MdeModulePkg/PiSmmCore: SmmEntryPoint underflow (CVE-2021-38578)

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3387

Added use of SafeIntLib to validate values are not causing overflows or
underflows in user controlled values when calculating buffer sizes.

Signed-off-by: Miki Demeter <[email protected]>
Reviewed-by: Michael D Kinney <[email protected]>
Cc: Jian J Wang <[email protected]>
Cc: Liming Gao <[email protected]>
Reviewed-by: Liming Gao <[email protected]>

Author: miki-intel-work

MdeModulePkg/Core/PiSmmCore/PiSmmCore.c

@@ -610,6 +610,7 @@ SmmEndOfS3ResumeHandler (
   @param[in] Size2  Size of Buff2
 
   @retval TRUE      Buffers overlap in memory.
+  @retval TRUE      Math error.     Prevents potential math over and underflows.
   @retval FALSE     Buffer doesn't overlap.
 
 **/
@@ -621,11 +622,24 @@ InternalIsBufferOverlapped (
   IN UINTN  Size2
   )
 {
+  UINTN    End1;
+  UINTN    End2;
+  BOOLEAN  IsOverUnderflow1;
+  BOOLEAN  IsOverUnderflow2;
+
+  // Check for over or underflow
+  IsOverUnderflow1 = EFI_ERROR (SafeUintnAdd ((UINTN)Buff1, Size1, &End1));
+  IsOverUnderflow2 = EFI_ERROR (SafeUintnAdd ((UINTN)Buff2, Size2, &End2));
+
+  if (IsOverUnderflow1 || IsOverUnderflow2) {
+    return TRUE;
+  }
+
   //
   // If buff1's end is less than the start of buff2, then it's ok.
   // Also, if buff1's start is beyond buff2's end, then it's ok.
   //
-  if (((Buff1 + Size1) <= Buff2) || (Buff1 >= (Buff2 + Size2))) {
+  if ((End1 <= (UINTN)Buff2) || ((UINTN)Buff1 >= End2)) {
     return FALSE;
   }
 
@@ -651,6 +665,7 @@ SmmEntryPoint (
   EFI_SMM_COMMUNICATE_HEADER  *CommunicateHeader;
   BOOLEAN                     InLegacyBoot;
   BOOLEAN                     IsOverlapped;
+  BOOLEAN                     IsOverUnderflow;
   VOID                        *CommunicationBuffer;
   UINTN                       BufferSize;
 
@@ -699,23 +714,31 @@ SmmEntryPoint (
                        (UINT8 *)gSmmCorePrivate,
                        sizeof (*gSmmCorePrivate)
                        );
-      if (!SmmIsBufferOutsideSmmValid ((UINTN)CommunicationBuffer, BufferSize) || IsOverlapped) {
+      //
+      // Check for over or underflows
+      //
+      IsOverUnderflow = EFI_ERROR (SafeUintnSub (BufferSize, OFFSET_OF (EFI_SMM_COMMUNICATE_HEADER, Data), &BufferSize));
+
+      if (!SmmIsBufferOutsideSmmValid ((UINTN)CommunicationBuffer, BufferSize) ||
+          IsOverlapped || IsOverUnderflow)
+      {
         //
         // If CommunicationBuffer is not in valid address scope,
         // or there is overlap between gSmmCorePrivate and CommunicationBuffer,
+        // or there is over or underflow,
         // return EFI_INVALID_PARAMETER
         //
         gSmmCorePrivate->CommunicationBuffer = NULL;
         gSmmCorePrivate->ReturnStatus        = EFI_ACCESS_DENIED;
       } else {
         CommunicateHeader = (EFI_SMM_COMMUNICATE_HEADER *)CommunicationBuffer;
-        BufferSize       -= OFFSET_OF (EFI_SMM_COMMUNICATE_HEADER, Data);
-        Status            = SmiManage (
-                              &CommunicateHeader->HeaderGuid,
-                              NULL,
-                              CommunicateHeader->Data,
-                              &BufferSize
-                              );
+        // BufferSize was updated by the SafeUintnSub() call above.
+        Status = SmiManage (
+                   &CommunicateHeader->HeaderGuid,
+                   NULL,
+                   CommunicateHeader->Data,
+                   &BufferSize
+                   );
         //
         // Update CommunicationBuffer, BufferSize and ReturnStatus
         // Communicate service finished, reset the pointer to CommBuffer to NULL

MdeModulePkg/Core/PiSmmCore/PiSmmCore.h

@@ -54,6 +54,7 @@
 #include <Library/PerformanceLib.h>
 #include <Library/HobLib.h>
 #include <Library/SmmMemLib.h>
+#include <Library/SafeIntLib.h>
 
 #include "PiSmmCorePrivateData.h"
 #include "HeapGuard.h"

MdeModulePkg/Core/PiSmmCore/PiSmmCore.inf

@@ -60,6 +60,7 @@
   PerformanceLib
   HobLib
   SmmMemLib
+  SafeIntLib
 
 [Protocols]
   gEfiDxeSmmReadyToLockProtocolGuid             ## UNDEFINED # SmiHandlerRegister

MdeModulePkg/Core/PiSmmCore/PiSmmIpl.c

@@ -34,8 +34,8 @@
 #include <Library/UefiRuntimeLib.h>
 #include <Library/PcdLib.h>
 #include <Library/ReportStatusCodeLib.h>
-
 #include "PiSmmCorePrivateData.h"
+#include <Library/SafeIntLib.h>
 
 #define SMRAM_CAPABILITIES  (EFI_MEMORY_WB | EFI_MEMORY_UC)
 
@@ -1354,6 +1354,7 @@ SmmSplitSmramEntry (
   @param[in] ReservedRangeToCompare     Pointer to EFI_SMM_RESERVED_SMRAM_REGION to compare.
 
   @retval TRUE  There is overlap.
+  @retval TRUE  Math error.
   @retval FALSE There is no overlap.
 
 **/
@@ -1363,11 +1364,29 @@ SmmIsSmramOverlap (
   IN EFI_SMM_RESERVED_SMRAM_REGION  *ReservedRangeToCompare
   )
 {
-  UINT64  RangeToCompareEnd;
-  UINT64  ReservedRangeToCompareEnd;
-
-  RangeToCompareEnd         = RangeToCompare->CpuStart + RangeToCompare->PhysicalSize;
-  ReservedRangeToCompareEnd = ReservedRangeToCompare->SmramReservedStart + ReservedRangeToCompare->SmramReservedSize;
+  UINT64   RangeToCompareEnd;
+  UINT64   ReservedRangeToCompareEnd;
+  BOOLEAN  IsOverUnderflow1;
+  BOOLEAN  IsOverUnderflow2;
+
+  // Check for over or underflow.
+  IsOverUnderflow1 = EFI_ERROR (
+                       SafeUint64Add (
+                         (UINT64)RangeToCompare->CpuStart,
+                         RangeToCompare->PhysicalSize,
+                         &RangeToCompareEnd
+                         )
+                       );
+  IsOverUnderflow2 = EFI_ERROR (
+                       SafeUint64Add (
+                         (UINT64)ReservedRangeToCompare->SmramReservedStart,
+                         ReservedRangeToCompare->SmramReservedSize,
+                         &ReservedRangeToCompareEnd
+                         )
+                       );
+  if (IsOverUnderflow1 || IsOverUnderflow2) {
+    return TRUE;
+  }
 
   if ((RangeToCompare->CpuStart >= ReservedRangeToCompare->SmramReservedStart) &&
       (RangeToCompare->CpuStart < ReservedRangeToCompareEnd))

MdeModulePkg/Core/PiSmmCore/PiSmmIpl.inf

@@ -46,6 +46,7 @@
   DxeServicesLib
   PcdLib
   ReportStatusCodeLib
+  SafeIntLib
 
 [Protocols]
   gEfiSmmBase2ProtocolGuid                      ## PRODUCES