Re: [PATCH V2] UefiCpuPkg/MpInitLib: MicrocodeDetect: Ensure checked range is valid

["Dong, Eric" <eric.dong@intel.com>]

Hi Zhichao,

Reviewed-by: Eric Dong <eric.dong@intel.com>

It's better to add some comments in the code to explain the change which make the code easy to be understood.

Thanks,
Eric

> -----Original Message-----
> From: Gao, Zhichao
> Sent: Tuesday, June 25, 2019 11:16 PM
> To: devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Laszlo
> Ersek <lersek@redhat.com>; Gao, Liming <liming.gao@intel.com>
> Subject: [PATCH V2] UefiCpuPkg/MpInitLib: MicrocodeDetect: Ensure
> checked range is valid
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1934
> 
> V1:
> Originally, the checksum part would done before verfiy the microcode data.
> Which meas the checksum would be done for a meaningless data.
> It would cause a incorrect TotalSize (the size of microcode data), then
> incorrect checksum and incorrect pointer increasing would happen.
> To fix this, move the checksum part 1 section in 'if (MicrocodeEntryPoint-
> >HeaderVersion == 0x1)' section for a valid microcode data.
> 
> V2:
> 'if (MicrocodeEntryPoint->HeaderVersion == 0x1)' condition doesn't make
> sure the entry data is a valid microcode. So abandon it. Instead, make sure
> the checked data is in the microcode data range. Because the DataSize of non
> microcde data may make (MicrocodeEntryPoint + TotalSize) larger than
> 0xffffffff. For PEI driver, UINTN is 32bit and the result is overflow and it may
> be a very small value. That means the checksum check would be done out of
> the microcode range.
> 
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/Microcode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/Microcode.c
> b/UefiCpuPkg/Library/MpInitLib/Microcode.c
> index 4763dcfebe..6c0995cb0d 100644
> --- a/UefiCpuPkg/Library/MpInitLib/Microcode.c
> +++ b/UefiCpuPkg/Library/MpInitLib/Microcode.c
> @@ -1,7 +1,7 @@
>  /** @file
>    Implementation of loading microcode on processors.
> 
> -  Copyright (c) 2015 - 2018, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2015 - 2019, Intel Corporation. All rights
> + reserved.<BR>
>    SPDX-License-Identifier: BSD-2-Clause-Patent
> 
>  **/
> @@ -170,6 +170,7 @@ MicrocodeDetect (
>      /// Check overflow and whether TotalSize is aligned with 4 bytes.
>      ///
>      if ( ((UINTN)MicrocodeEntryPoint + TotalSize) > MicrocodeEnd ||
> +         ((UINTN)MicrocodeEntryPoint + TotalSize) < (UINTN)
> + CpuMpData->MicrocodePatchAddress ||
>           (TotalSize & 0x3) != 0
>         ) {
>        MicrocodeEntryPoint = (CPU_MICROCODE_HEADER *) (((UINTN)
> MicrocodeEntryPoint) + SIZE_1KB);
> --
> 2.21.0.windows.1