Re: [edk2-devel] [PATCH v2 1/1] MdePkg/BaseRngLib: Add a smoketest for RDRAND and check CPUID

["Michael D Kinney" <michael.d.kinney@intel.com>]

[-- Attachment #1: Type: text/plain, Size: 2049 bytes --]

Hi Pedro,

Pointers to external content that were used to create the code
change can be captured in the BZ and the commit message.

Thanks,

Mike

From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Pedro Falcato
Sent: Tuesday, November 22, 2022 7:56 AM
To: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: devel@edk2.groups.io; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <gaoliming@byosoft.com.cn>; Liu, Zhiguang <zhiguang.liu@intel.com>
Subject: Re: [edk2-devel] [PATCH v2 1/1] MdePkg/BaseRngLib: Add a smoketest for RDRAND and check CPUID

On Tue, Nov 22, 2022 at 3:39 PM Jason A. Donenfeld <Jason@zx2c4.com<mailto:Jason@zx2c4.com>> wrote:
On Tue, Nov 22, 2022 at 4:32 PM Pedro Falcato <pedro.falcato@gmail.com<mailto: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


[-- Attachment #2: Type: text/html, Size: 42804 bytes --]