[edk2-devel] [PATCH 2/3] MdePkg: Refactor BaseRngLib to support AARCH64 in addition to X86
Rebecca Cran
rebecca at nuviainc.com
Wed May 5 19:27:54 UTC 2021
On 5/4/21 3:09 PM, Sami Mujawar wrote:
>> +EFIAPI
>> +BaseRngLibConstructor (
>> + VOID
>> + )
>> +{
>> + UINT64 Isar0;
>> + //
>> + // Determine RNDR support by examining bits 63:60 of the ISAR0 register returned by
>> + // MSR. A non-zero value indicates that the processor supports the RNDR instruction.
>> + //
>> + Isar0 = ArmReadIdIsar0 ();
>> + ASSERT ((Isar0 & RNDR_MASK) != 0);
>> + (void)Isar0;
> [SAMI] ASSERTs will vanish in the release builds. So, I think this needs
> to be an if condition. If RNDR is not supported RETURN_UNSUPPORTED
> should be returned.
> However, it appears thatthe auto generated function
> ProcessLibraryConstructorList() disregards the error code returned by
> the constructor (see Build\...\AutoGen.c files). So it looks like the
> loading operation would continue in release builds despite of an error.
> I am not aware if this is the desired behavior or why the status code
> returned by the constructor is disregarded.
>
> However, this would be a probem in the current case as subsequent calls
> to generate random numbers will result in an undefined instruction
> exception.
> To prevent this, I think the above check should be done in either
> - ArmRndr()/ArmRndrrs()
> or
> - preferably in ArchGetRandomNumberXX(), which should return an
> error code EFI_UNSUPPORTED, EFI_NOT_READY or EFI_SUCCESS. However, the
> impact on IA32/x64 code needs to be evaluated.
>
> [/SAMI]
Yes, I noticed that but the same problem exists for the IA32/x64 code,
since it might not support RDRAND/RDSEED. Should I change the BaseRngLib
interface to return an EFI_STATUS instead of BOOLEAN? Or would that be
too disruptive?
--
Rebecca Cran
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