The Jitter RNG time delta is computed based on the difference of two
high-resolution, 64-bit time stamps. However, the test interface added
in 69f1c387ba only outputs the lower 32 bits of those time stamps. To
ensure all information is available during the evaluation process of
the Jitter RNG, output the full 64-bit time stamps.
Any clients collecting data from the test interface will need to be
updated to take this change into account.
Additionally, the size of the temporary buffer that holds the data for
user space has been clarified. Previously, this buffer was
JENT_TEST_RINGBUFFER_SIZE (= 1000) bytes in size, however that value
represents the number of samples held in the kernel space ring buffer,
with each sample taking 8 (previously 4) bytes.
Rather than increasing the size to allow for all 1000 samples to be
output, we keep it at 1000 bytes, but clarify that this means at most
125 64-bit samples will be output every time this interface is called.
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Joachim Vandersmissen <git@jvdsn.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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>
