[PATCH] MdeModulePkg VariableSmm: Do not need check CommBufferSize buffer

* [PATCH] MdeModulePkg VariableSmm: Do not need check CommBufferSize buffer
@ 2016-12-09  6:53 Star Zeng
       [not found] ` <0C09AFA07DD0434D9E2A0C6AEB0483103B7AA442@SHSMSX104.ccr.corp.intel.com>
  0 siblings, 1 reply; 2+ messages in thread
From: Star Zeng @ 2016-12-09  6:53 UTC (permalink / raw)
  To: edk2-devel; +Cc: Star Zeng, Jiewen Yao, Jeff Fan

Current code in SmmVariableHandler() checks CommBufferSize
buffer to make sure it points to outside SMRAM in
"case SMM_VARIABLE_FUNCTION_GET_STATISTICS".

But after eaae7b33b1cf6b9f21db1636f219c2b6a8d88afd,
CommBufferSize buffer points to SMRAM that was used by
SMM core to cache CommSize from SmmCommunication protocol,
then the check will fail definitely and GET_STATISTICS
feature breaks.

In fact, do not need check CommBufferSize buffer at all
even before eaae7b33b1cf6b9f21db1636f219c2b6a8d88afd.
Before eaae7b33b1cf6b9f21db1636f219c2b6a8d88afd,
CommBufferSize buffer pointed to gSmmCorePrivate->BufferSize
that is outside SMRAM, the check will success definitely;
after eaae7b33b1cf6b9f21db1636f219c2b6a8d88afd,
CommBufferSize buffer points to local variable BufferSize
(in SMRAM) in SmmEntryPoint(), the check is not needed
definitely.

The patch is to remove the check.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
index eafb53322e8c..c714916019ef 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.c
@@ -695,11 +695,10 @@ SmmVariableHandler (
       // It is covered by previous CommBuffer check
       //
 
-      if (!SmmIsBufferOutsideSmmValid ((EFI_PHYSICAL_ADDRESS)(UINTN)CommBufferSize, sizeof(UINTN))) {
-        DEBUG ((EFI_D_ERROR, "GetStatistics: SMM communication buffer in SMRAM!\n"));
-        Status = EFI_ACCESS_DENIED;
-        goto EXIT;
-      }
+      //
+      // Do not need to check CommBufferSize buffer as it should point to SMRAM
+      // that was used by SMM core to cache CommSize from SmmCommunication protocol.
+      //
 
       Status = SmmVariableGetStatistics (VariableInfo, &InfoSize);
       *CommBufferSize = InfoSize + SMM_VARIABLE_COMMUNICATE_HEADER_SIZE;
-- 
2.7.0.windows.1



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