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Subject[PATCH v28 00/12] /dev/random - a new approach with full SP800-90B

The following patch set provides a different approach to /dev/random which is
called Linux Random Number Generator (LRNG) to collect entropy within the Linux
kernel. The main improvements compared to the existing /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

The LRNG patch set allows a user to select use of the existing /dev/random or
the LRNG during compile time. As the LRNG provides API and ABI compatible
interfaces to the existing /dev/random implementation, the user can freely chose
the RNG implementation without affecting kernel or user space operations.

This patch set provides early boot-time entropy which implies that no
additional flags to the getrandom(2) system call discussed recently on
the LKML is considered to be necessary. Yet, if additional flags are
introduced to cover special hardware, the LRNG implementation will also
provide them to be fully ABI and API compliant as already discussed on

The LRNG is fully compliant to SP800-90B requirements and is shipped with a
full SP800-90B assessment and all required test tools. The existing /dev/random
implementation on the other hand has architectural limitations which
does not easily allow to bring the implementation in compliance with
SP800-90B. The key statement that causes concern is SP800-90B section
3.1.6. This section denies crediting entropy to multiple similar noise
sources. This section explicitly references different noise sources resting
on the timing of events and their derivatives (i.e. it is a direct complaint
to the existing existing /dev/random implementation). Therefore, SP800-90B
now denies the very issue mentioned in [1] with the existing /dev/random
implementation for a long time: crediting entropy to interrupts as well as
crediting entropy to derivatives of interrupts (HID and disk events). This is
not permissible with SP800-90B.

SP800-90B specifies various requirements for the noise source(s) that seed any
DRNG including SP800-90A DRBGs. In about a year from now, SP800-90B will be
mandated for all noise sources that provide entropy to DRBGs as part of a FIPS
140-[2|3] validation or other evaluation types. That means, if we there are no
solutions to comply with the requirements of SP800-90B found till one year
from now, any random number generation and ciphers based on random numbers
on Linux will be considered and treated as not applicable and delivering
no entropy! As /dev/urandom, getrandom(2) and /dev/random are the most
common and prevalent noise sources for DRNGs, all these DRNGs are affected.
This applies across the board for all validations of cryptography executing on
Linux (kernel and user space modules).

For users that are not interested in SP800-90B, the entire code for the
compliance as well as test interfaces can be deselected at compile time.

The design and implementation is driven by a set of goals described in [1]
that the LRNG completely implements. Furthermore, [1] includes the full
assessment of the SP800-90B compliance as well as a comparison with RNG
design suggestions of SP800-90C, and AIS20/31.

The LRNG provides a complete separation of the noise source maintenance
and the collection of entropy into an entropy pool from the post-processing
using a pseudo-random number generator. Different DRNGs are supported,

* The LRNG can be compile-time enabled to replace the existing /dev/random
implementation. When not selecting the LRNG at compile time (default), the
existing /dev/random implementation is built.

* Built-in ChaCha20 DRNG which has no dependency to other kernel

* SP800-90A DRBG using the kernel crypto API including its accelerated
raw cipher implementations. This implies that the output of /dev/random,
getrandom(2), /dev/urandom or get_random_bytes is fully compliant to

* Arbitrary DRNGs registered with the kernel crypto API

* Full compliance with SP800-90B which covers the startup and runtime health
tests mandated by SP800-90B as well as providing the test tools and test
interfaces to obtain raw noise data securely. The test tools are provided at

Booting the patch with the kernel command line option
"dyndbg=file drivers/char/lrng/* +p" generates logs indicating the operation
of the LRNG. Each log is pre-pended with "lrng".

The LRNG has a flexible design by allowing an easy replacement of the
deterministic random number generator component.

Compared to the existing /dev/random implementation, the compiled binary
is smaller when the LRNG is compiled with all options equal to the
existing /dev/random (i.e. only CONFIG_LRNG is set): random.o is 52.5 kBytes
whereas all LRNG object files are in 49 kBytes in size. The fully
SP800-90A/SP800-90B compliant binary code (CONFIG_LRNG,
uses some 61 kBytes. In addition, the LRNG is about 50% faster in the
performance critical interrupt handler code path compared to the existing
/dev/random implementation.

[1] - If the patch is accepted, I would
be volunteering to convert the documentation into RST format and
contribute it to the Linux kernel documentation directory.

Changes (compared to the previous patch set):

* make comments compliant to kernel-doc style

* update LRNG_RCT_CUTOFF from 30 to 31 (a cutoff of 30 implies
an alpha of 2^-29 and a cutoff of 31 is an alpha of 2^-30 - both
values are in line with SP800-90B, but to be consistent with documentation
update the cutoff value) - reported by Marcos Portnoi

* remove lrng_drng_generate_helper_full that was only needed by removed
TRNG support

* Remove "unlikely" from lrng_drng_lock which seems to cause additional grief
with sparse. Note, sparse will still report a lock context imbalance as it
used to since we indeed have two lock contexts as documented in
lrng_drng_switch. Reported-by: kbuild test robot <>

* Fix allocation size calculation in self-test code as reported by
Dan Carpenter <>

This patch requires the presence of patch
75551dbf112c992bc6c99a972990b3f272247e23 from Ted Tso's kernel tree
(specifically the addition of GRND_INSECURE to random.h)

As a side node: With the switchable DRNG support offered in this patch set,
the following areas could be removed. As the existing /dev/random has no support
for switchable DRNGs, however, this is not yet feasible though.

* remove lrng_ready_list and all code around it in lrng_interfaces.c

* remove the kernel crypto API RNG API to avoid having two random number
providing APIs - this would imply that all RNGs developed for this API would
be converted to the LRNG interface

CC: "Eric W. Biederman" <>
CC: "Alexander E. Patrakov" <>
CC: "Ahmed S. Darwish" <>
CC: "Theodore Y. Ts'o" <>
CC: Willy Tarreau <>
CC: Matthew Garrett <>
CC: Vito Caputo <>
CC: Andreas Dilger <>
CC: Jan Kara <>
CC: Ray Strode <>
CC: William Jon McCann <>
CC: zhangjs <>
CC: Andy Lutomirski <>
CC: Florian Weimer <>
CC: Lennart Poettering <>
CC: Nicolai Stange <>
Tested-by: Roman Drahtmüller <>
Tested-by: Marcelo Henrique Cerri <>

Stephan Mueller (12):
Linux Random Number Generator
LRNG - allocate one DRNG instance per NUMA node
LRNG - sysctls and /proc interface
LRNG - add switchable DRNG support
crypto: DRBG - externalize DRBG functions for LRNG
LRNG - add SP800-90A DRBG extension
LRNG - add kernel crypto API PRNG extension
crypto: provide access to a static Jitter RNG state
LRNG - add Jitter RNG fast noise source
LRNG - add SP800-90B compliant health tests
LRNG - add interface for gathering of raw entropy
LRNG - add power-on and runtime self-tests

crypto/drbg.c | 16 +-
crypto/jitterentropy-kcapi.c | 3 +-
crypto/jitterentropy.c | 25 +-
drivers/char/Kconfig | 2 +
drivers/char/Makefile | 9 +-
drivers/char/lrng/Kconfig | 203 ++++++
drivers/char/lrng/Makefile | 19 +
drivers/char/lrng/lrng_archrandom.c | 94 +++
drivers/char/lrng/lrng_aux.c | 148 ++++
drivers/char/lrng/lrng_chacha20.c | 265 ++++++++
drivers/char/lrng/lrng_chacha20.h | 25 +
drivers/char/lrng/lrng_drbg.c | 260 +++++++
drivers/char/lrng/lrng_drng.c | 400 +++++++++++
drivers/char/lrng/lrng_health.c | 409 +++++++++++
drivers/char/lrng/lrng_interfaces.c | 637 ++++++++++++++++++
drivers/char/lrng/lrng_internal.h | 305 +++++++++
drivers/char/lrng/lrng_jent.c | 89 +++
drivers/char/lrng/lrng_kcapi.c | 327 +++++++++
drivers/char/lrng/lrng_lfsr.h | 152 +++++
drivers/char/lrng/lrng_numa.c | 101 +++
drivers/char/lrng/lrng_pool.c | 588 ++++++++++++++++
drivers/char/lrng/lrng_proc.c | 163 +++++
drivers/char/lrng/lrng_selftest.c | 418 ++++++++++++
drivers/char/lrng/lrng_sw_noise.c | 102 +++
drivers/char/lrng/lrng_sw_noise.h | 57 ++
drivers/char/lrng/lrng_switch.c | 183 +++++
drivers/char/lrng/lrng_testing.c | 271 ++++++++
include/crypto/drbg.h | 7 +
.../crypto/internal}/jitterentropy.h | 3 +
include/linux/lrng.h | 63 ++
31 files changed, 5341 insertions(+), 10 deletions(-)
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_drbg.c
create mode 100644 drivers/char/lrng/lrng_drng.c
create mode 100644 drivers/char/lrng/lrng_health.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_jent.c
create mode 100644 drivers/char/lrng/lrng_kcapi.c
create mode 100644 drivers/char/lrng/lrng_lfsr.h
create mode 100644 drivers/char/lrng/lrng_numa.c
create mode 100644 drivers/char/lrng/lrng_pool.c
create mode 100644 drivers/char/lrng/lrng_proc.c
create mode 100644 drivers/char/lrng/lrng_selftest.c
create mode 100644 drivers/char/lrng/lrng_sw_noise.c
create mode 100644 drivers/char/lrng/lrng_sw_noise.h
create mode 100644 drivers/char/lrng/lrng_switch.c
create mode 100644 drivers/char/lrng/lrng_testing.c
rename {crypto => include/crypto/internal}/jitterentropy.h (84%)
create mode 100644 include/linux/lrng.h


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