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

["Wu, Hao A" <hao.a.wu@intel.com>]

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