linux-kernel - [RFC][PATCH 0/6] /dev/random

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Date:	Thu, 21 Apr 2016 11:11:55 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Ted Tso <tytso@....edu>, herbert@...dor.apana.org.au
Cc:	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	sandyinchina@...il.com
Subject: [RFC][PATCH 0/6] /dev/random - a new approach

Hi Herbert, Ted,

The venerable Linux /dev/random served users of cryptographic mechanisms well
for a long time. Its behavior is well understood to deliver entropic data. In
the last years, however, the Linux /dev/random showed signs of age where it has
challenges to cope with modern computing environments ranging from tiny embedded
systems, over new hardware resources such as SSDs, up to massive parallel
systems as well as virtualized environments.

With the experience gained during numerous studies of /dev/random, entropy
assessments of different noise source designs and assessing entropy behavior in
virtual machines and other special environments, I felt to do something about
it.

I developed a different approach, 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 / 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
AIS20/31.

Please find in [1] the full design discussion covering qualitative assessments
of the entropy collection and entropy flow. Furthermore, a full testing of the
data collection and data processing is performed. The testing focuses on the
calculation of different types of minimum entropy values of raw noise data.
All used test code and supportive tools are provided with [2]. The testing
is concluded with a comparison to the legacy /dev/random implementation
regarding performance and delivery time of entropic random data.

To support a proper review of the code without interfering with the current
functionality, the attached patch adds the LRNG to the cryptodev-2.6 tree as
an option. The patches do not replace or even alter the legacy /dev/random
implementation but allows the user to enable the LRNG at compile time. If it is
enabled, the legacy /dev/random implementation is not compiled. On the other
hand, if the LRNG support is disabled, the legacy /dev/random code is
compiled unchanged. With this approach you see that the LRNG is API and ABI
compatible with the legacy implementation.

Stability tests were executed on 64 and 32 bit systems where the test KVM with 4
vCPUs on 4 hyperthreads compiled the Linux kernel with make -j4 over and over
for half a day. In addition, parallel cat /dev/urandom > /dev/null were
exercised for a couple of hours. Also, stability tests by generating 500
million interrupts were performed.

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

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

Stephan Mueller (6):
  crypto: DRBG - externalize DRBG functions for LRNG
  random: conditionally compile code depending on LRNG
  crypto: Linux Random Number Generator
  crypto: LRNG - enable compile
  crypto: LRNG - hook LRNG into interrupt handler
  hyperv IRQ handler: trigger LRNG

 crypto/Kconfig         |   10 +
 crypto/Makefile        |    1 +
 crypto/drbg.c          |   11 +-
 crypto/lrng.c          | 1803 ++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/char/random.c  |    8 +
 drivers/hv/vmbus_drv.c |    3 +
 include/crypto/drbg.h  |    7 +
 include/linux/genhd.h  |    5 +
 include/linux/random.h |    8 +
 kernel/irq/handle.c    |    1 +
 10 files changed, 1851 insertions(+), 6 deletions(-)
 create mode 100644 crypto/lrng.c

-- 
2.5.5

,

Ciao
Stephan