From f9d0e5daa058f0cf4caa8edad0dfa2a3a390f1b0 Mon Sep 17 00:00:00 2001
From: Jian J Wang <devel@edk2.groups.io>
Date: Wed, 6 Nov 2019 21:13:32 +0000
Subject: [PATCH] MdeModulePkg/DxeIplPeim: reserve page 0 for NULL pointer
 detection

When a boot loader examines the memory map, it can see that location 0
is available memory. If it chooses to use that memory, and
PcdNullPointerDetectionPropertyMask is enabled, use of memory in page 0
will cause an exception. This does occur when running the memtest86
program.

Leaving page 0 available is for legacy support purpose. Since we have
deprecated the support of legacy, the solution is just reserving it so
that it cannot be allocated for other uses.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1885
Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
---
 MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c | 4 ++++
 MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c  | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
index 172d7cd1c6..6e8ca824d4 100644
--- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
+++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
@@ -246,8 +246,12 @@ HandOffToDxeCore (
   EFI_PEI_VECTOR_HANDOFF_INFO_PPI *VectorHandoffInfoPpi;
   BOOLEAN                   BuildPageTablesIa32Pae;
 
+  //
+  // Clear page 0 and mark it as allocated if NULL pointer detection is enabled.
+  //
   if (IsNullDetectionEnabled ()) {
     ClearFirst4KPage (HobList.Raw);
+    BuildMemoryAllocationHob (0, EFI_PAGES_TO_SIZE (1), EfiBootServicesData);
   }
 
   Status = PeiServicesAllocatePages (EfiBootServicesData, EFI_SIZE_TO_PAGES (STACK_SIZE), &BaseOfStack);
diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
index 2867610bff..f465eb1d8a 100644
--- a/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
+++ b/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
@@ -36,8 +36,12 @@ HandOffToDxeCore (
   EFI_VECTOR_HANDOFF_INFO         *VectorInfo;
   EFI_PEI_VECTOR_HANDOFF_INFO_PPI *VectorHandoffInfoPpi;
 
+  //
+  // Clear page 0 and mark it as allocated if NULL pointer detection is enabled.
+  //
   if (IsNullDetectionEnabled ()) {
     ClearFirst4KPage (HobList.Raw);
+    BuildMemoryAllocationHob (0, EFI_PAGES_TO_SIZE (1), EfiBootServicesData);
   }
 
   //