LRNG - add power-on and runtime self-tests

Parts of the LFSR are already covered by self-tests, including:

* Self-test of SP800-90A DRBG provided by the Linux kernel crypto API.

* Self-test of the PRNG provided by the Linux kernel crypto API.

* Raw noise source data testing including SP800-90B compliant
  tests when enabling CONFIG_LRNG_HEALTH_TESTS

This patch adds the self tests for the remaining critical functions of
the LRNG that are essential to maintain entropy and provide
cryptographic strong random numbers. The following self tests are
implemented:

* Self-test of the time array maintenance. This test verifies whether
the time stamp array management to store multiple values in one integer
implements a concatenation of the data.

* Self-test of the LFSR operation. This test injects a monotonic
increasing counter into the LFSR. After completion of the injection of
the counter, 3 pool words are compared with known good values. The known
good values are calculated with the newly-developed tool
lfsr_testvector_generation provided as part of the LRNG test tool set at
[1].

* Self-test of the Hash_DF operation ensures that this function operates
compliant to the specification. The self-test performs a Hash_DF
operation of a zeroized entropy pool state. The test vectors are
generated using the newly-developed tool hash_df_testvector_generation
provided as part of the LRNG test tool set at [1].

* Self-test of the ChaCha20 DRNG is based on the self tests that are
already present and implemented with the stand-alone user space
ChaCha20 DRNG implementation available at [2]. The self-tests cover
different use cases of the DRNG seeded with known seed data.

The status of the LRNG self-tests is provided with the selftest_status
SysFS file. If the file contains a zero, the self-tests passed. The
value 0xffffffff means that the self-tests were not executed. Any other
value indicates a self test failure.

The self-test may be compiled to panic the system if the self-test
fails.

All self tests operate on private state data structures. This implies
that none of the self-tests have any impact on the regular LRNG
operations. This allows the self-tests to be repeated at runtime by
writing anything into the selftest_status SysFS file.

[1] https://www.chronox.de/lrng.html
[2] https://www.chronox.de/chacha20.html

CC: "Eric W. Biederman" <ebiederm@xmission.com>
CC: "Alexander E. Patrakov" <patrakov@gmail.com>
CC: "Ahmed S. Darwish" <darwish.07@gmail.com>
CC: "Theodore Y. Ts'o" <tytso@mit.edu>
CC: Willy Tarreau <w@1wt.eu>
CC: Matthew Garrett <mjg59@srcf.ucam.org>
CC: Vito Caputo <vcaputo@pengaru.com>
CC: Andreas Dilger <adilger.kernel@dilger.ca>
CC: Jan Kara <jack@suse.cz>
CC: Ray Strode <rstrode@redhat.com>
CC: William Jon McCann <mccann@jhu.edu>
CC: zhangjs <zachary@baishancloud.com>
CC: Andy Lutomirski <luto@kernel.org>
CC: Florian Weimer <fweimer@redhat.com>
CC: Lennart Poettering <mzxreary@0pointer.de>
CC: Nicolai Stange <nstange@suse.de>
CC: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
CC: Neil Horman <nhorman@redhat.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>

drivers/char/lrng/Kconfig

@@ -175,4 +175,29 @@ config LRNG_TESTING
 
 	  If unsure, say N.
 
+config LRNG_SELFTEST
+	bool "Enable power-on and on-demand self-tests"
+	help
+	  The power-on self tests are executed during boot time
+	  covering the ChaCha20 DRNG, the LFSR processing and the
+	  time stamp management of the LRNG.
+
+	  The on-demand self-tests are triggered by writing any
+	  value into the SysFS file selftest_status. At the same
+	  time, when reading this file, the test status is
+	  returned. A zero indicates that all tests were executed
+	  successfully.
+
+	  If unsure, say Y.
+
+if LRNG_SELFTEST
+
+config LRNG_SELFTEST_PANIC
+	bool "Panic the kernel upon self-test failure"
+	help
+	  If the option is enabled, the kernel is terminated if an
+	  LRNG power-on self-test failure is detected.
+
+endif # LRNG_SELFTEST
+
 endif # LRNG

drivers/char/lrng/Makefile

@@ -16,3 +16,4 @@ obj-$(CONFIG_LRNG_KCAPI)	+= lrng_kcapi.o
 obj-$(CONFIG_LRNG_JENT)		+= lrng_jent.o
 obj-$(CONFIG_LRNG_HEALTH_TESTS)	+= lrng_health.o
 obj-$(CONFIG_LRNG_TESTING)	+= lrng_testing.o
+obj-$(CONFIG_LRNG_SELFTEST)	+= lrng_selftest.o