The test interface allows a privileged process to capture the raw
unconditioned noise that is collected by the Jitter RNG for statistical
analysis. Such testing allows the analysis how much entropy
the Jitter RNG noise source provides on a given platform. The obtained
data is the time stamp sampled by the Jitter RNG. Considering that
the Jitter RNG inserts the delta of this time stamp compared to the
immediately preceding time stamp, the obtained data needs to be
post-processed accordingly to obtain the data the Jitter RNG inserts
into its entropy pool.
The raw entropy collection is provided to obtain the raw unmodified
time stamps that are about to be added to the Jitter RNG entropy pool
and are credited with entropy. Thus, this patch adds an interface
which renders the Jitter RNG insecure. This patch is NOT INTENDED
FOR PRODUCTION SYSTEMS, but solely for development/test systems to
verify the available entropy rate.
Access to the data is given through the jent_raw_hires debugfs file.
The data buffer should be multiples of sizeof(u32) to fill the entire
buffer. Using the option jitterentropy_testing.boot_raw_hires_test=1
the raw noise of the first 1000 entropy events since boot can be
sampled.
This test interface allows generating the data required for
analysis whether the Jitter RNG is in compliance with SP800-90B
sections 3.1.3 and 3.1.4.
If the test interface is not compiled, its code is a noop which has no
impact on the performance.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Using the kernel crypto API, the SHA3-256 algorithm is used as
conditioning element to replace the LFSR in the Jitter RNG. All other
parts of the Jitter RNG are unchanged.
The application and use of the SHA-3 conditioning operation is identical
to the user space Jitter RNG 3.4.0 by applying the following concept:
- the Jitter RNG initializes a SHA-3 state which acts as the "entropy
pool" when the Jitter RNG is allocated.
- When a new time delta is obtained, it is inserted into the "entropy
pool" with a SHA-3 update operation. Note, this operation in most of
the cases is a simple memcpy() onto the SHA-3 stack.
- To cause a true SHA-3 operation for each time delta operation, a
second SHA-3 operation is performed hashing Jitter RNG status
information. The final message digest is also inserted into the
"entropy pool" with a SHA-3 update operation. Yet, this data is not
considered to provide any entropy, but it shall stir the entropy pool.
- To generate a random number, a SHA-3 final operation is performed to
calculate a message digest followed by an immediate SHA-3 init to
re-initialize the "entropy pool". The obtained message digest is one
block of the Jitter RNG that is returned to the caller.
Mathematically speaking, the random number generated by the Jitter RNG
is:
aux_t = SHA-3(Jitter RNG state data)
Jitter RNG block = SHA-3(time_i || aux_i || time_(i-1) || aux_(i-1) ||
... || time_(i-255) || aux_(i-255))
when assuming that the OSR = 1, i.e. the default value.
This operation implies that the Jitter RNG has an output-blocksize of
256 bits instead of the 64 bits of the LFSR-based Jitter RNG that is
replaced with this patch.
The patch also replaces the varying number of invocations of the
conditioning function with one fixed number of invocations. The use
of the conditioning function consistent with the userspace Jitter RNG
library version 3.4.0.
The code is tested with a system that exhibited the least amount of
entropy generated by the Jitter RNG: the SiFive Unmatched RISC-V
system. The measured entropy rate is well above the heuristically
implied entropy value of 1 bit of entropy per time delta. On all other
tested systems, the measured entropy rate is even higher by orders
of magnitude. The measurement was performed using updated tooling
provided with the user space Jitter RNG library test framework.
The performance of the Jitter RNG with this patch is about en par
with the performance of the Jitter RNG without the patch.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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>
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>
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>
