From 0adc6eae9480ca1ae7ac01e239e09b58e447e467 Mon Sep 17 00:00:00 2001
From: Jian J Wang <jian.j.wang@intel.com>
Date: Wed, 7 Nov 2018 08:48:09 +0800
Subject: MdeModulePkg/Core: fix ineffective guard page issue

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 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 before doing related jobs.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 36 +++++++++++++--------------
 1 file changed, 17 insertions(+), 19 deletions(-)

(limited to 'MdeModulePkg/Core/Dxe')

diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index 8a93c5362a..c43e0d08ae 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -1136,26 +1136,24 @@ CoreInitializeMemoryProtection (
   ASSERT (GetPermissionAttributeForMemoryType (EfiBootServicesData) ==
           GetPermissionAttributeForMemoryType (EfiConventionalMemory));
 
-  if (mImageProtectionPolicy != 0 || PcdGet64 (PcdDxeNxMemoryProtectionPolicy) != 0) {
-    Status = CoreCreateEvent (
-               EVT_NOTIFY_SIGNAL,
-               TPL_CALLBACK,
-               MemoryProtectionCpuArchProtocolNotify,
-               NULL,
-               &Event
-               );
-    ASSERT_EFI_ERROR(Status);
+  Status = CoreCreateEvent (
+             EVT_NOTIFY_SIGNAL,
+             TPL_CALLBACK,
+             MemoryProtectionCpuArchProtocolNotify,
+             NULL,
+             &Event
+             );
+  ASSERT_EFI_ERROR(Status);
 
-    //
-    // Register for protocol notifactions on this event
-    //
-    Status = CoreRegisterProtocolNotify (
-               &gEfiCpuArchProtocolGuid,
-               Event,
-               &Registration
-               );
-    ASSERT_EFI_ERROR(Status);
-  }
+  //
+  // Register for protocol notifactions on this event
+  //
+  Status = CoreRegisterProtocolNotify (
+             &gEfiCpuArchProtocolGuid,
+             Event,
+             &Registration
+             );
+  ASSERT_EFI_ERROR(Status);
 
   //
   // Register a callback to disable NULL pointer detection at EndOfDxe
-- 
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