Messages in this thread | | | Date | Wed, 28 Aug 2019 17:20:41 +0200 | From | David Sterba <> | Subject | Re: [GIT pull] x86/urgent for 5.3-rc5 |
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On Tue, Aug 27, 2019 at 07:39:55PM +0200, Borislav Petkov wrote: > @@ -42,5 +43,24 @@ void x86_init_rdrand(struct cpuinfo_x86 *c) > return; > } > } > + > + /* > + * Stupid sanity-check whether RDRAND does *actually* generate > + * some at least random-looking data. > + */ > + prev = tmp; > + for (i = 0; i < SANITY_CHECK_LOOPS; i++) { > + if (rdrand_long(&tmp)) { > + if (prev != tmp) > + changed++;
You could do some sort of weak statistical test like
if (popcnt(prev ^ tmp) < BITS_PER_LONG / 3) bad++;
if (bad > TOO_BAD) WARN(...);
this should catch same value, increments you mentioned and possibly other trivial classes of not-so-random values.
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