Re: [PATCH v2 1/1] MdePkg/BaseRngLib: Add a smoketest for RDRAND and check CPUID

["Pedro Falcato" <pedro.falcato@gmail.com>]

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On Tue, Nov 22, 2022 at 3:39 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:

> On Tue, Nov 22, 2022 at 4:32 PM Pedro Falcato <pedro.falcato@gmail.com>
> wrote:
> > +  // Testing algorithm inspired by linux's
> arch/x86/kernel/cpu/rdrand.c:x86_init_rdrand
> > +  // as relicensed by the author, Jason Donenfeld, in the EDK2 mailing
> list.
> > +  // As is, the algorithm samples rdrand $RDRAND_TEST_SAMPLES times and
> expects
> > +  // a different result $RDRAND_MIN_CHANGE times for reliable RDRAND
> usage.
>
> You don't need to pepper my name all over the source. :)
>

I just wanted to properly credit you :) If you're not okay with it I can
remove it in a v3.

> +  for (TestIteration = 0; TestIteration < RDRAND_TEST_SAMPLES;
> TestIteration++) {
> > +    UINT32  Sample;
> > +    //
> > +    // Note: We use a retry loop for rdrand. Normal users get this in
> BaseRng.c
> > +    // Any failure to get a random number will assume RDRAND does not
> work.
> > +    //
> > +    for (Idx = 0; Idx < RDRAND_RETRIES; Idx++) {
> > +      if (AsmRdRand32 (&Sample)) {
>
> The linux code will use a 64bit value on 64bit machines. I suggest you
> do the same here -- use native word size. I think EFI calls this a
> "UINTN".
>

Hmm, do you reckon it makes a difference? I'm not intimately familiar with
HWRNG internals. Unfortunately there's no AsmRdRandUintn
so this would take some per-bitness #define's which... yeah, I'd rather not.

Pedro

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