[PATCH v4 0/5] /dev/random - a new approach

From: Stephan Mueller
Date: Tue May 31 2016 - 14:42:54 EST

Hi Herbert, Ted,

The following patch set provides a different approach to /dev/random which
I call Linux Random Number Generator (LRNG) to collect entropy within the Linux
kernel. The main improvements compared to the legacy /dev/random is to provide
sufficient entropy during boot time as well as in virtual environments and when
using SSDs. A secondary design goal is to limit the impact of the entropy
collection on massive parallel systems and also allow the use accelerated
cryptographic primitives. Also, all steps of the entropic data processing are
testable. Finally massive performance improvements are visible at /dev/urandom
and get_random_bytes.

The design and implementation is driven by a set of goals described in [1]
that the LRNG completely implements. Furthermore, [1] includes a
comparison with RNG design suggestions such as SP800-90B, SP800-90C, and

Changes v4:
* port to 4.7-rc1
* Use classical twisted LFSR approach to collect entropic data as requested by
George Spelvin. The LFSR is based on a primitive and irreducible polynomial
whose taps are not too close to the location the current byte is mixed in.
Primitive polynomials for other entropy pool sizes are offered in the code.
* The reading of the entropy pool is performed with a hash. The hash can be
specified at compile time. The pre-defined hashes are the same as used for
the DRBG type (e.g. a SHA256 Hash DRBG implies the use of SHA-256, an AES256
CTR DRBG implies the use of CMAC-AES).
* Addition of the example defines for a CTR DRBG with AES128 which can be
enabled during compile time.
* Entropy estimate: one bit of entropy per interrupt. In case a system does
not have a high-resolution timer, apply 1/10th bit of entropy per interrupt.
The interrupt estimates can be changed arbitrarily at compile time.
* Use kmalloc_node for the per-NUMA node secondary DRBGs.
* Add boot time entropy tests discussed in section 3.4.3 [1].
* Align all buffers that are processed by the kernel crypto API to an 8 byte
boundary. This boundary covers all currently existing cipher implementations.

Changes v3:
* Convert debug printk to pr_debug as suggested by Joe Perches
* Add missing \n as suggested by Joe Perches
* Do not mix in struck IRQ measurements as requested by Pavel Machek
* Add handling logic for systems without high-res timer as suggested by Pavel
Machek -- it uses ideas from the add_interrupt_randomness of the legacy
/dev/random implementation
* add per NUMA node secondary DRBGs as suggested by Andi Kleen -- the
explanation of how the logic works is given in section 2.1.1 of my
documentation [1], especially how the initial seeding is performed.

Changes v2:
* Removal of the Jitter RNG fast noise source as requested by Ted
* Addition of processing of add_input_randomness as suggested by Ted
* Update documentation and testing in [1] to cover the updates
* Addition of a SystemTap script to test add_input_randomness
* To clarify the question whether sufficient entropy is present during boot
I added one more test in 3.3.1 [1] which demonstrates the providing of
sufficient entropy during initialization. In the worst case of no fast noise
sources, in the worst case of a virtual machine with only very few hardware
devices, the testing shows that the secondary DRBG is fully seeded with 256
bits of entropy before user space injects the random data obtained
during shutdown of the previous boot (i.e. the requirement phrased by the
legacy /dev/random implementation). As the writing of the random data into
/dev/random by user space will happen before any cryptographic service
is initialized in user space, this test demonstrates that sufficient
entropy is already present in the LRNG at the time user space requires it
for seeding cryptographic daemons. Note, this test result was obtained
for different architectures, such as x86 64 bit, x86 32 bit, ARM 32 bit and
MIPS 32 bit.

[1] http://www.chronox.de/lrng/doc/lrng.pdf

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

Stephan Mueller (5):
crypto: DRBG - externalize DRBG functions for LRNG
random: conditionally compile code depending on LRNG
crypto: Linux Random Number Generator
crypto: LRNG - enable compile
random: add interrupt callback to VMBus IRQ handler

crypto/Kconfig | 10 +
crypto/Makefile | 1 +
crypto/drbg.c | 11 +-
crypto/lrng.c | 1981 ++++++++++++++++++++++++++++++++++++++++++++++++
drivers/char/random.c | 9 +
drivers/hv/vmbus_drv.c | 3 +
include/crypto/drbg.h | 7 +
include/linux/genhd.h | 5 +
include/linux/random.h | 7 +-
9 files changed, 2027 insertions(+), 7 deletions(-)
create mode 100644 crypto/lrng.c