[PATCH v2 3/6] crypto: Linux Random Number Generator

[Stephan Mueller]

The LRNG with all its properties is documented in [1]. This
documentation covers the functional discussion as well as testing of all
aspects of entropy processing. In addition, the documentation explains
the conducted regression tests to verify that the LRNG is API and ABI
compatible with the legacy /dev/random implementation.

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

Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
---
 crypto/lrng.c | 1743 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1743 insertions(+)
 create mode 100644 crypto/lrng.c

diff --git a/crypto/lrng.c b/crypto/lrng.c
new file mode 100644
index 0000000..b27ac81
--- /dev/null
+++ b/crypto/lrng.c
@@ -0,0 +1,1743 @@
+/*
+ * Linux Random Number Generator (LRNG)
+ *
+ * Documentation and test code: http://www.chronox.de/lrng.html
+ *
+ * Copyright (C) 2016, Stephan Mueller <smueller@xxxxxxxxxx>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, and the entire permission notice in its entirety,
+ *    including the disclaimer of warranties.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU General Public License, in which case the provisions of the GPL2
+ * are required INSTEAD OF the above restrictions.  (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
+ * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+ * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+#include <linux/timex.h>
+#include <linux/percpu.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/spinlock.h>
+#include <linux/kthread.h>
+#include <linux/random.h>
+#include <linux/workqueue.h>
+#include <linux/poll.h>
+#include <linux/cryptohash.h>
+#include <linux/syscalls.h>
+
+#include <crypto/drbg.h>
+
+/* debug macro */
+#define DRIVER_NAME "lrng"
+#if 0
+#define dbg(fmt, ...) pr_info(DRIVER_NAME": " fmt, ##__VA_ARGS__)
+#else
+#define dbg(fmt, ...)
+#endif
+
+/*
+ * Define one DRBG out of each type with 256 bits of security strength.
+ *
+ * This definition is allowed to be changed.
+ */
+#ifdef CONFIG_CRYPTO_DRBG_HMAC
+# if 0
+#  define LRNG_DRBG_BLOCKLEN_BYTES 64
+#  define LRNG_DRBG_SECURITY_STRENGTH_BYTES 32
+#  define LRNG_DRBG_CORE "drbg_nopr_hmac_sha512"	/* HMAC DRBG SHA-512 */
+# else
+#  define LRNG_DRBG_BLOCKLEN_BYTES 32
+#  define LRNG_DRBG_SECURITY_STRENGTH_BYTES 32
+#  define LRNG_DRBG_CORE "drbg_nopr_hmac_sha256"	/* HMAC DRBG SHA-256 */
+# endif
+#elif defined CONFIG_CRYPTO_DRBG_HASH
+# if 0
+#  define LRNG_DRBG_BLOCKLEN_BYTES 64
+#  define LRNG_DRBG_SECURITY_STRENGTH_BYTES 32
+#  define LRNG_DRBG_CORE "drbg_nopr_sha512"		/* Hash DRBG SHA-512 */
+# else
+#  define LRNG_DRBG_BLOCKLEN_BYTES 32
+#  define LRNG_DRBG_SECURITY_STRENGTH_BYTES 32
+#  define LRNG_DRBG_CORE "drbg_nopr_sha256"		/* Hash DRBG SHA-256 */
+# endif
+#elif defined CONFIG_CRYPTO_DRBG_CTR
+# define LRNG_DRBG_BLOCKLEN_BYTES 16
+# define LRNG_DRBG_SECURITY_STRENGTH_BYTES 32
+# define LRNG_DRBG_CORE "drbg_nopr_ctr_aes256"		/* CTR DRBG AES-256 */
+#else
+# error "LRNG requires the presence of a DRBG"
+#endif
+
+/* Primary DRBG state handle */
+struct lrng_pdrbg {
+	struct drbg_state *pdrbg;	/* DRBG handle */
+	bool pdrbg_fully_seeded;	/* Is DRBG fully seeded? */
+	bool pdrbg_min_seeded;		/* Is DRBG minimally seeded? */
+	u32 pdrbg_entropy_bits;		/* Is DRBG entropy level */
+	struct work_struct lrng_seed_work;	/* (re)seed work queue */
+};
+
+/* Secondary DRBG state handle */
+struct lrng_sdrbg {
+	struct drbg_state *sdrbg;	/* DRBG handle */
+	atomic_t requests;		/* Number of DRBG requests */
+	unsigned long last_seeded;	/* Last time it was seeded */
+};
+
+#define LRNG_DRBG_BLOCKLEN_BITS (LRNG_DRBG_BLOCKLEN_BYTES * 8)
+#define LRNG_DRBG_SECURITY_STRENGTH_BITS (LRNG_DRBG_SECURITY_STRENGTH_BYTES * 8)
+
+/*
+ * SP800-90A defines a maximum request size of 1<<16 bytes. The given value is
+ * considered a safer margin. This applies to secondary DRBG.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_DRBG_MAX_REQSIZE (1<<12)
+
+/*
+ * SP800-90A defines a maximum number of requests between reseeds of 1<<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 applies to
+ * secondary DRBG.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_DRBG_RESEED_THRESH (1<<12)
+
+/* Status information about IRQ noise source */
+struct lrng_irq_info {
+	atomic_t num_events;	/* Number of non-stuck IRQs since last read */
+	atomic_t num_events_thresh;	/* Reseed threshold */
+	atomic_t pool_ptr;	/* Ptr into pool for next IRQ bit injection */
+	u32 irq_pool_reader;	/* Current word of pool to be read */
+	atomic_t last_time;	/* Stuck test: time of previous IRQ */
+	atomic_t last_delta;	/* Stuck test: delta of previous IRQ */
+	atomic_t last_delta2;	/* Stuck test: 2. time derivation of prev IRQ */
+	atomic_t reseed_in_progress;	/* Flag for on executing reseed */
+	atomic_t crngt_ctr;	/* FIPS 140-2 CRNGT counter */
+};
+
+/*
+ * According to FIPS 140-2 IG 9.8, our C threshold is at 3 back to back stuck
+ * values. It should be highly unlikely that we see three consecutive
+ * identical time stamps.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_FIPS_CRNGT 3
+
+/*
+ * This is the entropy pool used by the slow noise source. Its size should
+ * be at least as large as the interrupt entropy estimate.
+ *
+ * LRNG_POOL_SIZE is allowed to be changed.
+ */
+struct lrng_pool {
+#define LRNG_POOL_SIZE 128
+#define LRNG_POOL_WORD_BYTES (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)
+	atomic_t pool[LRNG_POOL_SIZE];	/* Pool holing the slow noise */
+	struct lrng_irq_info irq_info;	/* IRQ noise source status info */
+};
+
+/*
+ * Number of interrupts to be recorded to assume that DRBG security strength
+ * bits of entropy are received. Dividing a DRBG security strength of 256 by
+ * this value gives the entropy value for one interrupt (i.e. a folded one bit).
+ * The default value implies that we have 256 / 288 = 0.89 bits of entropy per
+ * interrupt.
+ * Note: a value below the DRBG security strength should not be defined as this
+ *	 may imply the DRBG can never be fully seeded in case other noise
+ *	 sources are unavailable.
+ * Note 2: This value must be multiples of LRNG_POOL_WORD_BYTES
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_IRQ_ENTROPY_BYTES \
+	(LRNG_DRBG_SECURITY_STRENGTH_BYTES + LRNG_POOL_WORD_BYTES)
+#define LRNG_IRQ_ENTROPY_BITS (LRNG_IRQ_ENTROPY_BYTES * 8)
+
+/*
+ * Leave given number of data bits in entropy pool to serve /dev/random while
+ * /dev/urandom is stressed. This value must be a multiple of
+ * LRNG_IRQ_ENTROPY_BITS to allow /dev/random to benefit from it completely.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_EMERG_POOLSIZE (LRNG_IRQ_ENTROPY_BITS * 2)
+
+/*
+ * Min required seed entropy is 112 bits as per FIPS 140-2 and AIS20/31.
+ *
+ * This value is allowed to be changed.
+ */
+#define LRNG_MIN_SEED_ENTROPY_BITS 112
+
+/*
+ * LRNG_MIN_SEED_ENTROPY_BITS rounded up to next LRNG_POOL_WORD multiple.
+ *
+ * This value must be changed with the following considerations:
+ * If LRNG_MIN_SEED_ENTROPY_BITS, LRNG_IRQ_ENTROPY_BITS or LRNG_POOL_WORD_BITS
+ * is changed, make sure LRNG_IRQ_MIN_NUM is changed such that
+ * (LRNG_MIN_SEED_ENTROPY_BITS * LRNG_IRQ_ENTROPY_BITS /
+ * LRNG_DRBG_SECURITY_STRENGTH_BITS) is rounded up to the next full
+ * LRNG_POOL_WORD_BITS multiple.
+ */
+#define LRNG_IRQ_MIN_NUM (LRNG_POOL_WORD_BITS * 4)
+
+static struct lrng_pdrbg lrng_pdrbg = { 0 };
+static DEFINE_SPINLOCK(lrng_pdrbg_lock); /* Lock for lrng_pdrbg and members */
+
+static struct lrng_sdrbg lrng_sdrbg = {	.sdrbg = NULL,
+					.requests =  ATOMIC_INIT(1),
+					.last_seeded = 0 };
+static DEFINE_SPINLOCK(lrng_sdrbg_lock); /* Lock for lrng_sdrbg and members */
+
+static struct lrng_pool lrng_pool = {
+	.irq_info = {
+		.num_events		= ATOMIC_INIT(0),
+		.num_events_thresh	= ATOMIC_INIT(LRNG_POOL_WORD_BITS),
+		.pool_ptr		= ATOMIC_INIT(0),
+		.irq_pool_reader	= 0,
+		.last_time		= ATOMIC_INIT(0),
+		.last_delta		= ATOMIC_INIT(0),
+		.last_delta2		= ATOMIC_INIT(0),
+		.reseed_in_progress	= ATOMIC_INIT(0),
+		.crngt_ctr		= ATOMIC_INIT(LRNG_FIPS_CRNGT),
+	},
+};
+
+static LIST_HEAD(lrng_ready_list);
+static DEFINE_SPINLOCK(lrng_ready_list_lock);
+
+static atomic_t lrng_pdrbg_avail = ATOMIC_INIT(0);
+static atomic_t lrng_initrng_bytes = ATOMIC_INIT(0);
+static DEFINE_SPINLOCK(lrng_init_rng_lock);	/* Lock the init RNG state */
+
+static DECLARE_WAIT_QUEUE_HEAD(lrng_read_wait);
+static DECLARE_WAIT_QUEUE_HEAD(lrng_write_wait);
+static DECLARE_WAIT_QUEUE_HEAD(lrng_pdrbg_init_wait);
+static struct fasync_struct *fasync;
+
+/*
+ * Estimated entropy of data is a 32th of LRNG_DRBG_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.
+ */
+static u32 archrandom = LRNG_DRBG_SECURITY_STRENGTH_BITS>>5;
+module_param(archrandom, uint, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+MODULE_PARM_DESC(archrandom, "Entropy in bits of 256 data bits from CPU noise source (e.g. RDRAND)");
+
+/*
+ * 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.
+ * The value is set to a fourth of the LRNG_POOL_SIZE_BITS.
+ */
+static u32 lrng_write_wakeup_bits = LRNG_POOL_SIZE_BITS / 4;
+
+/*
+ * The minimum number of bits of entropy before we wake up a read on
+ * /dev/random.  Should be enough to do a significant reseed where
+ * it is technically possible that the entropy estimate is to be above the
+ * DRBG security strength.
+ */
+static u32 lrng_read_wakeup_bits = LRNG_IRQ_ENTROPY_BITS;
+
+/*
+ * Maximum number of seconds between DRBG reseed intervals of the secondary
+ * DRBG. Note, this is enforced with the next request of random numbers from
+ * the secondary DRBG. Setting this value to zero implies a reseeding attempt
+ * before every generated random number.
+ */
+static int lrng_sdrbg_reseed_max_time = 600;
+
+/********************************** Helper ***********************************/
+
+static inline u32 atomic_read_u32(atomic_t *v)
+{
+	return (u32)atomic_read(v);
+}
+
+static inline u32 atomic_xchg_u32(atomic_t *v, u32 x)
+{
+	return (u32)atomic_xchg(v, x);
+}
+
+/* Is the entropy pool fill level too low and is the DRBG not fully seeded? */
+static inline bool lrng_need_entropy(void)
+{
+	return ((atomic_read_u32(&lrng_pool.irq_info.num_events) <
+		 lrng_write_wakeup_bits) &&
+		lrng_pdrbg.pdrbg_entropy_bits <
+					LRNG_DRBG_SECURITY_STRENGTH_BITS);
+}
+
+/* Is the entropy pool filled for /dev/random pull or DRBG fully seeded? */
+static inline bool lrng_have_entropy_full(void)
+{
+	return ((atomic_read_u32(&lrng_pool.irq_info.num_events) >=
+		 lrng_read_wakeup_bits) ||
+		lrng_pdrbg.pdrbg_entropy_bits >=
+					LRNG_DRBG_SECURITY_STRENGTH_BITS);
+}
+
+/*********************** Fast soise source processing ************************/
+
+/**
+ * Get CPU noise source entropy
+ *
+ * @outbuf buffer to store entropy of size LRNG_DRBG_SECURITY_STRENGTH_BYTES
+ * @return > 0 on success where value provides the added entropy in bits
+ *	   0 if no fast source was available
+ */
+static inline u32 lrng_get_arch(u8 *outbuf)
+{
+	u32 i;
+	u32 ent_bits = archrandom;
+
+	/* operate on full blocks */
+	BUILD_BUG_ON(LRNG_DRBG_SECURITY_STRENGTH_BYTES % sizeof(unsigned long));
+
+	if (!ent_bits)
+		return 0;
+
+	for (i = 0;
+	     i < (LRNG_DRBG_SECURITY_STRENGTH_BYTES / sizeof(unsigned long));
+	     i += 2) {
+		if (!arch_get_random_long((unsigned long *)outbuf)) {
+			archrandom = 0;
+			return 0;
+		}
+		outbuf += sizeof(unsigned long);
+	}
+
+	/* Obtain entropy statement -- cap entropy to buffer size in bits */
+	ent_bits = min_t(u32, ent_bits, LRNG_DRBG_SECURITY_STRENGTH_BITS);
+	dbg("obtained %u bits of entropy from CPU RNG noise source\n",
+	    ent_bits);
+	return ent_bits;
+}
+
+/************************ Slow noise source processing ************************/
+
+/**
+ * Hot code path - This function XORs all bits with each other. Effectively
+ * it calculates the parity of the given value.
+ *
+ * The implementation is taken from
+ * https://graphics.stanford.edu/~seander/bithacks.html
+ *
+ * @x value to be collapsed to one bit
+ * @return collapsed value
+ */
+static inline u32 lrng_xor_all_bits(u32 x)
+{
+	x ^= x >> 1;
+	x ^= x >> 2;
+	x = (x & 0x11111111U) * 0x11111111U;
+
+	return (x >> 28) & 1;
+}
+
+/**
+ * Hot code path - Stuck test by checking the:
+ *      1st derivation of the event occurrence (time delta)
+ *      2nd derivation of the event occurrence (delta of time deltas)
+ *      3rd derivation of the event occurrence (delta of delta of time deltas)
+ *
+ * All values must always be non-zero. This is also the FIPS 140-2 CRNGT.
+ *
+ * @irq_info Reference to IRQ information
+ * @now Event time
+ * @return 0 event occurrence not stuck (good bit)
+ *	   1 event occurrence stuck (reject bit)
+ */
+static int lrng_irq_stuck(struct lrng_irq_info *irq_info, u32 now_time)
+{
+	u32 delta = now_time - atomic_xchg_u32(&irq_info->last_time, now_time);
+	int delta2 = delta - atomic_xchg_u32(&irq_info->last_delta, delta);
+	int delta3 = delta2 - atomic_xchg(&irq_info->last_delta2, delta2);
+
+#ifdef CONFIG_CRYPTO_FIPS
+	if (fips_enabled) {
+		if (!delta) {
+			if (atomic_dec_and_test(&irq_info->crngt_ctr))
+				panic(DRIVER_NAME": FIPS 140-2 continuous random number generator test failed\n");
+		} else
+			atomic_set(&irq_info->crngt_ctr, LRNG_FIPS_CRNGT);
+	}
+#endif
+
+	if (!delta || !delta2 || !delta3)
+		return 1;
+
+	return 0;
+}
+
+/**
+ * Hot code path - mix bit into entropy pool
+ */
+static inline void lrng_mixin_bit(u32 folded_bit, u32 pool_ptr, u32 irq_num)
+{
+	pool_ptr %= LRNG_POOL_SIZE_BITS;
+
+	/*
+	 * Mix in the folded bit into the bit location pointed to by
+	 * pool_ptr. The bit location is calculated by finding the right
+	 * pool word (pool_ptr / LRNG_POOL_WORD_BITS) and the right bit
+	 * location in the word where the bit should be XORed into
+	 * (pool_ptr % LRNG_POOL_WORD_BITS).
+	 */
+	atomic_xor(folded_bit << (pool_ptr % LRNG_POOL_WORD_BITS),
+		   &lrng_pool.pool[pool_ptr / LRNG_POOL_WORD_BITS]);
+
+	/* Should we wake readers? */
+	if (irq_num == lrng_read_wakeup_bits) {
+		wake_up_interruptible(&lrng_read_wait);
+		kill_fasync(&fasync, SIGIO, POLL_IN);
+	}
+
+	/*
+	 * Once the primary DRBG is fully seeded, the interrupt noise sources
+	 * will not trigger any reseeding any more.
+	 */
+	if (lrng_pdrbg.pdrbg_fully_seeded)
+		return;
+
+	/* Only trigger the DRBG 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;
+
+	/* Only try to reseed if the DRBG is alive. */
+	if (!atomic_read(&lrng_pdrbg_avail))
+		return;
+
+	/* Ensure that the seeding only occurs once at any given time. */
+	if (atomic_cmpxchg(&lrng_pool.irq_info.reseed_in_progress, 0, 1))
+		return;
+
+	/* Seed the DRBG with IRQ noise. */
+	schedule_work(&lrng_pdrbg.lrng_seed_work);
+}
+
+/**
+ * Hot code path - Callback for interrupt handler triggering entropy collection.
+ */
+void lrng_irq_process(void)
+{
+	u32 now_time = random_get_entropy();
+	struct lrng_irq_info *irq_info = &lrng_pool.irq_info;
+	u32 folded_bit = lrng_xor_all_bits(now_time);
+	u32 pool_ptr, irq_num = 0;
+
+	/*
+	 * If obtained measurement is not stuck, advance pool_ptr to XOR
+	 * new folded bit into new location.
+	 */
+	if (!lrng_irq_stuck(irq_info, now_time)) {
+		pool_ptr = (u32)atomic_add_return(1, &irq_info->pool_ptr);
+		irq_num = (u32)atomic_add_return(1, &irq_info->num_events);
+	} else
+		pool_ptr = atomic_read_u32(&irq_info->pool_ptr);
+
+	lrng_mixin_bit(folded_bit, pool_ptr, irq_num);
+}
+EXPORT_SYMBOL(lrng_irq_process);
+
+/**
+ * Callback for HID layer
+ */
+void add_input_randomness(unsigned int type, unsigned int code,
+			  unsigned int value)
+{
+	static unsigned char last_value;
+	u32 folded_bit, pool_ptr;
+
+	/* ignore autorepeat and the like */
+	if (value == last_value)
+		return;
+
+	last_value = value;
+
+	folded_bit =
+		lrng_xor_all_bits((type << 4) ^ code ^ (code >> 4) ^ value);
+	pool_ptr = atomic_read_u32(&lrng_pool.irq_info.pool_ptr);
+
+	lrng_mixin_bit(folded_bit, pool_ptr, 0);
+}
+EXPORT_SYMBOL_GPL(add_input_randomness);
+
+/**
+ * Read the entropy pool out for use. The caller must ensure this function
+ * is only called once at a time. "noinline" needed for SystemTap testing.
+ *
+ * @outbuf buffer to store data in
+ * @outbuflen size of outbuf -- if not multiple of LRNG_POOL_WORD_BITS we will
+ *	      return a number of bits rounded down to nearest
+ *	      LRNG_POOL_WORD_BITS
+ * @requested_entropy_bits requested bits of entropy -- the function will return
+ *			   at least this amount of entropy if available
+ * @drain boolean indicating that that all entropy of pool can be used
+ *	  (otherwise some emergency amount of entropy is left)
+ * @return estimated entropy from the IRQs that went into the pool since last
+ *	   readout.
+ */
+static noinline u32 lrng_get_pool(u8 *outbuf, u32 outbuflen,
+				  u32 requested_entropy_bits, bool drain)
+{
+	u32 i, irq_num_events_used, irq_num_event_back, ent_bits, words_to_copy;
+	/* How many interrupts are in buffer? */
+	u32 irq_num_events = atomic_xchg_u32(&lrng_pool.irq_info.num_events, 0);
+
+	irq_num_events = min_t(u32, irq_num_events, LRNG_POOL_SIZE_BITS);
+
+	/* Translate requested entropy bits into data bits */
+	requested_entropy_bits = (requested_entropy_bits *
+				  LRNG_IRQ_ENTROPY_BITS) /
+				 LRNG_DRBG_SECURITY_STRENGTH_BITS;
+	/* Round up such that we are able to collect requested entropy */
+	requested_entropy_bits += LRNG_POOL_WORD_BITS - 1;
+
+	/* How many interrupts do we need to and can we use? */
+	BUILD_BUG_ON(LRNG_EMERG_POOLSIZE % LRNG_IRQ_ENTROPY_BITS);
+	if (drain)
+		irq_num_events_used = min_t(u32, irq_num_events,
+					    requested_entropy_bits);
+	else
+		irq_num_events_used = min_t(u32,
+					    (irq_num_events -
+			 min_t(u32, LRNG_EMERG_POOLSIZE, irq_num_events)),
+					    requested_entropy_bits);
+	/* Translate entropy in number of complete words to be read */
+	words_to_copy = irq_num_events_used / LRNG_POOL_WORD_BITS;
+	irq_num_events_used = words_to_copy * LRNG_POOL_WORD_BITS;
+	BUG_ON(irq_num_events_used > outbuflen<<3);
+
+	/* Read out the words from the pool */
+	for (i = lrng_pool.irq_info.irq_pool_reader;
+	     i < (lrng_pool.irq_info.irq_pool_reader + words_to_copy); i++) {
+		BUILD_BUG_ON(LRNG_POOL_SIZE_BYTES % sizeof(atomic_t));
+		/* write the result from atomic_read directly into buffer */
+		*((u32 *)outbuf) =
+			atomic_read(&lrng_pool.pool[(i % LRNG_POOL_SIZE)]);
+		outbuf += sizeof(atomic_t);
+	}
+
+	/* SystemTap: IRQ Raw Entropy Hook line */
+	/* There may be new events that came in while we processed this logic */
+	irq_num_events += atomic_xchg_u32(&lrng_pool.irq_info.num_events, 0);
+	/* Cap the number of events we say we have left to not reuse events */
+	irq_num_event_back = min_t(u32, irq_num_events - irq_num_events_used,
+				   LRNG_POOL_SIZE_BITS - irq_num_events_used);
+	/* Add the unused interrupt number back to the state variable */
+	atomic_add(irq_num_event_back, &lrng_pool.irq_info.num_events);
+
+	/* Advance the read pointer */
+	lrng_pool.irq_info.irq_pool_reader += words_to_copy;
+	lrng_pool.irq_info.irq_pool_reader %= LRNG_POOL_SIZE;
+
+	/* Turn event numbers into entropy statement */
+	ent_bits = min_t(int, LRNG_POOL_SIZE_BITS,
+		((irq_num_events_used * LRNG_DRBG_SECURITY_STRENGTH_BITS) /
+		 LRNG_IRQ_ENTROPY_BITS));
+	dbg("obtained %u bits of entropy from newly collected interrupts - not using %u interrupts\n",
+	    ent_bits, irq_num_event_back);
+	return ent_bits;
+}
+
+/****************************** DRBG processing *******************************/
+
+/* Helper to seed the DRBG */
+static inline int lrng_drbg_seed_helper(struct drbg_state *drbg,
+					const u8 *inbuf, u32 inbuflen)
+{
+	LIST_HEAD(seedlist);
+	struct drbg_string data;
+
+	drbg_string_fill(&data, inbuf, inbuflen);
+	list_add_tail(&data.list, &seedlist);
+	return drbg->d_ops->update(drbg, &seedlist, drbg->seeded);
+}
+
+/* Helper to generate random numbers from the DRBG */
+static inline int lrng_drbg_generate_helper(struct drbg_state *drbg, u8 *outbuf,
+					    u32 outbuflen)
+{
+	return drbg->d_ops->generate(drbg, outbuf, outbuflen, NULL);
+}
+
+/**
+ * Ping all kernel internal callers waiting until the DRBG is fully
+ * seeded that the DRBG is now fully seeded.
+ */
+static void lrng_process_ready_list(void)
+{
+	unsigned long flags;
+	struct random_ready_callback *rdy, *tmp;
+
+	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);
+}
+
+/**
+ * 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 112 bits is set followed
+ * by 256 bits.
+ *
+ * @entropy_bits size of entropy currently injected into DRBG
+ */
+static void lrng_pdrbg_init_ops(u32 entropy_bits)
+{
+	if (lrng_pdrbg.pdrbg_fully_seeded)
+		return;
+
+	BUILD_BUG_ON(LRNG_IRQ_MIN_NUM % LRNG_POOL_WORD_BITS);
+	BUILD_BUG_ON((LRNG_MIN_SEED_ENTROPY_BITS * LRNG_IRQ_ENTROPY_BITS /
+		     LRNG_DRBG_SECURITY_STRENGTH_BITS) > LRNG_IRQ_MIN_NUM);
+
+	/* DRBG is seeded with full security strength */
+	if (entropy_bits >= LRNG_DRBG_SECURITY_STRENGTH_BITS) {
+		lrng_pdrbg.pdrbg_fully_seeded = true;
+		lrng_pdrbg.pdrbg_min_seeded = true;
+		pr_info(DRIVER_NAME": primary DRBG fully seeded\n");
+		lrng_process_ready_list();
+		wake_up_all(&lrng_pdrbg_init_wait);
+	} else if (!lrng_pdrbg.pdrbg_min_seeded) {
+		/* DRBG is seeded with at least 112 bits of entropy */
+		if (entropy_bits >= LRNG_MIN_SEED_ENTROPY_BITS) {
+			lrng_pdrbg.pdrbg_min_seeded = true;
+			pr_info(DRIVER_NAME": primary DRBG minimally seeded\n");
+			atomic_set(&lrng_pool.irq_info.num_events_thresh,
+				   LRNG_IRQ_ENTROPY_BITS);
+		/* DRBG is seeded with at least LRNG_POOL_WORD_BITS data bits */
+		} else if (entropy_bits >= (LRNG_POOL_WORD_BITS *
+					    LRNG_DRBG_SECURITY_STRENGTH_BITS) /
+					   LRNG_IRQ_ENTROPY_BITS) {
+			pr_info(DRIVER_NAME": primary DRBG initially seeded\n");
+			atomic_set(&lrng_pool.irq_info.num_events_thresh,
+				   LRNG_IRQ_MIN_NUM);
+		}
+	}
+}
+
+/* Caller must hold lrng_pdrbg_lock */
+static int lrng_pdrbg_generate(u8 *outbuf, u32 outbuflen, bool fullentropy)
+{
+	struct drbg_state *drbg = lrng_pdrbg.pdrbg;
+	int ret;
+
+	/* /dev/random only works from a fully seeded DRBG */
+	if (fullentropy && !lrng_pdrbg.pdrbg_fully_seeded)
+		return 0;
+
+	/*
+	 * Only deliver as many bytes as the DRBG is seeded with except during
+	 * initialization to provide a first seed to the secondary DRBG.
+	 */
+	if (lrng_pdrbg.pdrbg_min_seeded)
+		outbuflen = min_t(u32, outbuflen,
+				  lrng_pdrbg.pdrbg_entropy_bits>>3);
+	ret = lrng_drbg_generate_helper(drbg, outbuf, outbuflen);
+	if (ret != outbuflen) {
+		pr_warn(DRIVER_NAME": getting random data from primary DRBG failed (%d)\n",
+			ret);
+		return ret;
+	}
+	if (lrng_pdrbg.pdrbg_entropy_bits > (u32)(ret<<3))
+		lrng_pdrbg.pdrbg_entropy_bits -= ret<<3;
+	else
+		lrng_pdrbg.pdrbg_entropy_bits = 0;
+	dbg("obtained %d bytes of random data from primary DRBG\n", ret);
+	dbg("primary DRBG entropy level at %u bits\n",
+	    lrng_pdrbg.pdrbg_entropy_bits);
+	return ret;
+}
+
+/**
+ * Inject data into the primary DRBG with a given entropy value. The function
+ * calls the DRBG's update function. This function also generates random data
+ * if requested by caller. The caller is only returned the amount of random
+ * data that is at most equal to the amount of entropy that just seeded the
+ * DRBG.
+ *
+ * @inbuf buffer to inject
+ * @inbuflen length of inbuf
+ * @entropy_bits entropy value of the data in inbuf in bits
+ * @outbuf buffer to fill immediately after seeding to get full entropy
+ * @outbuflen length of outbuf
+ * @fullentropy start /dev/random output only after the DRBG was fully seeded
+ * @return number of bytes written to outbuf, 0 if outbuf is not supplied,
+ *	   or < 0 in case of error
+ */
+static int lrng_pdrbg_inject(const u8 *inbuf, u32 inbuflen, u32 entropy_bits,
+			     u8 *outbuf, u32 outbuflen, bool fullentropy)
+{
+	struct drbg_state *drbg = lrng_pdrbg.pdrbg;
+	int ret;
+	unsigned long flags;
+
+	/* cap the maximum entropy value to the provided data length */
+	entropy_bits = min_t(u32, entropy_bits, inbuflen<<3);
+
+	spin_lock_irqsave(&lrng_pdrbg_lock, flags);
+	ret = lrng_drbg_seed_helper(drbg, inbuf, inbuflen);
+	if (ret < 0) {
+		pr_warn(DRIVER_NAME": (re)seeding of primary DRBG failed\n");
+		goto unlock;
+	}
+	dbg("inject %u bytes with %u bits of entropy into primary DRBG\n",
+	    inbuflen, entropy_bits);
+	drbg->seeded = true;
+
+	/* Adjust the fill level indicator to at most the DRBG sec strength */
+	lrng_pdrbg.pdrbg_entropy_bits =
+		min_t(u32, lrng_pdrbg.pdrbg_entropy_bits + entropy_bits,
+		      LRNG_DRBG_SECURITY_STRENGTH_BITS);
+	lrng_pdrbg_init_ops(lrng_pdrbg.pdrbg_entropy_bits);
+
+	if (outbuf && outbuflen)
+		ret = lrng_pdrbg_generate(outbuf, outbuflen, fullentropy);
+
+unlock:
+	spin_unlock_irqrestore(&lrng_pdrbg_lock, flags);
+
+	if (lrng_have_entropy_full()) {
+		/* Wake readers */
+		wake_up_interruptible(&lrng_read_wait);
+		kill_fasync(&fasync, SIGIO, POLL_IN);
+	}
+
+	return ret;
+}
+
+/**
+ * Seed the DRBG from the internal noise sources.
+ */
+static int lrng_pdrbg_seed_internal(u8 *outbuf, u32 outbuflen, bool fullentropy)
+{
+	u8 entropy_buf[LRNG_DRBG_SECURITY_STRENGTH_BYTES +
+		       LRNG_IRQ_ENTROPY_BYTES];
+	u32 total_entropy_bits;
+	int ret;
+
+	/* No reseeding if sufficient entropy in primary DRBG */
+	if (lrng_pdrbg.pdrbg_entropy_bits >= outbuflen<<3) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&lrng_pdrbg_lock, flags);
+		ret = lrng_pdrbg_generate(outbuf, outbuflen, fullentropy);
+		spin_unlock_irqrestore(&lrng_pdrbg_lock, flags);
+		if (ret == outbuflen)
+			goto out;
+	}
+
+	/*
+	 * The pool should be large enough to allow fully seeding the DRBG with
+	 * its security strength if fast noise sources are not available.
+	 */
+	BUILD_BUG_ON(LRNG_POOL_SIZE_BYTES < LRNG_DRBG_SECURITY_STRENGTH_BYTES);
+	BUILD_BUG_ON(LRNG_DRBG_SECURITY_STRENGTH_BYTES % LRNG_POOL_WORD_BYTES);
+	/* entropy pool is read word-wise */
+	BUILD_BUG_ON(LRNG_IRQ_ENTROPY_BYTES % LRNG_POOL_WORD_BYTES);
+	BUILD_BUG_ON(LRNG_IRQ_ENTROPY_BYTES > LRNG_POOL_SIZE_BYTES);
+
+	/*
+	 * Concatenate the output of the noise sources. This would be the
+	 * spot to add an entropy extractor logic if desired. Note, this
+	 * entirety should have the ability to collect entropy equal or larger
+	 * than the DRBG strength to be able to feed /dev/random.
+	 */
+	total_entropy_bits = lrng_get_arch(entropy_buf);
+	/* drain the pool completely during init and when /dev/random calls */
+	total_entropy_bits += lrng_get_pool(
+			entropy_buf + LRNG_DRBG_SECURITY_STRENGTH_BYTES,
+			LRNG_IRQ_ENTROPY_BYTES,
+			LRNG_DRBG_SECURITY_STRENGTH_BITS - total_entropy_bits,
+			fullentropy || !lrng_pdrbg.pdrbg_fully_seeded);
+
+	dbg("reseed primary DRBG from internal noise sources with %u bits of entropy\n",
+	    total_entropy_bits);
+
+	ret = lrng_pdrbg_inject(entropy_buf, sizeof(entropy_buf),
+				total_entropy_bits,
+				outbuf, outbuflen, fullentropy);
+	memzero_explicit(entropy_buf, sizeof(entropy_buf));
+
+out:
+	/* Allow the seeding operation to be called again */
+	atomic_set(&lrng_pool.irq_info.reseed_in_progress, 0);
+
+	return ret;
+}
+
+/**
+ * Inject a data buffer into the secondary DRBG
+ *
+ * @inbuf buffer with data to inject
+ * @inbuflen buffer length
+ * @internal did random data originate from internal sources? Update the
+ *	     reseed threshold and the reseed timer when seeded with entropic
+ *	     data from noise sources to prevent unprivileged users from
+ *	     stopping reseeding the secondary DRBG with entropic data.
+ */
+static void lrng_sdrbg_inject(u8 *inbuf, u32 inbuflen, bool internal)
+{
+	unsigned long flags;
+
+	BUILD_BUG_ON(LRNG_DRBG_RESEED_THRESH > INT_MAX);
+	dbg("seeding secondary DRBG with %u bytes\n", inbuflen);
+	spin_lock_irqsave(&lrng_pdrbg_lock, flags);
+	if (lrng_drbg_seed_helper(lrng_sdrbg.sdrbg, inbuf, inbuflen) < 0) {
+		pr_warn(DRIVER_NAME": seeding of secondary DRBG failed\n");
+		atomic_set(&lrng_sdrbg.requests, 1);
+	} else if (internal) {
+		dbg("secondary DRBG stats since last seeding: %lu secs; generate calls: %d\n",
+		    (jiffies - lrng_sdrbg.last_seeded) / HZ,
+		    (LRNG_DRBG_RESEED_THRESH -
+		     atomic_read(&lrng_sdrbg.requests)));
+		lrng_sdrbg.last_seeded = jiffies;
+		atomic_set(&lrng_sdrbg.requests, LRNG_DRBG_RESEED_THRESH);
+	}
+	spin_unlock_irqrestore(&lrng_pdrbg_lock, flags);
+}
+
+/**
+ * Try to seed the secondary DRBG
+ *
+ * @seedfunc function to use to seed and obtain random data from primary DRBG
+ */
+static void lrng_sdrbg_seed(
+	int (*seed_func)(u8 *outbuf, u32 outbuflen, bool fullentropy))
+{
+	u8 seedbuf[LRNG_DRBG_SECURITY_STRENGTH_BYTES];
+	int ret;
+
+	dbg("reseed of secondary DRBG triggered\n");
+	ret = seed_func(seedbuf, LRNG_DRBG_SECURITY_STRENGTH_BYTES, false);
+	/* Update the DRBG state even though we received zero random data */
+	if (ret < 0) {
+		/*
+		 * Try to reseed at next round - note if EINPROGRESS is returned
+		 * the request counter may fall below zero in case of parallel
+		 * operations. We accept such "underflow" temporarily as the
+		 * counter will be set back to a positive number in the course
+		 * of the reseed. For these few generate operations under
+		 * heavy parallel strain of /dev/urandom we therefore exceed
+		 * the LRNG_DRBG_RESEED_THRESH threshold.
+		 */
+		if (ret != -EINPROGRESS)
+			atomic_set(&lrng_sdrbg.requests, 1);
+		return;
+	}
+
+	lrng_sdrbg_inject(seedbuf, ret, true);
+	memzero_explicit(seedbuf, ret);
+}
+
+/**
+ * DRBG reseed trigger: Kernel thread handler triggered by the schedule_work()
+ */
+static void lrng_pdrbg_seed_work(struct work_struct *dummy)
+{
+	dbg("reseed triggered by interrupt noise source\n");
+	lrng_sdrbg_seed(lrng_pdrbg_seed_internal);
+}
+
+/**
+ * DRBG reseed trigger: Synchronous reseed request
+ */
+static int lrng_pdrbg_seed(u8 *outbuf, u32 outbuflen, bool fullentropy)
+{
+	/* Ensure that the seeding only occurs once at any given time */
+	if (atomic_cmpxchg(&lrng_pool.irq_info.reseed_in_progress, 0, 1))
+		return -EINPROGRESS;
+	return lrng_pdrbg_seed_internal(outbuf, outbuflen, fullentropy);
+}
+
+/**
+ * Allocation of the DRBG state
+ */
+static struct drbg_state *lrng_drbg_alloc(void)
+{
+	struct drbg_state *drbg = NULL;
+	int coreref = -1;
+	bool pr = false;
+	int ret = 0;
+
+	drbg_convert_tfm_core(LRNG_DRBG_CORE, &coreref, &pr);
+	if (coreref < 0)
+		return NULL;
+
+	drbg = kzalloc(sizeof(struct drbg_state), GFP_KERNEL);
+	if (!drbg)
+		return NULL;
+
+	drbg->core = &drbg_cores[coreref];
+	drbg->seeded = false;
+	ret = drbg_alloc_state(drbg);
+	if (ret)
+		goto err;
+
+	ret = drbg->d_ops->crypto_init(drbg);
+	if (ret == 0)
+		return drbg;
+
+	drbg_dealloc_state(drbg);
+err:
+	kfree(drbg);
+	return NULL;
+}
+
+static int lrng_drbgs_alloc(void)
+{
+	unsigned long flags;
+	struct drbg_state *pdrbg, *sdrbg;
+
+	if (lrng_pdrbg.pdrbg && lrng_sdrbg.sdrbg)
+		return 0;
+
+	pdrbg = lrng_drbg_alloc();
+	if (!pdrbg)
+		return -EFAULT;
+	sdrbg = lrng_drbg_alloc();
+	if (!sdrbg) {
+		drbg_dealloc_state(pdrbg);
+		kfree(pdrbg);
+		return -EFAULT;
+	}
+
+	spin_lock_irqsave(&lrng_pdrbg_lock, flags);
+	if (lrng_pdrbg.pdrbg) {
+		drbg_dealloc_state(pdrbg);
+		kfree(pdrbg);
+	} else {
+		lrng_pdrbg.pdrbg = pdrbg;
+		INIT_WORK(&lrng_pdrbg.lrng_seed_work, lrng_pdrbg_seed_work);
+		pr_info(DRIVER_NAME": primary DRBG with %s core allocated\n",
+			lrng_pdrbg.pdrbg->core->backend_cra_name);
+	}
+	spin_unlock_irqrestore(&lrng_pdrbg_lock, flags);
+
+	spin_lock_irqsave(&lrng_sdrbg_lock, flags);
+	if (lrng_sdrbg.sdrbg) {
+		drbg_dealloc_state(sdrbg);
+		kfree(sdrbg);
+	} else {
+		lrng_sdrbg.sdrbg = sdrbg;
+		pr_info(DRIVER_NAME": secondary DRBG with %s core allocated\n",
+			lrng_sdrbg.sdrbg->core->backend_cra_name);
+	}
+	spin_unlock_irqrestore(&lrng_sdrbg_lock, flags);
+
+	return 0;
+}
+
+/**
+ * Obtain random data from DRBG with information theoretical entropy by
+ * triggering a reseed. The primary DRBG will only return as many random
+ * bytes as it was seeded with.
+ *
+ * @outbuf buffer to store the random data in
+ * @outbuflen length of outbuf
+ * @return: < 0 on error
+ *	    >= 0 the number of bytes that were obtained
+ */
+static int lrng_pdrbg_get(u8 *outbuf, u32 outbuflen)
+{
+	int ret;
+
+	if (!outbuf || !outbuflen)
+		return 0;
+
+	/* DRBG is not yet available */
+	if (!atomic_read(&lrng_pdrbg_avail))
+		return 0;
+
+	ret = lrng_pdrbg_seed(outbuf, outbuflen, true);
+	dbg("read %u bytes of full entropy data from primary DRBG\n", ret);
+
+	/* Shall we wake up user space writers? */
+	if (lrng_need_entropy()) {
+		wake_up_interruptible(&lrng_write_wait);
+		kill_fasync(&fasync, SIGIO, POLL_OUT);
+	}
+
+	return ret;
+}
+
+/**
+ * Initial RNG provides random data with as much entropy as we have
+ * at boot time until the DRBG becomes available during late_initcall() but
+ * before user space boots. When the DRBG is initialized, the initial RNG
+ * is retired.
+ *
+ * Note: until retirement of this RNG, the system did not generate too much
+ * entropy yet. Hence, a proven DRNG like a DRBG is not necessary here anyway.
+ *
+ * The RNG is using the following as noise source:
+ *	* high resolution time stamps
+ *	* the collected IRQ state
+ *	* CPU noise source if available
+ *
+ * Input/output: it is a drop-in replacement for lrng_sdrbg_get.
+ */
+static u32 lrng_init_state[SHA_WORKSPACE_WORDS];
+static int lrng_init_rng(u8 *outbuf, u32 outbuflen)
+{
+	u32 hash[SHA_DIGEST_WORDS];
+	u32 outbuflen_orig = outbuflen;
+	u32 workspace[SHA_WORKSPACE_WORDS];
+
+	BUILD_BUG_ON(sizeof(lrng_init_state[0]) != LRNG_POOL_WORD_BYTES);
+
+	sha_init(hash);
+	while (outbuflen) {
+		unsigned int arch;
+		u32 i;
+		u32 todo = min_t(u32, outbuflen,
+				 SHA_WORKSPACE_WORDS * sizeof(u32));
+
+		for (i = 0; i < SHA_WORKSPACE_WORDS; i++) {
+			if (arch_get_random_int(&arch))
+				lrng_init_state[i] ^= arch;
+			lrng_init_state[i] ^= random_get_entropy();
+			if (i < LRNG_POOL_SIZE)
+				lrng_init_state[i] ^=
+					atomic_read_u32(&lrng_pool.pool[i]);
+		}
+		sha_transform(hash, (u8 *)&lrng_init_state, workspace);
+		/* Mix generated data back in for backtracking resistance */
+		for (i = 0; i < SHA_DIGEST_WORDS; i++)
+			lrng_init_state[i] ^= hash[0];
+
+		memcpy(outbuf, hash, todo);
+		outbuf += todo;
+		outbuflen -= todo;
+		atomic_add(todo, &lrng_initrng_bytes);
+	}
+	memzero_explicit(hash, sizeof(hash));
+	memzero_explicit(workspace, sizeof(workspace));
+
+	return outbuflen_orig;
+}
+
+/**
+ * Get random data out of the secondary DRBG which is reseeded frequently. In
+ * the worst case, the DRBG may generate random numbers without being reseeded
+ * for LRNG_DRBG_RESEED_THRESH requests times LRNG_DRBG_MAX_REQSIZE bytes.
+ *
+ * If the DRBG is not yet initialized, use the initial RNG output.
+ *
+ * @outbuf buffer for storing random data
+ * @outbuflen length of outbuf
+ * @return < 0 in error case (DRBG geeneration or update failed)
+ *	   >=0 returning the returned number of bytes
+ */
+static int lrng_sdrbg_get(u8 *outbuf, u32 outbuflen)
+{
+	u32 processed = 0;
+	struct drbg_state *drbg = lrng_sdrbg.sdrbg;
+	unsigned long flags;
+	int ret;
+
+	if (!outbuf || !outbuflen)
+		return 0;
+
+	outbuflen = min_t(size_t, outbuflen, INT_MAX);
+
+	/* DRBG is not yet available */
+	if (!atomic_read(&lrng_pdrbg_avail)) {
+		spin_lock_irqsave(&lrng_init_rng_lock, flags);
+		/* Prevent race with lrng_init */
+		if (!atomic_read(&lrng_pdrbg_avail)) {
+			ret = lrng_init_rng(outbuf, outbuflen);
+			spin_unlock_irqrestore(&lrng_init_rng_lock, flags);
+			return ret;
+		}
+		spin_unlock_irqrestore(&lrng_init_rng_lock, flags);
+	}
+
+	while (outbuflen) {
+		unsigned long now = jiffies;
+		u32 todo = min_t(u32, outbuflen, LRNG_DRBG_MAX_REQSIZE);
+
+		if (atomic_dec_and_test(&lrng_sdrbg.requests) ||
+		    time_after(now, lrng_sdrbg.last_seeded +
+			       lrng_sdrbg_reseed_max_time * HZ))
+			lrng_sdrbg_seed(lrng_pdrbg_seed);
+
+		spin_lock_irqsave(&lrng_sdrbg_lock, flags);
+		ret = lrng_drbg_generate_helper(drbg, outbuf + processed, todo);
+		spin_unlock_irqrestore(&lrng_sdrbg_lock, flags);
+		if (ret <= 0) {
+			pr_warn(DRIVER_NAME": getting random data from secondary DRBG failed (%d)\n",
+				ret);
+			return -EFAULT;
+		}
+		processed += ret;
+		outbuflen -= ret;
+	}
+
+	return processed;
+}
+
+/************************** LRNG kernel interfaces ***************************/
+
+void get_random_bytes(void *buf, int nbytes)
+{
+	lrng_sdrbg_get((u8 *)buf, (u32)nbytes);
+}
+EXPORT_SYMBOL(get_random_bytes);
+
+/**
+ * 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
+ */
+void 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_sdrbg_get((u8 *)p, (u32)nbytes);
+}
+EXPORT_SYMBOL(get_random_bytes_arch);
+
+/**
+ * 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
+ *	   (re)seed the DRBG.
+ * @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)
+{
+	/* DRBG is not yet online */
+	if (!atomic_read(&lrng_pdrbg_avail))
+		return;
+	/*
+	 * 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,
+				 kthread_should_stop() || lrng_need_entropy());
+	lrng_pdrbg_inject(buffer, count, entropy_bits, NULL, 0, false);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
+
+/**
+ * Delete a previously registered readiness callback function.
+ */
+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 a callback function that will be invoked when the DRBG is fully seeded.
+ *
+ * returns: 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_pdrbg.pdrbg_fully_seeded))
+		return err;
+
+	owner = rdy->owner;
+	if (!try_module_get(owner))
+		return -ENOENT;
+
+	spin_lock_irqsave(&lrng_ready_list_lock, flags);
+	if (lrng_pdrbg.pdrbg_fully_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 user space interfaces *************************/
+
+static ssize_t lrng_read_common(char __user *buf, size_t nbytes,
+			int (*lrng_read_random)(u8 *outbuf, u32 outbuflen))
+{
+	ssize_t ret = 0;
+	u8 tmpbuf[LRNG_DRBG_BLOCKLEN_BYTES];
+	u8 *tmp_large = NULL;
+	u8 *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 (nbytes > LRNG_DRBG_BLOCKLEN_BYTES) {
+		tmplen = min_t(u32, nbytes, LRNG_DRBG_MAX_REQSIZE);
+		tmp_large = kmalloc(tmplen, GFP_KERNEL);
+		if (!tmp_large)
+			tmplen = sizeof(tmpbuf);
+		else
+			tmp = tmp_large;
+	}
+
+	while (nbytes) {
+		u32 todo = min_t(u32, nbytes, tmplen);
+		int rc = 0;
+
+		if (tmp_large && need_resched()) {
+			if (signal_pending(current)) {
+				if (ret == 0)
+					ret = -ERESTARTSYS;
+				break;
+			}
+			schedule();
+		}
+
+		rc = lrng_read_random(tmp, todo);
+		if (rc <= 0)
+			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_pdrbg_read_common(int nonblock, char __user *buf, size_t nbytes)
+{
+	ssize_t n;
+
+	if (nbytes == 0)
+		return 0;
+
+	nbytes = min_t(u32, nbytes, LRNG_DRBG_BLOCKLEN_BYTES);
+	while (1) {
+		n = lrng_read_common(buf, nbytes, lrng_pdrbg_get);
+		if (n < 0)
+			return n;
+		if (n > 0)
+			return n;
+
+		/* No entropy available.  Maybe wait and retry. */
+		if (nonblock)
+			return -EAGAIN;
+
+		wait_event_interruptible(lrng_read_wait,
+					 lrng_have_entropy_full());
+		if (signal_pending(current))
+			return -ERESTARTSYS;
+	}
+}
+
+static ssize_t lrng_pdrbg_read(struct file *file, char __user *buf,
+			       size_t nbytes, loff_t *ppos)
+{
+	return lrng_pdrbg_read_common(file->f_flags & O_NONBLOCK, buf, nbytes);
+}
+
+static unsigned int lrng_pdrbg_poll(struct file *file, poll_table *wait)
+{
+	unsigned int mask;
+
+	poll_wait(file, &lrng_read_wait, wait);
+	poll_wait(file, &lrng_write_wait, wait);
+	mask = 0;
+	if (lrng_have_entropy_full())
+		mask |= POLLIN | POLLRDNORM;
+	if (lrng_need_entropy())
+		mask |= POLLOUT | POLLWRNORM;
+	return mask;
+}
+
+static ssize_t lrng_drbg_write_common(const char __user *buffer, size_t count,
+				      u32 entropy_bits, bool sdrbg)
+{
+	ssize_t ret = 0;
+	u8 buf[64];
+	const char __user *p = buffer;
+
+	if (!atomic_read(&lrng_pdrbg_avail))
+		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 primary DRBG */
+		lrng_pdrbg_inject(buf, bytes, ent, NULL, 0, false);
+		/* Data from /dev/[|u]random is injected into secondary DRBG */
+		if (sdrbg)
+			lrng_sdrbg_inject(buf, bytes, false);
+
+		count -= bytes;
+		p += bytes;
+		ret += bytes;
+		entropy_bits -= ent;
+
+		cond_resched();
+	}
+
+	return ret;
+}
+
+static ssize_t lrng_sdrbg_read(struct file *file, char __user *buf,
+			       size_t nbytes, loff_t *ppos)
+{
+	return lrng_read_common(buf, nbytes, lrng_sdrbg_get);
+}
+
+static ssize_t lrng_drbg_write(struct file *file, const char __user *buffer,
+			       size_t count, loff_t *ppos)
+{
+	return lrng_drbg_write_common(buffer, count, 0, true);
+}
+
+static long lrng_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
+{
+	int size, ent_count;
+	int __user *p = (int __user *)arg;
+
+	switch (cmd) {
+	case RNDGETENTCNT:
+		ent_count = atomic_read(&lrng_pool.irq_info.num_events);
+		if (put_user(ent_count, p))
+			return -EFAULT;
+		return 0;
+	case RNDADDTOENTCNT:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		if (get_user(ent_count, p))
+			return -EFAULT;
+		if (ent_count < 0) {
+			/* ensure that entropy count cannot go below zero */
+			ent_count = -ent_count;
+			ent_count = min(ent_count,
+				atomic_read(&lrng_pool.irq_info.num_events));
+			atomic_sub(ent_count, &lrng_pool.irq_info.num_events);
+		} else {
+			ent_count = min_t(int, ent_count, LRNG_POOL_SIZE_BITS);
+			atomic_add(ent_count, &lrng_pool.irq_info.num_events);
+		}
+		return 0;
+	case RNDADDENTROPY:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		if (get_user(ent_count, p++))
+			return -EFAULT;
+		if (ent_count < 0)
+			return -EINVAL;
+		if (get_user(size, p++))
+			return -EFAULT;
+		if (size < 0)
+			return -EINVAL;
+		/* there cannot be more entropy than data */
+		ent_count = min(ent_count, size);
+		/* ent_count is in bytes, but lrng_drbg_write requires bits */
+		return lrng_drbg_write_common((const char __user *)p, size,
+					      ent_count<<3, false);
+	case RNDZAPENTCNT:
+	case RNDCLEARPOOL:
+		/* Clear the entropy pool counter. */
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		atomic_set(&lrng_pool.irq_info.num_events, 0);
+		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_pdrbg_read,
+	.write = lrng_drbg_write,
+	.poll  = lrng_pdrbg_poll,
+	.unlocked_ioctl = lrng_ioctl,
+	.fasync = lrng_fasync,
+	.llseek = noop_llseek,
+};
+
+const struct file_operations urandom_fops = {
+	.read  = lrng_sdrbg_read,
+	.write = lrng_drbg_write,
+	.unlocked_ioctl = lrng_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))
+		return -EINVAL;
+
+	if (count > INT_MAX)
+		count = INT_MAX;
+
+	if (flags & GRND_RANDOM)
+		return lrng_pdrbg_read_common(flags & GRND_NONBLOCK, buf,
+					      count);
+
+	if (unlikely(!lrng_pdrbg.pdrbg_fully_seeded)) {
+		if (flags & GRND_NONBLOCK)
+			return -EAGAIN;
+		wait_event_interruptible(lrng_pdrbg_init_wait,
+					 lrng_pdrbg.pdrbg_fully_seeded);
+		if (signal_pending(current))
+			return -ERESTARTSYS;
+	}
+	return lrng_sdrbg_read(NULL, buf, count, NULL);
+}
+
+/*************************** LRNG proc interfaces ****************************/
+
+#ifdef CONFIG_SYSCTL
+
+#include <linux/sysctl.h>
+
+static int lrng_min_read_thresh = LRNG_POOL_WORD_BITS;
+static int lrng_min_write_thresh;
+static int lrng_max_read_thresh = LRNG_POOL_SIZE_BITS;
+static int lrng_max_write_thresh = LRNG_POOL_SIZE_BITS;
+static char lrng_sysctl_bootid[16];
+static int lrng_sdrbg_reseed_max_min;
+
+/*
+ * This function is used to return both the bootid UUID, and random
+ * UUID.  The difference is in whether table->data is NULL; if it is,
+ * then a new UUID is generated and returned to the user.
+ *
+ * If the user accesses this via the proc interface, the UUID will be
+ * returned as an ASCII string in the standard UUID format; if via the
+ * sysctl system call, as 16 bytes of binary data.
+ */
+static int lrng_proc_do_uuid(struct ctl_table *table, int write,
+			     void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table fake_table;
+	unsigned char buf[64], tmp_uuid[16], *uuid;
+
+	uuid = table->data;
+	if (!uuid) {
+		uuid = tmp_uuid;
+		generate_random_uuid(uuid);
+	} else {
+		static DEFINE_SPINLOCK(bootid_spinlock);
+
+		spin_lock(&bootid_spinlock);
+		if (!uuid[8])
+			generate_random_uuid(uuid);
+		spin_unlock(&bootid_spinlock);
+	}
+
+	sprintf(buf, "%pU", uuid);
+
+	fake_table.data = buf;
+	fake_table.maxlen = sizeof(buf);
+
+	return proc_dostring(&fake_table, write, buffer, lenp, ppos);
+}
+
+static int lrng_proc_do_type(struct ctl_table *table, int write,
+			     void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table fake_table;
+	unsigned char buf[30];
+
+	snprintf(buf, sizeof(buf), "%s: %s",
+#ifdef CONFIG_CRYPTO_DRBG_HMAC
+		 "HMAC DRBG",
+#elif defined CONFIG_CRYPTO_DRBG_CTR
+		 "CTR DRBG",
+#elif defined CONFIG_CRYPTO_DRBG_HASH
+		 "HASH DRBG",
+#else
+		 "unknown",
+#endif
+		 lrng_pdrbg.pdrbg->core->backend_cra_name);
+
+	fake_table.data = buf;
+	fake_table.maxlen = sizeof(buf);
+
+	return proc_dostring(&fake_table, write, buffer, lenp, ppos);
+}
+
+/* Return entropy available scaled to integral bits */
+static int lrng_proc_do_entropy(struct ctl_table *table, int write,
+				void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table fake_table;
+	int entropy_count;
+
+	entropy_count = atomic_read((atomic_t *)table->data);
+	if (table->extra2)
+		entropy_count = min_t(int, entropy_count,
+				      *(int *)table->extra2);
+
+	fake_table.data = &entropy_count;
+	fake_table.maxlen = sizeof(entropy_count);
+
+	return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
+}
+
+static int lrng_proc_drbg_seed(struct ctl_table *table, int write,
+			       void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table fake_table;
+	int drbg_seeded = 0;
+	bool *seeded = (bool *)table->data;
+
+	if (*seeded)
+		drbg_seeded = 1;
+
+	fake_table.data = &drbg_seeded;
+	fake_table.maxlen = sizeof(drbg_seeded);
+
+	return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
+}
+
+static int lrng_sysctl_poolsize = LRNG_POOL_SIZE_BITS;
+static int pdrbg_security_strength = LRNG_DRBG_SECURITY_STRENGTH_BYTES;
+extern struct ctl_table random_table[];
+struct ctl_table random_table[] = {
+	{
+		.procname	= "poolsize",
+		.data		= &lrng_sysctl_poolsize,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.procname	= "entropy_avail",
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_do_entropy,
+		.data		= &lrng_pool.irq_info.num_events,
+		.extra2		= &lrng_max_write_thresh,
+	},
+	{
+		.procname	= "read_wakeup_threshold",
+		.data		= &lrng_read_wakeup_bits,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &lrng_min_read_thresh,
+		.extra2		= &lrng_max_read_thresh,
+	},
+	{
+		.procname	= "write_wakeup_threshold",
+		.data		= &lrng_write_wakeup_bits,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &lrng_min_write_thresh,
+		.extra2		= &lrng_max_write_thresh,
+	},
+	{
+		.procname	= "boot_id",
+		.data		= &lrng_sysctl_bootid,
+		.maxlen		= 16,
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_do_uuid,
+	},
+	{
+		.procname	= "uuid",
+		.maxlen		= 16,
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_do_uuid,
+	},
+	{
+		.procname       = "urandom_min_reseed_secs",
+		.data           = &lrng_sdrbg_reseed_max_time,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+		.extra1		= &lrng_sdrbg_reseed_max_min,
+	},
+	{
+		.procname	= "drbg_fully_seeded",
+		.data		= &lrng_pdrbg.pdrbg_fully_seeded,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_drbg_seed,
+	},
+	{
+		.procname	= "drbg_minimally_seeded",
+		.data		= &lrng_pdrbg.pdrbg_min_seeded,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_drbg_seed,
+	},
+	{
+		.procname	= "drbg_type",
+		.maxlen		= 30,
+		.mode		= 0444,
+		.proc_handler	= lrng_proc_do_type,
+	},
+	{
+		.procname	= "drbg_security_strength",
+		.data		= &pdrbg_security_strength,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= proc_dointvec,
+	},
+	{ }
+};
+#endif /* CONFIG_SYSCTL */
+
+/***************************** Initialize DRBG *******************************/
+
+static int __init lrng_init(void)
+{
+	unsigned long flags;
+
+	BUG_ON(lrng_drbgs_alloc());
+	BUG_ON(LRNG_DRBG_BLOCKLEN_BYTES !=
+	       lrng_pdrbg.pdrbg->core->blocklen_bytes);
+	BUG_ON(LRNG_DRBG_SECURITY_STRENGTH_BYTES !=
+	       drbg_sec_strength(lrng_pdrbg.pdrbg->core->flags));
+
+	/* This RNG does not work if no high-resolution timer is available */
+	BUG_ON(!random_get_entropy() && !random_get_entropy());
+
+	/*
+	 * As we use the IRQ entropic input data processed by the init RNG
+	 * again during lrng_pdrbg_seed_internal, we must not claim that
+	 * the init RNG state has any entropy when injecting its contents as
+	 * an initial seed into the DRBG.
+	 */
+	spin_lock_irqsave(&lrng_init_rng_lock, flags);
+	lrng_pdrbg_inject((u8 *)&lrng_init_state,
+			  SHA_WORKSPACE_WORDS * sizeof(lrng_init_state[0]),
+			  0, NULL, 0, false);
+	lrng_sdrbg_seed(lrng_pdrbg_seed);
+	atomic_inc(&lrng_pdrbg_avail);
+	memzero_explicit(&lrng_init_state,
+			 SHA_WORKSPACE_WORDS * sizeof(lrng_init_state[0]));
+	spin_unlock_irqrestore(&lrng_init_rng_lock, flags);
+	pr_info(DRIVER_NAME": deactivating initial RNG - %d bytes delivered",
+		atomic_read(&lrng_initrng_bytes));
+	return 0;
+}
+
+/* A late init implies that more interrupts are collected for initial seeding */
+late_initcall(lrng_init);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Stephan Mueller <smueller@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Linux Random Number Generator");
-- 
2.5.5