From 9280f16345755708ebd9553b3caee077ade0e592 Mon Sep 17 00:00:00 2001
From: Oliver Smith-Denny <osde@microsoft.com>
Date: Tue, 17 Jun 2025 15:26:47 -0700
Subject: [PATCH] UefiPayloadPkg: Don't Allocate Page 0

UefiPayloadPkg has copied the MdeModulePkg DxeIpl behavior to
create a memory allocation HOB for page 0. That is being changed
(see that commit for details), so also remove it here.

Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>
---
 .../UefiPayloadEntry/Ia32/DxeLoadFunc.c       |  8 ---
 .../UefiPayloadEntry/Ia32/DxeLoadFuncFit.c    |  8 ---
 .../UefiPayloadEntry/X64/DxeLoadFunc.c        |  8 ---
 .../UefiPayloadEntry/X64/DxeLoadFuncFit.c     |  8 ---
 .../UefiPayloadEntry/X64/VirtualMemory.c      | 66 -------------------
 5 files changed, 98 deletions(-)

diff --git a/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFunc.c b/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFunc.c
index 6009232524..3391da8446 100644
--- a/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFunc.c
+++ b/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFunc.c
@@ -280,14 +280,6 @@ HandOffToDxeCore (
   IoWrite8 (LEGACY_8259_MASK_REGISTER_MASTER, 0xFF);
   IoWrite8 (LEGACY_8259_MASK_REGISTER_SLAVE, 0xFF);
 
-  //
-  // 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);
-  }
-
   BaseOfStack = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePages (EFI_SIZE_TO_PAGES (STACK_SIZE));
   ASSERT (BaseOfStack != 0);
 
diff --git a/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFuncFit.c b/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFuncFit.c
index 439d5bee0b..d0f3143004 100644
--- a/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFuncFit.c
+++ b/UefiPayloadPkg/UefiPayloadEntry/Ia32/DxeLoadFuncFit.c
@@ -278,14 +278,6 @@ HandOffToDxeCore (
   IoWrite8 (LEGACY_8259_MASK_REGISTER_MASTER, 0xFF);
   IoWrite8 (LEGACY_8259_MASK_REGISTER_SLAVE, 0xFF);
 
-  //
-  // 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);
-  }
-
   BaseOfStack = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePages (EFI_SIZE_TO_PAGES (STACK_SIZE));
   ASSERT (BaseOfStack != 0);
 
diff --git a/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFunc.c b/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFunc.c
index 6c3603f120..6672740e47 100644
--- a/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFunc.c
+++ b/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFunc.c
@@ -52,14 +52,6 @@ HandOffToDxeCore (
   IoWrite8 (LEGACY_8259_MASK_REGISTER_MASTER, 0xFF);
   IoWrite8 (LEGACY_8259_MASK_REGISTER_SLAVE, 0xFF);
 
-  //
-  // 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);
-  }
-
   //
   // Allocate 128KB for the Stack
   //
diff --git a/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFuncFit.c b/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFuncFit.c
index 35b52a911d..37528d5fe2 100644
--- a/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFuncFit.c
+++ b/UefiPayloadPkg/UefiPayloadEntry/X64/DxeLoadFuncFit.c
@@ -53,14 +53,6 @@ HandOffToDxeCore (
   IoWrite8 (LEGACY_8259_MASK_REGISTER_MASTER, 0xFF);
   IoWrite8 (LEGACY_8259_MASK_REGISTER_SLAVE, 0xFF);
 
-  //
-  // 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);
-  }
-
   //
   // Allocate 128KB for the Stack
   //
diff --git a/UefiPayloadPkg/UefiPayloadEntry/X64/VirtualMemory.c b/UefiPayloadPkg/UefiPayloadEntry/X64/VirtualMemory.c
index bfe1ba4d02..9e45ef31d9 100644
--- a/UefiPayloadPkg/UefiPayloadEntry/X64/VirtualMemory.c
+++ b/UefiPayloadPkg/UefiPayloadEntry/X64/VirtualMemory.c
@@ -37,72 +37,6 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 //
 PAGE_TABLE_POOL  *mPageTablePool = NULL;
 
-/**
-  Clear legacy memory located at the first 4K-page, if available.
-
-  This function traverses the whole HOB list to check if memory from 0 to 4095
-  exists and has not been allocated, and then clear it if so.
-
-  @param HobStart                  The start of HobList passed to DxeCore.
-
-**/
-VOID
-ClearFirst4KPage (
-  IN  VOID  *HobStart
-  )
-{
-  EFI_PEI_HOB_POINTERS  RscHob;
-  EFI_PEI_HOB_POINTERS  MemHob;
-  BOOLEAN               DoClear;
-
-  RscHob.Raw = HobStart;
-  MemHob.Raw = HobStart;
-  DoClear    = FALSE;
-
-  //
-  // Check if page 0 exists and free
-  //
-  while ((RscHob.Raw = GetNextHob (
-                         EFI_HOB_TYPE_RESOURCE_DESCRIPTOR,
-                         RscHob.Raw
-                         )) != NULL)
-  {
-    if ((RscHob.ResourceDescriptor->ResourceType == EFI_RESOURCE_SYSTEM_MEMORY) &&
-        (RscHob.ResourceDescriptor->PhysicalStart == 0))
-    {
-      DoClear = TRUE;
-      //
-      // Make sure memory at 0-4095 has not been allocated.
-      //
-      while ((MemHob.Raw = GetNextHob (
-                             EFI_HOB_TYPE_MEMORY_ALLOCATION,
-                             MemHob.Raw
-                             )) != NULL)
-      {
-        if (MemHob.MemoryAllocation->AllocDescriptor.MemoryBaseAddress
-            < EFI_PAGE_SIZE)
-        {
-          DoClear = FALSE;
-          break;
-        }
-
-        MemHob.Raw = GET_NEXT_HOB (MemHob);
-      }
-
-      break;
-    }
-
-    RscHob.Raw = GET_NEXT_HOB (RscHob);
-  }
-
-  if (DoClear) {
-    DEBUG ((DEBUG_INFO, "Clearing first 4K-page!\r\n"));
-    SetMem (NULL, EFI_PAGE_SIZE, 0);
-  }
-
-  return;
-}
-
 /**
   Return configure status of NULL pointer detection feature.