Re: [edk2-devel] [PATCH v2 07/13] SecurityPkg: RngDxe: Remove incorrect limitation on GetRng

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 9 May 2024 at 07:56, Doug Flick via groups.io
<dougflick=microsoft.com@groups.io> wrote:
>
> Removed from gEfiRngAlgorithmRaw an incorrect assumption that
> Raw cannot return less than 256 bits. The DRNG Algorithms
> should always use a 256 bit seed as per nist standards
> however a caller is free to request less than 256 bits.
> >
> >     //
> >    // When a DRBG is used on the output of a entropy source,
> >    // its security level must be at least 256 bits according to UEFI Spec.
> >    //
> >    if (RNGValueLength < 32) {
> >      return EFI_INVALID_PARAMETER;
> >    }
> >
>
> AARCH64 platforms do not have this limitation and this brings both
> implementations into alignment with each other and the spec.
>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
>
> Signed-off-by: Doug Flick [MSFT] <doug.edk2@gmail.com>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

As I commented in the other thread, it is not the job of the raw
EFI_RNG_PROTOCOL to ensure that its callers never do anything silly.
Refusing requests for less than 32 bytes is pointless and arbitrary,
as only avoids one very particular potential mistake.


> ---
>  SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c | 8 --------
>  1 file changed, 8 deletions(-)
>
> diff --git a/SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c b/SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c
> index 7e06e16e4be5..5723ed695747 100644
> --- a/SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c
> +++ b/SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c
> @@ -116,14 +116,6 @@ RngGetRNG (
>    // The "raw" algorithm is intended to provide entropy directly
>    //
>    if (CompareGuid (RNGAlgorithm, &gEfiRngAlgorithmRaw)) {
> -    //
> -    // When a DRBG is used on the output of a entropy source,
> -    // its security level must be at least 256 bits according to UEFI Spec.
> -    //
> -    if (RNGValueLength < 32) {
> -      return EFI_INVALID_PARAMETER;
> -    }
> -
>      Status = GenerateEntropy (RNGValueLength, RNGValue);
>      return Status;
>    }
> --
> 2.34.1
>
>
>
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