Re: [PATCH] UefiCpuPkg/Microcode: Fix incorrect checksum issue for extended table

["Ni, Ray" <ray.ni@intel.com>]

I agree with Chao's comments.
Please add more code comments to:
1. describe the uCode format
2. explain all the 3 code blocks that checks the checksum.

> -----Original Message-----
> From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of Zhang,
> Chao B
> Sent: Tuesday, February 19, 2019 9:06 AM
> To: Chen, Chen A <chen.a.chen@intel.com>; edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>
> Subject: Re: [edk2] [PATCH] UefiCpuPkg/Microcode: Fix incorrect checksum
> issue for extended table
> 
> Chen Chen:
>    I think you can add uCode format info into comments. Also please highlight
> in comment Which part is header checksum calculation, which part is for
> extended header
> 
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Chen A Chen
> Sent: Monday, February 18, 2019 1:54 PM
> To: edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>
> Subject: [edk2] [PATCH] UefiCpuPkg/Microcode: Fix incorrect checksum
> issue for extended table
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1020
> 
> The following Microcode payload format is define in SDM spec.
> Payload:
> |MicrocodeHeader|MicrocodeBinary|ExtendedHeader|ExtendedTable|.
> When we verify the CheckSum32 with ExtendedTable, we should use the
> fields of ExtendedTable to replace corresponding fields in MicrocodeHeader,
> and then calculate the CheckSum32 with MicrocodeHeader+MicrocodeBinary.
> This patch already verified on ICL platform.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Chen A Chen <chen.a.chen@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/Microcode.c | 38
> ++++++++++++++++++++++++--------
>  1 file changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/Microcode.c
> b/UefiCpuPkg/Library/MpInitLib/Microcode.c
> index d84344c6f5..38880cdbec 100644
> --- a/UefiCpuPkg/Library/MpInitLib/Microcode.c
> +++ b/UefiCpuPkg/Library/MpInitLib/Microcode.c
> @@ -57,6 +57,7 @@ MicrocodeDetect (
>    UINT32                                  LatestRevision;
>    UINTN                                   TotalSize;
>    UINT32                                  CheckSum32;
> +  UINT32                                  InCompleteCheckSum32;
>    BOOLEAN                                 CorrectMicrocode;
>    VOID                                    *MicrocodeData;
>    MSR_IA32_PLATFORM_ID_REGISTER           PlatformIdMsr;
> @@ -121,6 +122,26 @@ MicrocodeDetect (
>    MicrocodeData  = NULL;
>    MicrocodeEnd = (UINTN) (CpuMpData->MicrocodePatchAddress +
> CpuMpData->MicrocodePatchRegionSize);
>    MicrocodeEntryPoint = (CPU_MICROCODE_HEADER *) (UINTN)
> CpuMpData->MicrocodePatchAddress;
> +
> +  //
> +  // To avoid double calculate checksum32 value.
> +  // Save the CheckSum32 of the common parts in advance.
> +  //
> +  if (MicrocodeEntryPoint->DataSize == 0) {
> +    InCompleteCheckSum32 = CalculateSum32 (
> +                             (UINT32 *) MicrocodeEntryPoint,
> +                             sizeof (CPU_MICROCODE_HEADER) + 2000
> +                             );
> +  } else {
> +    InCompleteCheckSum32 = CalculateSum32 (
> +                             (UINT32 *) MicrocodeEntryPoint,
> +                             sizeof (CPU_MICROCODE_HEADER) + MicrocodeEntryPoint-
> >DataSize
> +                             );
> +  }
> +  InCompleteCheckSum32 -=
> + MicrocodeEntryPoint->ProcessorSignature.Uint32;
> +  InCompleteCheckSum32 -= MicrocodeEntryPoint->ProcessorFlags;
> +  InCompleteCheckSum32 -= MicrocodeEntryPoint->Checksum;
> +
>    do {
>      //
>      // Check if the microcode is for the Cpu and the version is newer @@ -
> 137,14 +158,10 @@ MicrocodeDetect (
>            MicrocodeEntryPoint->UpdateRevision > LatestRevision &&
>            (MicrocodeEntryPoint->ProcessorFlags & (1 << PlatformId))
>            ) {
> -        if (MicrocodeEntryPoint->DataSize == 0) {
> -          CheckSum32 = CalculateSum32 ((UINT32 *) MicrocodeEntryPoint, 2048);
> -        } else {
> -          CheckSum32 = CalculateSum32 (
> -                         (UINT32 *) MicrocodeEntryPoint,
> -                         MicrocodeEntryPoint->DataSize + sizeof
> (CPU_MICROCODE_HEADER)
> -                         );
> -        }
> +        CheckSum32 = InCompleteCheckSum32;
> +        CheckSum32 += MicrocodeEntryPoint->ProcessorSignature.Uint32;
> +        CheckSum32 += MicrocodeEntryPoint->ProcessorFlags;
> +        CheckSum32 += MicrocodeEntryPoint->Checksum;
>          if (CheckSum32 == 0) {
>            CorrectMicrocode = TRUE;
>            ProcessorFlags = MicrocodeEntryPoint->ProcessorFlags;
> @@ -171,7 +188,10 @@ MicrocodeDetect (
>                ExtendedTableCount = ExtendedTableHeader-
> >ExtendedSignatureCount;
>                ExtendedTable      = (CPU_MICROCODE_EXTENDED_TABLE *)
> (ExtendedTableHeader + 1);
>                for (Index = 0; Index < ExtendedTableCount; Index ++) {
> -                CheckSum32 = CalculateSum32 ((UINT32 *) ExtendedTable,
> sizeof(CPU_MICROCODE_EXTENDED_TABLE));
> +                CheckSum32 = InCompleteCheckSum32;
> +                CheckSum32 += ExtendedTable->ProcessorSignature.Uint32;
> +                CheckSum32 += ExtendedTable->ProcessorFlag;
> +                CheckSum32 += ExtendedTable->Checksum;
>                  if (CheckSum32 == 0) {
>                    //
>                    // Verify Header
> --
> 2.16.2.windows.1
> 
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