Re: [edk2-devel] [PATCH v2] MdeModulePkg/Variable/RuntimeDxe: Not copy SMM pointers in comm buffer

["Wang, Jian J" <jian.j.wang@intel.com>]

This is still a security bug fix, which needs CVE number added in title. With it
addressed,

Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

> -----Original Message-----
> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of
> Wu, Hao A
> Sent: Wednesday, August 07, 2019 8:18 AM
> To: devel@edk2.groups.io
> Cc: Wu, Hao A <hao.a.wu@intel.com>; Zeng, Star <star.zeng@intel.com>;
> Gao, Liming <liming.gao@intel.com>; Wang, Jian J <jian.j.wang@intel.com>
> Subject: [edk2-devel] [PATCH v2] MdeModulePkg/Variable/RuntimeDxe:
> Not copy SMM pointers in comm buffer
> 
> 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@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Signed-off-by: Hao A Wu <hao.a.wu@intel.com>
> ---
> 
> V2 patch updates the type of parameter 'DstInfoEntry' from 'in' to 'out'
> for the newly added function CopyVarInfoEntry().
> 
> 
>  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 ec463d063e..9b59387e58 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
> @@ -312,6 +312,35 @@ 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.
> 
>    Caution: This function may be invoked at SMM runtime.
> @@ -373,7 +402,7 @@ 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;
> @@ -413,7 +442,7 @@ SmmVariableGetStatistics (
>      return EFI_BUFFER_TOO_SMALL;
>    }
> 
> -  CopyMem (InfoEntry, VariableInfo, sizeof (VARIABLE_INFO_ENTRY));
> +  CopyVarInfoEntry (InfoEntry, VariableInfo);
>    CopyMem (InfoName, VariableInfo->Name, NameSize);
>    *InfoSize = StatisticsInfoSize;
> 
> --
> 2.12.0.windows.1
> 
> 
>