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Date:   Sat, 27 Feb 2021 14:33:40 +0100
From:   Stephan Müller <>
To:     Tso Ted <>,
Cc:     Willy Tarreau <>, Nicolai Stange <>,
        LKML <>,
        Arnd Bergmann <>,
        Greg Kroah-Hartman <>,
        "Eric W. Biederman" <>,
        "Alexander E. Patrakov" <>,
        "Ahmed S. Darwish" <>,
        Matthew Garrett <>,
        Vito Caputo <>,
        Andreas Dilger <>,
        Jan Kara <>, Ray Strode <>,
        William Jon McCann <>,
        zhangjs <>,
        Andy Lutomirski <>,
        Florian Weimer <>,
        Lennart Poettering <>,
        Peter Matthias <>,
        Marcelo Henrique Cerri <>,
        Neil Horman <>,
        Randy Dunlap <>,
        Julia Lawall <>,
        Dan Carpenter <>,
        Andy Lavr <>,
        Eric Biggers <>,
        "Jason A. Donenfeld" <>,
        Petr Tesarik <>,
        John Haxby <>
Subject: [PATCH v38 00/13] /dev/random - a new approach


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. It provides the same API and ABI and can be used as a
drop-in replacement.

The LRNG implements at least all features of the existing /dev/random such as
NUMA-node-local DRNGs. Patches 1 through 3 provide the code that is feature-
identical. The following advantages compared to the existing /dev/random
implementation are present:

* Sole use of crypto for data processing:

 - Exclusive use of a hash operation for conditioning entropy data with
   a clear mathematical description as given in [2] section 2.2 -
   non-cryptographic operations like LFSR are not used.

 - The LRNG uses only properly defined and implemented cryptographic
   algorithms unlike the use of the SHA-1 transformation in the existing
   /dev/random implementation.

 - Hash operations use NUMA-node-local hash instances to benefit large
   parallel systems.

 - LRNG uses limited number of data post-processing steps as documented in
   [2] section 2.2 compared to the large variation of different
   post-processing steps in the existing /dev/random implementation that
   have no apparent mathematical description (see [2] section 4.5).

* Performance

 - Faster by up to 130% in the critical code path of the interrupt handler
   depending on data collection size configurable at kernel compile time -
   the default is now set such that the highest performance is achieved as
   outlined in [2] section 4.2.

 - Configurable data collection sizes to accommodate small environments
   and big environments via CONFIG_LRNG_COLLECTION_SIZE.

 - Entropy collection using an almost never contended lock to benefit
   large parallel systems – worst case rate of contention is the number
   of DRNG reseeds, usually the number of potential contentions per 10
   minutes is equal to number of NUMA nodes.

 - ChaCha20 DRNG is significantly faster as implemented in the existing
   /dev/random as demonstrated with [2] table 2.

 - Faster entropy collection during boot time to reach fully seeded
   level, including on virtual systems or systems with SSDs as outlined
   in [2] section 4.1.

* Testing

 - Availability of run-time health tests of the raw unconditioned
   noise source to identify degradation of the available entropy as
   documented in [2] section 2.5.4. Such health tests are important
   today due to virtual machine monitors reducing the resolution of
   or disabling the high-resolution timer.

 - Heuristic entropy estimation is based on quantitative measurements
   and analysis following SP800-90B and not on coincidental
   underestimation of entropy applied by the existing /dev/random as
   outlined in [4] section 4.4.

 - Power-on self tests for critical deterministic components (ChaCha20
   DRNG, software hash implementation, and entropy collection logic)
   not already covered by power-up tests of the kernel crypto API as
   documented in [2] section 2.14.

 - Availability of test interfaces for all operational stages of the
   LRNG including boot-time raw entropy event data sampling as outlined
   in [2] section 2.15.

 - Fully testable ChaCha20 DRNG via a userspace ChaCha20 DRNG
   implementation [3].

 - In case of using the kernel crypto API SHASH hash implementation, it
   is fully testable and tested via the NIST ACVP test framework, for
   example certificates A734, A737, and A738.

 - The LRNG offers a test interface to validate the used software hash
   implementation and in particular that the LRNG invokes the hash
   correctly, allowing a NIST ACVP-compliant test cycle - see [2]
   section 2.15.

 - Availability of stress testing covering the different code paths for
   data and mechanism (de)allocations and code paths covered with locks.

* Entropy collection

 - The LRNG is shipped with test tools allowing the collection of
   raw unconditioned entropy during runtime and boot time available at

 - Full entropy assessment and description is provided with [2] chapter 3,
   specifically section 3.2.6.

 - Guarantee that entropy events are not credited with entropy twice
   (the existing /dev/random implementation credits HID/disk and
   interrupt events with entropy which are a derivative of each other).

* Configurable

 - LRNG kernel configuration allows configuration that is functionally
   equivalent to the existing /dev/random. Non-compiled additional code
   is folded into no-ops.

 - The following additional functions are compile-time selectable
   independent of each other:

  + Enabling of switchable cryptographic implementation support. This
    allows enabling an SP800-90A DRBG.

  + Enabling of using Jitter RNG noise source.

  + Enabling of noise source health tests.

  + Enabling of test interface allowing to enable each test interface

  + Enabling of the power-up self test.

 - At boot-time, the SP800-90B health tests can be enabled as outlined
   in [2] section 2.5.4.

 - At boot-time, the entropy rate used to credit the external CPU-based
   noise source and Jitter RNG noise source can be configured including
   setting an entropy rate of zero or full entropy - see [2] sections
   2.5.2 and 2.5.3.

* Run-time pluggable cryptographic implementations used for all data
  processing steps specified in [2] section 2.2

 - The DRNG can be replaced with a different implementation allowing
   any type of DRNG to provide data via the output interfaces. The LRNG
   provides the following types of DRNG implementations:

  + ChaCha20-based software implementation that is used per default.

  + SP800-90A DRBG using accelerated cryptographic implementations that
    may sleep.

  + Any DRNG that is accessible via the kernel crypto API RNG subsystem.

 - The hash component can be replaced with any other hash implementation
   provided the implementation does not sleep. The LRNG provides the
   access to the following types of non-sleeping hash implementations:

  + SHA-256 software implementation that is used per default. Due to
    kernel build system inconsistencies, the software SHA-1 implementation
    is used if the kernel crypto API is not compiled.

  + SHA-512 hash using the fastest hash implementation available via the
    kernel crypto API SHASH subsystem.

* Code structure

 - The LRNG source code is available for current upstream Linux kernel
   separate to the existing /dev/random which means that users who are
   conservative can use the unchanged existing /dev/random implementation.

 - Back-port patches are available at [5] to apply the LRNG to Linux
   kernel versions of 5.8, 5.4, 4.19, 4.14, 4.12, and 4.10. Patches for
   other kernel versions are easily derived from the existing ones.

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".

An entropy analysis is performed on the following systems - details
are given in [2] appendix C:

* x86 KVM virtualized guest 32 and 64 bit systems

* x86 bare metal

* older and newer ARMv7 system

* ARM64


* IBM Z System mainframe

* old MIPS embedded device

* testing with GCC and Clang

[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) - individual patches
are visible at

- Use new SHA header files

- simplify code initializing ChaCha20

- simplify code processing time stamp

- Simplify code for self test

- use u32 instead of uint32_t

- increase entropy pool size config values

- report available pool size

- add hash update operation to add yet uncompressed entropy data in
  data array into entropy pool during DRNG seeding

- Support disabling of continuous compression - this allows a user to
  disable the continuous hash compression operation performed in
  interrupt context once the per-CPU data array is full. In this case,
  the continuous compression operation is disabled, the compression is
  performed when the DRNG is reseeded. This implies that no hash operation
  is performed in interrupt context at all and thus increases the performance
  even further. Yet, the drawback is that entropy data may be overwritten
  instead of compressed.

CC: Torsten Duwe <>
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 <>
CC: Eric Biggers <>
Tested-by: Roman Drahtmüller <>
Tested-by: Marcelo Henrique Cerri <>

Stephan Mueller (13):
  Linux Random Number Generator
  LRNG - allocate one DRNG instance per NUMA node
  LRNG - sysctls and /proc interface
  LRNG - add switchable DRNG support
  LRNG - add common generic hash 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

 MAINTAINERS                                   |   7 +
 crypto/drbg.c                                 |  16 +-
 crypto/jitterentropy-kcapi.c                  |   3 +-
 crypto/jitterentropy.c                        |  31 +-
 drivers/char/Kconfig                          |   2 +
 drivers/char/Makefile                         |   9 +-
 drivers/char/lrng/Kconfig                     | 403 ++++++++++
 drivers/char/lrng/Makefile                    |  20 +
 drivers/char/lrng/lrng_archrandom.c           |  93 +++
 drivers/char/lrng/lrng_aux.c                  | 136 ++++
 drivers/char/lrng/lrng_chacha20.c             | 347 +++++++++
 drivers/char/lrng/lrng_chacha20.h             |  29 +
 drivers/char/lrng/lrng_drbg.c                 | 197 +++++
 drivers/char/lrng/lrng_drng.c                 | 406 +++++++++++
 drivers/char/lrng/lrng_health.c               | 407 +++++++++++
 drivers/char/lrng/lrng_interfaces.c           | 649 +++++++++++++++++
 drivers/char/lrng/lrng_internal.h             | 429 +++++++++++
 drivers/char/lrng/lrng_jent.c                 |  88 +++
 drivers/char/lrng/lrng_kcapi.c                | 225 ++++++
 drivers/char/lrng/lrng_kcapi_hash.c           |  97 +++
 drivers/char/lrng/lrng_kcapi_hash.h           |  19 +
 drivers/char/lrng/lrng_numa.c                 | 120 +++
 drivers/char/lrng/lrng_pool.c                 | 449 ++++++++++++
 drivers/char/lrng/lrng_proc.c                 | 184 +++++
 drivers/char/lrng/lrng_selftest.c             | 351 +++++++++
 drivers/char/lrng/lrng_sw_noise.c             | 669 +++++++++++++++++
 drivers/char/lrng/lrng_sw_noise.h             |  71 ++
 drivers/char/lrng/lrng_switch.c               | 207 ++++++
 drivers/char/lrng/lrng_testing.c              | 689 ++++++++++++++++++
 include/crypto/drbg.h                         |   7 +
 .../crypto/internal}/jitterentropy.h          |   3 +
 include/linux/lrng.h                          |  79 ++
 32 files changed, 6432 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_kcapi_hash.c
 create mode 100644 drivers/char/lrng/lrng_kcapi_hash.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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