From a7181d952fcd0b03c423cef99b6e8bf93d9cb1f1 Mon Sep 17 00:00:00 2001
From: Jian J Wang <jian.j.wang@intel.com>
Date: Mon, 9 Oct 2017 21:58:55 +0800
Subject: [PATCH] MdeModulePkg/Core/Dxe: Add EndOfDxe workaround for NULL
 pointer detection

One of issue caused by enabling NULL pointer detection is that some PCI
device OptionROM, binary drivers and binary OS boot loaders may have NULL
pointer access bugs, which will prevent BIOS from booting and is almost
impossible to fix. BIT7 of PCD PcdNullPointerDetectionPropertyMask is used
as a workaround to indicate BIOS to disable NULL pointer detection right
after event gEfiEndOfDxeEventGroupGuid, and then let boot continue.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Ayellet Wolman <ayellet.wolman@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
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>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
---
 MdeModulePkg/Core/Dxe/DxeMain.inf             |  1 +
 MdeModulePkg/Core/Dxe/Mem/Page.c              |  4 +-
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 65 +++++++++++++++++++
 3 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
index e29d6c83ae..15f4b03d3c 100644
--- a/MdeModulePkg/Core/Dxe/DxeMain.inf
+++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
@@ -192,6 +192,7 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdPropertiesTableEnable                   ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdImageProtectionPolicy                   ## CONSUMES
   gEfiMdeModulePkgTokenSpaceGuid.PcdDxeNxMemoryProtectionPolicy             ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask        ## CONSUMES
 
 # [Hob]
 # RESOURCE_DESCRIPTOR   ## CONSUMES
diff --git a/MdeModulePkg/Core/Dxe/Mem/Page.c b/MdeModulePkg/Core/Dxe/Mem/Page.c
index 3dd6d1b4a0..c9219cc068 100644
--- a/MdeModulePkg/Core/Dxe/Mem/Page.c
+++ b/MdeModulePkg/Core/Dxe/Mem/Page.c
@@ -188,7 +188,9 @@ CoreAddRange (
   // used for other purposes.
   //  
   if (Type == EfiConventionalMemory && Start == 0 && (End >= EFI_PAGE_SIZE - 1)) {
-    SetMem ((VOID *)(UINTN)Start, EFI_PAGE_SIZE, 0);
+    if ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) == 0) {
+      SetMem ((VOID *)(UINTN)Start, EFI_PAGE_SIZE, 0);
+    }
   }
   
   //
diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index a73c4ccd64..0fa89e4437 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -995,6 +995,53 @@ MemoryProtectionExitBootServicesCallback (
   }
 }
 
+/**
+  Disable NULL pointer detection after EndOfDxe. This is a workaround resort in
+  order to skip unfixable NULL pointer access issues detected in OptionROM or
+  boot loaders.
+
+  @param[in]  Event     The Event this notify function registered to.
+  @param[in]  Context   Pointer to the context data registered to the Event.
+**/
+VOID
+EFIAPI
+DisableNullDetectionAtTheEndOfDxe (
+  EFI_EVENT                               Event,
+  VOID                                    *Context
+  )
+{
+  EFI_STATUS                        Status;
+  EFI_GCD_MEMORY_SPACE_DESCRIPTOR   Desc;
+
+  DEBUG ((DEBUG_INFO, "DisableNullDetectionAtTheEndOfDxe(): start\r\n"));
+  //
+  // Disable NULL pointer detection by enabling first 4K page
+  //
+  Status = CoreGetMemorySpaceDescriptor (0, &Desc);
+  ASSERT_EFI_ERROR (Status);
+
+  if ((Desc.Capabilities & EFI_MEMORY_RP) == 0) {
+    Status = CoreSetMemorySpaceCapabilities (
+              0,
+              EFI_PAGE_SIZE,
+              Desc.Capabilities | EFI_MEMORY_RP
+              );
+    ASSERT_EFI_ERROR (Status);
+  }
+
+  Status = CoreSetMemorySpaceAttributes (
+            0,
+            EFI_PAGE_SIZE,
+            Desc.Attributes & ~EFI_MEMORY_RP
+            );
+  ASSERT_EFI_ERROR (Status);
+
+  CoreCloseEvent (Event);
+  DEBUG ((DEBUG_INFO, "DisableNullDetectionAtTheEndOfDxe(): end\r\n"));
+
+  return;
+}
+
 /**
   Initialize Memory Protection support.
 **/
@@ -1006,6 +1053,7 @@ CoreInitializeMemoryProtection (
 {
   EFI_STATUS  Status;
   EFI_EVENT   Event;
+  EFI_EVENT   EndOfDxeEvent;
   VOID        *Registration;
 
   mImageProtectionPolicy = PcdGet32(PcdImageProtectionPolicy);
@@ -1044,6 +1092,23 @@ CoreInitializeMemoryProtection (
                );
     ASSERT_EFI_ERROR(Status);
   }
+
+  //
+  // Register a callback to disable NULL pointer detection at EndOfDxe
+  //
+  if ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & (BIT0|BIT7))
+       == (BIT0|BIT7)) {
+    Status = CoreCreateEventEx (
+                    EVT_NOTIFY_SIGNAL,
+                    TPL_NOTIFY,
+                    DisableNullDetectionAtTheEndOfDxe,
+                    NULL,
+                    &gEfiEndOfDxeEventGroupGuid,
+                    &EndOfDxeEvent
+                    );
+    ASSERT_EFI_ERROR (Status);
+  }
+
   return ;
 }
 
-- 
2.39.2