[PATCH 2/2] MdeModulePkg/Core: fix ineffective guard page issue

[Jian J Wang <jian.j.wang@intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1295

This issue originates from following patch which allows to enable
paging if PcdImageProtectionPolicy and PcdDxeNxMemoryProtectionPolicy
(in addition to PcdSetNxForStack) are set to enable related features.

  5267926134d17e86672b84fd57b438f05ffa68e1

Due to above change, PcdImageProtectionPolicy will be set to 0 by
default in many platforms, which, in turn, cause following code in
MdeModulePkg\Core\Dxe\Misc\MemoryProtection.c fail the creation of
notify event of CpuArchProtocol.

1138:  if (mImageProtectionPolicy != 0 ||
           PcdGet64 (PcdDxeNxMemoryProtectionPolicy) != 0) {
1139:  Status = CoreCreateEvent (
...
1142:             MemoryProtectionCpuArchProtocolNotify,
...
1145:             );

Then following call flow won't be done and Guard pages will not be
set as not-present in SetAllGuardPages() eventually.

   MemoryProtectionCpuArchProtocolNotify()
=> HeapGuardCpuArchProtocolNotify()
=> SetAllGuardPages()

The solution is removing the if(...) statement so that the notify
event will always be created and handler be registered. This won't
cause unnecessary code execution because, in the notify event handler,
the related PCDs like

    PcdImageProtectionPolicy and
    PcdDxeNxMemoryProtectionPolicy

will be checked again to do its job.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index 30e5c5153c..30798b05b9 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -1135,7 +1135,6 @@ CoreInitializeMemoryProtection (
   ASSERT (GetPermissionAttributeForMemoryType (EfiBootServicesData) ==
           GetPermissionAttributeForMemoryType (EfiConventionalMemory));
 
-  if (mImageProtectionPolicy != 0 || PcdGet64 (PcdDxeNxMemoryProtectionPolicy) != 0) {
   Status = CoreCreateEvent (
              EVT_NOTIFY_SIGNAL,
              TPL_CALLBACK,
@@ -1154,7 +1153,6 @@ CoreInitializeMemoryProtection (
              &Registration
              );
   ASSERT_EFI_ERROR(Status);
-  }
 
   //
   // Register a callback to disable NULL pointer detection at EndOfDxe
-- 
2.16.2.windows.1