[edk2-devel] [PATCH v5 7/9] UefiCpuPkg/CpuMpPei: Enable paging and set NP flag to avoid TOCTOU (CVE-2019-11098)

[Guomin Jiang]

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1614

To avoid the TOCTOU, enable paging and set Not Present flag so when
access any code in the flash range, it will trigger #NP exception.

Cc: Eric Dong <eric.d...@intel.com>
Cc: Ray Ni <ray...@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Rahul Kumar <rahul1.ku...@intel.com>
Signed-off-by: Guomin Jiang <guomin.ji...@intel.com>
Acked-by: Laszlo Ersek <ler...@redhat.com>
---
 UefiCpuPkg/CpuMpPei/CpuMpPei.inf |  3 +++
 UefiCpuPkg/CpuMpPei/CpuPaging.c  | 26 ++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
index f4d11b861f77..7e511325d8b8 100644
--- a/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
+++ b/UefiCpuPkg/CpuMpPei/CpuMpPei.inf
@@ -46,6 +46,9 @@ [LibraryClasses]
   BaseMemoryLib
   CpuLib
 
+[Guids]
+  gEdkiiMigratedFvInfoGuid                                             ## 
SOMETIMES_CONSUMES     ## HOB
+
 [Ppis]
   gEfiPeiMpServicesPpiGuid                      ## PRODUCES
   gEfiSecPlatformInformationPpiGuid             ## SOMETIMES_CONSUMES
diff --git a/UefiCpuPkg/CpuMpPei/CpuPaging.c b/UefiCpuPkg/CpuMpPei/CpuPaging.c
index 3bf0574b34c6..04a16fb2b620 100644
--- a/UefiCpuPkg/CpuMpPei/CpuPaging.c
+++ b/UefiCpuPkg/CpuMpPei/CpuPaging.c
@@ -12,6 +12,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 #include <Library/MemoryAllocationLib.h>
 #include <Library/CpuLib.h>
 #include <Library/BaseLib.h>
+#include <Guid/MigratedFvInfo.h>
 
 #include "CpuMpPei.h"
 
@@ -605,6 +606,8 @@ MemoryDiscoveredPpiNotifyCallback (
   EFI_STATUS  Status;
   BOOLEAN     InitStackGuard;
   BOOLEAN     InterruptState;
+  EDKII_MIGRATED_FV_INFO *MigratedFvInfo;
+  EFI_PEI_HOB_POINTERS   Hob;
 
   if (PcdGetBool (PcdMigrateTemporaryRamFirmwareVolumes)) {
     InterruptState = SaveAndDisableInterrupts ();
@@ -619,9 +622,14 @@ MemoryDiscoveredPpiNotifyCallback (
   // the task switch (for the sake of stack switch).
   //
   InitStackGuard = FALSE;
-  if (IsIa32PaeSupported () && PcdGetBool (PcdCpuStackGuard)) {
+  Hob.Raw = NULL;
+  if (IsIa32PaeSupported ()) {
+    Hob.Raw  = GetFirstGuidHob (&gEdkiiMigratedFvInfoGuid);
+    InitStackGuard = PcdGetBool (PcdCpuStackGuard);
+  }
+
+  if (InitStackGuard || Hob.Raw != NULL) {
     EnablePaging ();
-    InitStackGuard = TRUE;
   }
 
   Status = InitializeCpuMpWorker ((CONST EFI_PEI_SERVICES **)PeiServices);
@@ -631,6 +639,20 @@ MemoryDiscoveredPpiNotifyCallback (
     SetupStackGuardPage ();
   }
 
+  while (Hob.Raw != NULL) {
+    MigratedFvInfo = GET_GUID_HOB_DATA (Hob);
+
+    //
+    // Enable #NP exception, so if the code access after disable NEM, it will 
generate
+    // to avoid potential vulnerability.
+    //
+    ConvertMemoryPageAttributes (MigratedFvInfo->FvOrgBase, 
MigratedFvInfo->FvLength, 0);
+
+    Hob.Raw = GET_NEXT_HOB (Hob);
+    Hob.Raw = GetNextGuidHob (&gEdkiiMigratedFvInfoGuid, Hob.Raw);
+  }
+  CpuFlushTlb ();
+
   return Status;
 }
 
-- 
2.25.1.windows.1


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