• Stephan Müller's avatar
    crypto: jitter - consider 32 LSB for APT · 552d03a2
    Stephan Müller authored
    The APT compares the current time stamp with a pre-set value. The
    current code only considered the 4 LSB only. Yet, after reviews by
    mathematicians of the user space Jitter RNG version >= 3.1.0, it was
    concluded that the APT can be calculated on the 32 LSB of the time
    delta. Thi change is applied to the kernel.
    
    This fixes a bug where an AMD EPYC fails this test as its RDTSC value
    contains zeros in the LSB. The most appropriate fix would have been to
    apply a GCD calculation and divide the time stamp by the GCD. Yet, this
    is a significant code change that will be considered for a future
    update. Note, tests showed that constantly the GCD always was 32 on
    these systems, i.e. the 5 LSB were always zero (thus failing the APT
    since it only considered the 4 LSB for its calculation).
    Signed-off-by: default avatarStephan Mueller <smueller@chronox.de>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    552d03a2
jitterentropy.c 25.1 KB