[PATCH 1/2] MdeModulePkg/Core: Refine handling NULL detection in NX setting

[Hao Wu <hao.a.wu@intel.com>]

The commit rewrites the logic in function
InitializeDxeNxMemoryProtectionPolicy() for handling the first page
(page 0) when NULL pointer detection feature is enabled.

Instead of skip setting the page 0, the codes will now override the
attribute setting of page 0 by adding the 'EFI_MEMORY_RP' attribute.

The purpose is to make it easy for other special handlings of pages
(e.g. the first page of the stack when stack guard feature is enabled).

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@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: Hao Wu <hao.a.wu@intel.com>
---
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index 455ed35f9a..a2ea445eef 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -19,7 +19,7 @@
 
   Once the image is unloaded, the protection is removed automatically.
 
-Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2017 - 2018, Intel Corporation. All rights reserved.<BR>
 This program and the accompanying materials
 are licensed and made available under the terms and conditions of the BSD License
 which accompanies this distribution.  The full text of the license may be found at
@@ -846,23 +846,23 @@ InitializeDxeNxMemoryProtectionPolicy (
 
     Attributes = GetPermissionAttributeForMemoryType (MemoryMapEntry->Type);
     if (Attributes != 0) {
+      SetUefiImageMemoryAttributes (
+        MemoryMapEntry->PhysicalStart,
+        LShiftU64 (MemoryMapEntry->NumberOfPages, EFI_PAGE_SHIFT),
+        Attributes);
+
       if (MemoryMapEntry->PhysicalStart == 0 &&
           PcdGet8 (PcdNullPointerDetectionPropertyMask) != 0) {
 
         ASSERT (MemoryMapEntry->NumberOfPages > 0);
         //
-        // Skip page 0 if NULL pointer detection is enabled to avoid attributes
-        // overwritten.
+        // Add EFI_MEMORY_RP attribute for page 0 if NULL pointer detection is
+        // enabled.
         //
         SetUefiImageMemoryAttributes (
-          MemoryMapEntry->PhysicalStart + EFI_PAGE_SIZE,
-          LShiftU64 (MemoryMapEntry->NumberOfPages - 1, EFI_PAGE_SHIFT),
-          Attributes);
-      } else {
-        SetUefiImageMemoryAttributes (
-          MemoryMapEntry->PhysicalStart,
-          LShiftU64 (MemoryMapEntry->NumberOfPages, EFI_PAGE_SHIFT),
-          Attributes);
+          0,
+          EFI_PAGES_TO_SIZE (1),
+          EFI_MEMORY_RP | Attributes);
       }
     }
     MemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
-- 
2.12.0.windows.1