	/* How many unused interrupts are in entropy pool? */
+	irq_num_events = atomic_read_u32(&irq_info->num_events);
+	/* Convert available interrupts into entropy statement */
+	avail_entropy_bits = lrng_data_to_entropy(irq_num_events);
+
+	/* Cap available entropy to pool size */
+	avail_entropy_bits =
+			min_t(u32, avail_entropy_bits, LRNG_POOL_SIZE_BITS);
+
+	/* How much entropy we need to and can we use? */
+	if (unlikely(!state->lrng_fully_seeded)) {
+		/*
+		 * During boot time, we read 256 bits data with
+		 * avail_entropy_bits entropy. In case our conservative
+		 * entropy estimate underestimates the available entropy
+		 * we can transport as much available entropy as
+		 * possible. The entropy pool does not operate compliant to
+		 * the German AIS 21/31 NTG.1 yet.
+		 */
+		requested_entropy_bits =
+				LRNG_DRNG_SECURITY_STRENGTH_BITS;
+	} else {
+		/* Provide all entropy above retaining level */
+		if (avail_entropy_bits < entropy_retain) {
+			requested_entropy_bits = 0;
+			goto out;
+		}
+		avail_entropy_bits -= entropy_retain;
+		requested_entropy_bits = min_t(u32, avail_entropy_bits,
+					       requested_entropy_bits);
+	}
+
+	/* Hash is a compression function: we generate entropy amount of data */
+	requested_entropy_bits = round_down(requested_entropy_bits, 8);
+
+	requested_entropy_bits = lrng_pool_hash_df(crypto_cb, hash, outbuf,
+						   requested_entropy_bits);
+
+	/* Boot time: After getting the full buffer adjust the entropy value. */
+	requested_entropy_bits = min_t(u32, avail_entropy_bits,
+				       requested_entropy_bits);
+
+out:
+	/* Convert used entropy into interrupt number for subtraction */
+	irq_num_events_used = lrng_entropy_to_data(requested_entropy_bits);
+
+	/*
+	 * The hash_df operation entropy assessment shows that the output
+	 * entropy is one bit smaller than the input entropy. Therefore we
+	 * account for this one bit of entropy here: if we have sufficient
+	 * entropy in the LFSR, we say we used one bit of entropy more.
+	 * Otherwise we reduce the amount of entropy we say we generated with
+	 * the hash_df.
+	 */
+	if (irq_num_events_used) {
+		if ((irq_num_events_used + LRNG_CONDITIONING_ENTROPY_LOSS) <=
+		    lrng_entropy_to_data(avail_entropy_bits)) {
+			irq_num_events_used += LRNG_CONDITIONING_ENTROPY_LOSS;
+		} else {
+			if (unlikely(requested_entropy_bits <
+				     LRNG_CONDITIONING_ENTROPY_LOSS))
+				requested_entropy_bits = 0;
+			else
+				requested_entropy_bits -=
+						LRNG_CONDITIONING_ENTROPY_LOSS;
+		}
+	}
+
+	/*
+	 * New events might have arrived in the meanwhile and we don't
+	 * want to throw them away unconditionally. On the other hand,
+	 * these new events might have been mixed in before
+	 * lrng_hash_df_pool() had been able to draw any entropy
+	 * from the pool and thus, the pool capacity might have been
+	 * exceeded at some point. Note that in theory, some events
+	 * might get lost inbetween the atomic_read() and
+	 * atomic_set() below. But that's fine, because it's no real
+	 * concern while code preventing this would come at the cost of
+	 * additional complexity. Likewise, some events which arrived
+	 * after full or partial completion of the __lrng_hash_df_pool()
+	 * above might get unnecessarily thrown away by the min()
+	 * operation below; the same argument applies there.
+	 */
+	irq_num_events = atomic_read_u32(&irq_info->num_events);
+	irq_num_events = min_t(u32, irq_num_events,
+			       lrng_entropy_to_data(LRNG_POOL_SIZE_BITS));
+	irq_num_events -= irq_num_events_used;
+	atomic_set(&irq_info->num_events, irq_num_events);
+
+	spin_unlock_irqrestore(&pool->lock, flags);
+
+	/* Obtain entropy statement in bits from the used entropy */
+	pr_debug("obtained %u bits of entropy from %u newly collected interrupts - not using %u interrupts\n",
+		 requested_entropy_bits, irq_num_events_used,
+		 irq_num_events);
+
+	return requested_entropy_bits;
+}
+
+/* Fill the seed buffer with data from the noise sources */
+int lrng_fill_seed_buffer(const struct lrng_crypto_cb *crypto_cb, void *hash,
+			  struct entropy_buf *entropy_buf, u32 entropy_retain)
+{
+	struct lrng_state *state = &lrng_state;
+	u32 total_entropy_bits = 0;
+
+	/* Require at least 128 bits of entropy for any reseed. */
+	if (state->lrng_fully_seeded &&
+	    (lrng_avail_entropy() <
+	     lrng_slow_noise_req_entropy(LRNG_MIN_SEED_ENTROPY_BITS +
+					 LRNG_CONDITIONING_ENTROPY_LOSS) +
+	      entropy_retain))
+		goto wakeup;
+
+	/*
+	 * Concatenate the output of the noise sources. This would be the
+	 * spot to add an entropy extractor logic if desired. Note, this
+	 * has the ability to collect entropy equal or larger than the DRNG
+	 * strength.
+	 */
+	total_entropy_bits = lrng_get_pool(crypto_cb, hash, entropy_buf->a,
+					   LRNG_DRNG_SECURITY_STRENGTH_BITS,
+					   entropy_retain);
+	total_entropy_bits += lrng_get_arch(entropy_buf->b);
+	total_entropy_bits += lrng_get_jent(entropy_buf->c,
+					    LRNG_DRNG_SECURITY_STRENGTH_BYTES);
+
+	/* also reseed the DRNG with the current time stamp */
+	entropy_buf->now = random_get_entropy();
+
+	/* allow external entropy provider to provide seed */
+	lrng_state_exseed_allow_all();
+
+wakeup:
+	/*
+	 * Shall we wake up user space writers? This location covers
+	 * ensures that the user space provider does not dominate the internal
+	 * noise sources since in case the first call of this function finds
+	 * sufficient entropy in the entropy pool, it will not trigger the
+	 * wakeup. This implies that when the next /dev/urandom read happens,
+	 * the entropy pool is drained.
+	 */
+	lrng_writer_wakeup();
+
+	return total_entropy_bits;
+}
+
+/**
+ * lrng_init_ops() - Set seed stages of LRNG
+ *
+ * Set the slow noise source reseed trigger threshold. The initial threshold
+ * is set to the minimum data size that can be read from the pool: a word. Upon
+ * reaching this value, the next seed threshold of 128 bits is set followed
+ * by 256 bits.
+ *
+ * @entropy_bits: size of entropy currently injected into DRNG
+ */
+void lrng_init_ops(u32 seed_bits)
+{
+	struct lrng_state *state = &lrng_state;
+
+	if (state->lrng_operational)
+		return;
+
+	/* DRNG is seeded with full security strength */
+	if (state->lrng_fully_seeded) {
+		state->lrng_operational = lrng_sp80090b_startup_complete();
+		lrng_process_ready_list();
+		lrng_init_wakeup();
+	} else if (seed_bits >= LRNG_FULL_SEED_ENTROPY_BITS) {
+		invalidate_batched_entropy();
+		state->lrng_fully_seeded = true;
+		state->lrng_operational = lrng_sp80090b_startup_complete();
+		state->lrng_min_seeded = true;
+		pr_info("LRNG fully seeded with %u bits of entropy\n",
+			seed_bits);
+		lrng_set_entropy_thresh(LRNG_FULL_SEED_ENTROPY_BITS +
+					LRNG_CONDITIONING_ENTROPY_LOSS);
+		lrng_process_ready_list();
+		lrng_init_wakeup();
+
+	} else if (!state->lrng_min_seeded) {
+
+		/* DRNG is seeded with at least 128 bits of entropy */
+		if (seed_bits >= LRNG_MIN_SEED_ENTROPY_BITS) {
+			invalidate_batched_entropy();
+			state->lrng_min_seeded = true;
+			pr_info("LRNG minimally seeded with %u bits of entropy\n",
+				seed_bits);
+			lrng_set_entropy_thresh(
+				lrng_slow_noise_req_entropy(
+					LRNG_FULL_SEED_ENTROPY_BITS +
+					LRNG_CONDITIONING_ENTROPY_LOSS));
+			lrng_process_ready_list();
+			lrng_init_wakeup();
+
+		/* DRNG is seeded with at least LRNG_INIT_ENTROPY_BITS bits */
+		} else if (seed_bits >= LRNG_INIT_ENTROPY_BITS) {
+			pr_info("LRNG initial entropy level %u bits of entropy\n",
+				seed_bits);
+			lrng_set_entropy_thresh(
+				lrng_slow_noise_req_entropy(
+					LRNG_MIN_SEED_ENTROPY_BITS +
+					LRNG_CONDITIONING_ENTROPY_LOSS));
+		}
+	}
+}
+
+int __init rand_initialize(void)
+{
+	ktime_t now_time = ktime_get_real();
+	unsigned long rand;
+	unsigned int i;
+
+	lrng_drng_init_early();
+
+	lrng_pool_lfsr_u32(now_time);
+	for (i = 0; i < LRNG_POOL_SIZE; i++) {
+		if (!arch_get_random_seed_long_early(&rand) &&
+		    !arch_get_random_long_early(&rand))
+			rand = random_get_entropy();
+		lrng_pool_lfsr((u8 *)&rand, sizeof(rand));
+	}
+	lrng_pool_lfsr_nonaligned((u8 *)utsname(), sizeof(*(utsname())));
+
+	return 0;
+}
diff --git a/drivers/char/lrng/lrng_sw_noise.c b/drivers/char/lrng/lrng_sw_noise.c
new file mode 100644
index 000000000000..b34a82ed9112
--- /dev/null
+++ b/drivers/char/lrng/lrng_sw_noise.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG Slow Noise Source: Interrupt data collection
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#include <asm/irq_regs.h>
+#include <asm/ptrace.h>
+#include <linux/random.h>
+
+#include "lrng_internal.h"
+#include "lrng_sw_noise.h"
+
+/* Holder of time stamps before mixing them into the entropy pool */
+static DEFINE_PER_CPU(u32 [LRNG_TIME_ARRAY_SIZE], lrng_time);
+static DEFINE_PER_CPU(u32, lrng_time_ptr) = 0;
+static DEFINE_PER_CPU(u8, lrng_time_irqs) = 0;
+
+/*
+ * Batching up of entropy in per-CPU array before injecting into entropy pool.
+ *
+ * The random32_data is solely to be used for the external random32 PRNG.
+ */
+static inline void lrng_time_process(u32 random32_data)
+{
+	u32 i, ptr, now_time = random_get_entropy();
+	u32 now_time_masked = now_time & LRNG_TIME_SLOTSIZE_MASK;
+	enum lrng_health_res health_test;
+
+	/* Ensure sufficient space in lrng_time_irqs */
+	BUILD_BUG_ON(LRNG_TIME_NUM_VALUES >= (1 << (sizeof(u8) << 3)));
+	BUILD_BUG_ON(LRNG_TIME_ARRAY_MEMBER_BITS % LRNG_TIME_SLOTSIZE_BITS);
+	/* Ensure consistency of values */
+	BUILD_BUG_ON(LRNG_TIME_ARRAY_MEMBER_BITS != sizeof(lrng_time[0]) << 3);
+
+	/* During boot time, we mix the full time stamp directly into LFSR */
+	if (unlikely(!lrng_state_fully_seeded())) {
+
+		/* Seed random32 PRNG with data not used by LRNG. */
+		this_cpu_add(net_rand_state.s1, random32_data);
+
+		if (lrng_raw_hires_entropy_store(now_time))
+			goto out;
+
+		health_test = lrng_health_test(now_time);
+		if (health_test > lrng_health_fail_use)
+			goto out;
+
+		lrng_pool_lfsr_u32(now_time);
+		if (health_test == lrng_health_pass)
+			lrng_pool_add_irq(1);
+		goto out;
+	}
+
+	/* Runtime operation */
+	if (lrng_raw_hires_entropy_store(now_time_masked))
+		goto out;
+
+	/* Seed random32 PRNG with data not used by LRNG. */
+	this_cpu_add(net_rand_state.s1,
+		     (now_time & ~LRNG_TIME_SLOTSIZE_MASK) ^ random32_data);
+
+	health_test = lrng_health_test(now_time_masked);
+	if (health_test > lrng_health_fail_use)
+		goto out;
+
+	ptr = this_cpu_inc_return(lrng_time_ptr) & LRNG_TIME_WORD_MASK;
+	this_cpu_or(lrng_time[lrng_time_idx2array(ptr)],
+		    lrng_time_slot_val(now_time_masked,
+				       lrng_time_idx2slot(ptr)));
+
+	/* Interrupt delivers entropy if health test passes */
+	if (health_test == lrng_health_pass)
+		this_cpu_inc(lrng_time_irqs);
+
+	/* Only mix the buffer of time stamps into LFSR when wrapping */
+	if (ptr < LRNG_TIME_WORD_MASK)
+		goto out;
+
+	for (i = 0; i < LRNG_TIME_ARRAY_SIZE; i++) {
+		if (lrng_raw_array_entropy_store(this_cpu_read(lrng_time[i]))) {
+			/*
+			 * If we fed even a part of the array to external
+			 * analysis, we mark that the entire array has no
+			 * entropy. This is due to the non-IID property of
+			 * the data as we do not fully know whether the
+			 * existing dependencies diminish the entropy beyond
+			 * to what we expect it has.
+			 */
+			this_cpu_write(lrng_time_irqs, 0);
+		} else {
+			lrng_pool_lfsr_u32(this_cpu_read(lrng_time[i]));
+		}
+
+		this_cpu_write(lrng_time[i], 0);
+	}
+	lrng_pool_add_irq(this_cpu_read(lrng_time_irqs));
+	this_cpu_write(lrng_time_irqs, 0);
+
+out:
+	lrng_perf_time(now_time);
+}
+
+/*
+ * Hot code path - Callback for interrupt handler
+ */
+void add_interrupt_randomness(int irq, int irq_flags)
+{
+	if (lrng_pool_highres_timer()) {
+		lrng_time_process(
+			(lrng_raw_irq_entropy_store(irq) ? 0 : irq) ^
+			(lrng_raw_irqflags_entropy_store(irq_flags) ? 0 :
+								irq_flags) ^
+			(lrng_raw_retip_entropy_store(_RET_IP_) ? 0 :
+								  _RET_IP_));
+	} else {
+		struct pt_regs *regs = get_irq_regs();
+		static atomic_t reg_idx = ATOMIC_INIT(0);
+		u64 ip;
+
+		if (regs) {
+			u32 *ptr = (u32 *)regs;
+			int reg_ptr = atomic_add_return_relaxed(1, &reg_idx);
+			size_t n = (sizeof(struct pt_regs) / sizeof(u32));
+
+			ip = instruction_pointer(regs);
+			lrng_pool_lfsr_u32(*(ptr + (reg_ptr % n)));
+
+			lrng_time_process(
+				lrng_raw_retip_entropy_store(_RET_IP_) ? 0 :
+								_RET_IP_);
+		} else {
+			ip = _RET_IP_;
+
+			lrng_time_process(0);
+		}
+
+		/*
+		 * The XOR operation combining the different values is not
+		 * considered to destroy entropy since the entirety of all
+		 * processed values delivers the entropy (and not each
+		 * value separately of the other values).
+		 */
+		lrng_pool_lfsr_u32(
+			(lrng_raw_jiffies_entropy_store(jiffies) ? 0 :
+								   jiffies) ^
+			(lrng_raw_irq_entropy_store(irq) ? 0 : irq) ^
+			(lrng_raw_irqflags_entropy_store(irq_flags) ? 0 :
+								irq_flags) ^
+			(ip >> 32) ^
+			(lrng_raw_retip_entropy_store(ip) ? 0 : ip));
+	}
+}
+EXPORT_SYMBOL(add_interrupt_randomness);
diff --git a/drivers/char/lrng/lrng_sw_noise.h b/drivers/char/lrng/lrng_sw_noise.h
new file mode 100644
index 000000000000..919d8c368991
--- /dev/null
+++ b/drivers/char/lrng/lrng_sw_noise.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * LRNG Slow Noise Source: Time stamp array handling
+ *
+ * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+/*
+ * To limit the impact on the interrupt handling, the LRNG concatenates
+ * entropic LSB parts of the time stamps in a per-CPU array and only
+ * injects them into the entropy pool when the array is full.
+ */
+
+/* Store multiple integers in one u32 */
+#define LRNG_TIME_SLOTSIZE_BITS		(8)
+#define LRNG_TIME_SLOTSIZE_MASK		((1 << LRNG_TIME_SLOTSIZE_BITS) - 1)
+#define LRNG_TIME_ARRAY_MEMBER_BITS	(4 << 3) /* ((sizeof(u32)) << 3) */
+#define LRNG_TIME_SLOTS_PER_UINT	(LRNG_TIME_ARRAY_MEMBER_BITS / \
+					 LRNG_TIME_SLOTSIZE_BITS)
+
+/*
+ * Number of time values to store in the array - in small environments
+ * only one atomic_t variable per CPU is used.
+ */
+#define LRNG_TIME_NUM_VALUES		(CONFIG_BASE_SMALL ?		\
+					 LRNG_TIME_SLOTS_PER_UINT : 64)
+/* Mask of LSB of time stamp to store */
+#define LRNG_TIME_WORD_MASK		(LRNG_TIME_NUM_VALUES - 1)
+
+#define LRNG_TIME_SLOTS_MASK		(LRNG_TIME_SLOTS_PER_UINT - 1)
+#define LRNG_TIME_ARRAY_SIZE		(LRNG_TIME_NUM_VALUES /	\
+					 LRNG_TIME_SLOTS_PER_UINT)
+
+/* Starting bit index of slot */
+static inline unsigned int lrng_time_slot2bitindex(unsigned int slot)
+{
+	return (LRNG_TIME_SLOTSIZE_BITS * slot);
+}
+
+/* Convert index into the array index */
+static inline unsigned int lrng_time_idx2array(unsigned int idx)
+{
+	return idx / LRNG_TIME_SLOTS_PER_UINT;
+}
+
+/* Convert index into the slot of a given array index */
+static inline unsigned int lrng_time_idx2slot(unsigned int idx)
+{
+	return idx & LRNG_TIME_SLOTS_MASK;
+}
+
+/* Convert value into slot value */
+static inline unsigned int lrng_time_slot_val(unsigned int val,
+					      unsigned int slot)
+{
+	return val << lrng_time_slot2bitindex(slot);
+}
diff --git a/include/linux/lrng.h b/include/linux/lrng.h
new file mode 100644
index 000000000000..2c3d2ed32a91
--- /dev/null
+++ b/include/linux/lrng.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * Copyright (C) 2018 - 2020, Stephan Mueller <smueller@xxxxxxxxxx>
+ */
+
+#ifndef _LRNG_H
+#define _LRNG_H
+
+#include <linux/errno.h>
+#include <linux/types.h>
+
+/**
+ * struct lrng_crypto_cb - cryptographic callback functions
+ * @lrng_drng_name		Name of DRNG
+ * @lrng_hash_name		Name of Hash used for reading entropy pool
+ * @lrng_drng_alloc:		Allocate DRNG -- the provided integer should be
+ *				used for sanity checks.
+ *				return: allocated data structure or PTR_ERR on
+ *					error
+ * @lrng_drng_dealloc:		Deallocate DRNG
+ * @lrng_drng_seed_helper:	Seed the DRNG with data of arbitrary length
+ *				drng: is pointer to data structure allocated
+ *				      with lrng_drng_alloc
+ *				return: >= 0 on success, < 0 on error
+ * @lrng_drng_generate_helper:	Generate random numbers from the DRNG with
+ *				arbitrary length
+ * @lrng_hash_alloc:		Allocate the hash for reading the entropy pool
+ *				return: allocated data structure (NULL is
+ *					success too) or ERR_PTR on error
+ * @lrng_hash_dealloc:		Deallocate Hash
+ * @lrng_hash_digestsize:	Return the digestsize for the used hash to read
+ *				out entropy pool
+ *				hash: is pointer to data structure allocated
+ *				      with lrng_hash_alloc
+ *				return: size of digest of hash in bytes
+ * @lrng_hash_buffer:		Generate hash
+ *				hash: is pointer to data structure allocated
+ *				      with lrng_hash_alloc
+ *				return: 0 on success, < 0 on error
+ */
+struct lrng_crypto_cb {
+	const char *(*lrng_drng_name)(void);
+	const char *(*lrng_hash_name)(void);
+	void *(*lrng_drng_alloc)(u32 sec_strength);
+	void (*lrng_drng_dealloc)(void *drng);
+	int (*lrng_drng_seed_helper)(void *drng, const u8 *inbuf, u32 inbuflen);
+	int (*lrng_drng_generate_helper)(void *drng, u8 *outbuf, u32 outbuflen);
+	void *(*lrng_hash_alloc)(const u8 *key, u32 keylen);
+	void (*lrng_hash_dealloc)(void *hash);
+	u32 (*lrng_hash_digestsize)(void *hash);
+	int (*lrng_hash_buffer)(void *hash, const u8 *inbuf, u32 inbuflen,
+				u8 *digest);
+};
+
+/* Register cryptographic backend */
+#ifdef CONFIG_LRNG_DRNG_SWITCH
+int lrng_set_drng_cb(const struct lrng_crypto_cb *cb);
+#else	/* CONFIG_LRNG_DRNG_SWITCH */
+static inline int
+lrng_set_drng_cb(const struct lrng_crypto_cb *cb) { return -EOPNOTSUPP; }
+#endif	/* CONFIG_LRNG_DRNG_SWITCH */
+
+#endif /* _LRNG_H */
-- 
2.26.2