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2023-05-24crypto: jitter - permanent and intermittent health errorsStephan Müller
[ Upstream commit 3fde2fe99aa6dacd4151c87382b07ce7f30f0a52 ] According to SP800-90B, two health failures are allowed: the intermittend and the permanent failure. So far, only the intermittent failure was implemented. The permanent failure was achieved by resetting the entire entropy source including its health test state and waiting for two or more back-to-back health errors. This approach is appropriate for RCT, but not for APT as APT has a non-linear cutoff value. Thus, this patch implements 2 cutoff values for both RCT/APT. This implies that the health state is left untouched when an intermittent failure occurs. The noise source is reset and a new APT powerup-self test is performed. Yet, whith the unchanged health test state, the counting of failures continues until a permanent failure is reached. Any non-failing raw entropy value causes the health tests to reset. The intermittent error has an unchanged significance level of 2^-30. The permanent error has a significance level of 2^-60. Considering that this level also indicates a false-positive rate (see SP800-90B section 4.2) a false-positive must only be incurred with a low probability when considering a fleet of Linux kernels as a whole. Hitting the permanent error may cause a panic(), the following calculation applies: Assuming that a fleet of 10^9 Linux kernels run concurrently with this patch in FIPS mode and on each kernel 2 health tests are performed every minute for one year, the chances of a false positive is about 1:1000 based on the binomial distribution. In addition, any power-up health test errors triggered with jent_entropy_init are treated as permanent errors. A permanent failure causes the entire entropy source to permanently return an error. This implies that a caller can only remedy the situation by re-allocating a new instance of the Jitter RNG. In a subsequent patch, a transparent re-allocation will be provided which also changes the implied heuristic entropy assessment. In addition, when the kernel is booted with fips=1, the Jitter RNG is defined to be part of a FIPS module. The permanent error of the Jitter RNG is translated as a FIPS module error. In this case, the entire FIPS module must cease operation. This is implemented in the kernel by invoking panic(). The patch also fixes an off-by-one in the RCT cutoff value which is now set to 30 instead of 31. This is because the counting of the values starts with 0. Reviewed-by: Vladis Dronov <vdronov@redhat.com> Signed-off-by: Stephan Mueller <smueller@chronox.de> Reviewed-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-12-11crypto: jitter - don't limit ->health_failure check to FIPS modeNicolai Stange
The jitterentropy's Repetition Count Test (RCT) as well as the Adaptive Proportion Test (APT) are run unconditionally on any collected samples. However, their result, i.e. ->health_failure, will only get checked if fips_enabled is set, c.f. the jent_health_failure() wrapper. I would argue that a RCT or APT failure indicates that something's seriously off and that this should always be reported as an error, independently of whether FIPS mode is enabled or not: it should be up to callers whether or not and how to handle jitterentropy failures. Make jent_health_failure() to unconditionally return ->health_failure, independent of whether fips_enabled is set. Note that fips_enabled isn't accessed from the jitterentropy code anymore now. Remove the linux/fips.h include as well as the jent_fips_enabled() wrapper. Signed-off-by: Nicolai Stange <nstange@suse.de> Reviewed-by: Stephan Mueller <smueller@chronox.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-10-18crypto: jitter - add header to fix buildwarningsBen Dooks
Fix the following build warnings by adding a header for the definitions shared between jitterentropy.c and jitterentropy-kcapi.c. Fixes the following: crypto/jitterentropy.c:445:5: warning: symbol 'jent_read_entropy' was not declared. Should it be static? crypto/jitterentropy.c:475:18: warning: symbol 'jent_entropy_collector_alloc' was not declared. Should it be static? crypto/jitterentropy.c:509:6: warning: symbol 'jent_entropy_collector_free' was not declared. Should it be static? crypto/jitterentropy.c:516:5: warning: symbol 'jent_entropy_init' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:59:6: warning: symbol 'jent_zalloc' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:64:6: warning: symbol 'jent_zfree' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:69:5: warning: symbol 'jent_fips_enabled' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:74:6: warning: symbol 'jent_panic' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:79:6: warning: symbol 'jent_memcpy' was not declared. Should it be static? crypto/jitterentropy-kcapi.c:93:6: warning: symbol 'jent_get_nstime' was not declared. Should it be static? Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> Reviewed-by: Stephan Mueller <smueller@chronox.de Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>