From 1bde91a85d76c5593fd7543abfac18b936ef959b Mon Sep 17 00:00:00 2001
From: Mikhail Krichanov <mikhailkrichanov@gmail.com>
Date: Fri, 29 Nov 2024 19:42:10 +0300
Subject: [PATCH] Ring3: Set 1G User pages as not present by default, fixed
 padding.

---
 MdeModulePkg/Core/Dxe/SysCall/X64/InitializeMsr.c            | 2 +-
 .../CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm      | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/SysCall/X64/InitializeMsr.c b/MdeModulePkg/Core/Dxe/SysCall/X64/InitializeMsr.c
index af451fe547..c3bcc33919 100644
--- a/MdeModulePkg/Core/Dxe/SysCall/X64/InitializeMsr.c
+++ b/MdeModulePkg/Core/Dxe/SysCall/X64/InitializeMsr.c
@@ -111,7 +111,7 @@ MakeUserPageTableTemplate (
           //
           PageDirectory1GEntry->Uint64         = (UINT64)PageAddress | PageTableInfo->AddressEncMask;
           PageDirectory1GEntry->Bits.ReadWrite = 1;
-          PageDirectory1GEntry->Bits.Present   = 1;
+          PageDirectory1GEntry->Bits.Present   = 0;
           PageDirectory1GEntry->Bits.MustBe1   = 1;
         }
       } else {
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
index 49f6267982..31e1a70780 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
@@ -63,11 +63,14 @@ global ASM_PFX(UserPageTable)
 ASM_PFX(UserPageTable):
   resq 1
 
-ALIGN   4096
 global ASM_PFX(mSwitchCr3Flag)
 ASM_PFX(mSwitchCr3Flag):
   db 0x0
 
+ALIGN   4096
+Padding:
+  db 0x0
+
 DEFAULT REL
 SECTION .text