Re: [edk2-devel] [PATCH v1 07/14] NetworkPkg:: SECURITY PATCH CVE-2023-45237

["Doug Flick via groups.io" <dougflick=microsoft.com@groups.io>]

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Ard,

I went ahead an added your suggestion to use gEfiRngAlgorithmRaw. This however led me to discover a difference in behavior in x86 based platforms and Arm based platforms and I'm usure which is the correct behavior.

On x86 based platforms, if the RngValueLength being requested is less than 32 (256bits). Then it returns EFI_INVALID_PARAMETER (despite the function header not indicating that's possible)
https://github.com/tianocore/edk2/blob/b82c9631da39ca5a1f0702185a46fea60446dd0a/SecurityPkg/RandomNumberGenerator/RngDxe/Rand/RngDxe.c#L123

and it assumes that "When a Deterministic Random Bit Generator (DRBG) is used on the output of a (raw) entropy source, its security level must be at least 256 bits." means it shouldn't support requests smaller than 32 bytes.
https://uefi.org/specs/UEFI/2.10/37_Secure_Technologies.html#random-number-generator-protocol 

On Arm based Platforms it doesn't make this assumption and behaves according to the specification.
https://github.com/tianocore/edk2/blob/b82c9631da39ca5a1f0702185a46fea60446dd0a/SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c#L106C35-L106C54

Right now my thought is that x86 machines are making an incorrect assumption where the seed to a DRNG needs to be at least 256 bits by nist recommendations but a caller should be free to request values smaller than 32 bytes.

Would you assume the same before I make a change to the x86 code to remove that check?


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