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

[Zhiguang Liu]

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.z...@intel.com>
Cc: Liming Gao <liming....@intel.com>
Cc: Jian J Wang <jian.j.w...@intel.com>
Signed-off-by: Hao A Wu <hao.a...@intel.com>
Signed-off-by: Zhiguang Liu <zhiguang....@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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