[edk2-devel] [PATCH 1/5] MdeModulePkg: avoid SMM pointers being leaked by not using CopyMem()

[Michael D Kinney]

Zhiguang,

An implementation of CopyGuid() could use CopyMem().
Does CopyGuid() also need to be avoided?

Mike

> -----Original Message-----
> From: devel at edk2.groups.io <devel at edk2.groups.io> On
> Behalf Of Zhiguang Liu
> Sent: Tuesday, June 16, 2020 2:05 AM
> To: devel at edk2.groups.io
> Cc: Zeng, Star <star.zeng at intel.com>; Gao, Liming
> <liming.gao at intel.com>; Wang, Jian J
> <jian.j.wang at intel.com>; Wu, Hao A <hao.a.wu at intel.com>
> Subject: [edk2-devel] [PATCH 1/5] MdeModulePkg: avoid
> SMM pointers being leaked by not using CopyMem()
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2002
> 
> This commit will update the logic in function
> SmmVariableGetStatistics()
> so that the pointer fields ('Next' and 'Name') in
> structure
> VARIABLE_INFO_ENTRY will not be copied into the SMM
> communication buffer.
> 
> Doing so will prevent SMM pointers address from being
> leaked into non-SMM
> environment.
> 
> Please note that newly introduced internal function
> CopyVarInfoEntry()
> will not use CopyMem() to copy the whole
> VARIABLE_INFO_ENTRY structure and
> then zero out the 'Next' and 'Name' fields. This is for
> preventing race
> conditions where the pointers value might still be read.
> 
> Cc: Star Zeng <star.zeng at intel.com>
> Cc: Liming Gao <liming.gao at intel.com>
> Cc: Jian J Wang <jian.j.wang at intel.com>
> Signed-off-by: Hao A Wu <hao.a.wu at intel.com>
> Signed-off-by: Zhiguang Liu <zhiguang.liu at intel.com>
> ---
> 
> MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git
> a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm
> .c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm
> .c
> index caca5c3241..74e756bc00 100644
> ---
> a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm
> .c
> +++
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm
> .c
> @@ -315,6 +315,35 @@ GetFvbCountAndBuffer (
>  }
> 
> 
> 
> 
> 
> +/**
> 
> +  Copy only the meaningful fields of the variable
> statistics information from
> 
> +  source buffer to the destination buffer. Other fields
> are filled with zero.
> 
> +
> 
> +  @param[out]  DstInfoEntry    A pointer to the buffer
> of destination variable
> 
> +                               information entry.
> 
> +  @param[in]   SrcInfoEntry    A pointer to the buffer
> of source variable
> 
> +                               information entry.
> 
> +
> 
> +**/
> 
> +static
> 
> +VOID
> 
> +CopyVarInfoEntry (
> 
> +  OUT VARIABLE_INFO_ENTRY    *DstInfoEntry,
> 
> +  IN  VARIABLE_INFO_ENTRY    *SrcInfoEntry
> 
> +  )
> 
> +{
> 
> +  DstInfoEntry->Next = NULL;
> 
> +  DstInfoEntry->Name = NULL;
> 
> +
> 
> +  CopyGuid (&DstInfoEntry->VendorGuid, &SrcInfoEntry-
> >VendorGuid);
> 
> +  DstInfoEntry->Attributes  = SrcInfoEntry->Attributes;
> 
> +  DstInfoEntry->ReadCount   = SrcInfoEntry->ReadCount;
> 
> +  DstInfoEntry->WriteCount  = SrcInfoEntry->WriteCount;
> 
> +  DstInfoEntry->DeleteCount = SrcInfoEntry-
> >DeleteCount;
> 
> +  DstInfoEntry->CacheCount  = SrcInfoEntry->CacheCount;
> 
> +  DstInfoEntry->Volatile    = SrcInfoEntry->Volatile;
> 
> +}
> 
> +
> 
>  /**
> 
>    Get the variable statistics information from the
> information buffer pointed by gVariableInfo.
> 
> 
> 
> @@ -377,7 +406,7 @@ SmmVariableGetStatistics (
>        *InfoSize = StatisticsInfoSize;
> 
>        return EFI_BUFFER_TOO_SMALL;
> 
>      }
> 
> -    CopyMem (InfoEntry, VariableInfo, sizeof
> (VARIABLE_INFO_ENTRY));
> 
> +    CopyVarInfoEntry (InfoEntry, VariableInfo);
> 
>      CopyMem (InfoName, VariableInfo->Name, NameSize);
> 
>      *InfoSize = StatisticsInfoSize;
> 
>      return EFI_SUCCESS;
> 
> @@ -417,7 +446,7 @@ SmmVariableGetStatistics (
>      return EFI_BUFFER_TOO_SMALL;
> 
>    }
> 
> 
> 
> -  CopyMem (InfoEntry, VariableInfo, sizeof
> (VARIABLE_INFO_ENTRY));
> 
> +  CopyVarInfoEntry (InfoEntry, VariableInfo);
> 
>    CopyMem (InfoName, VariableInfo->Name, NameSize);
> 
>    *InfoSize = StatisticsInfoSize;
> 
> 
> 
> --
> 2.25.1.windows.1
> 
> 
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