MdePkg/BaseLib: Add Shadow Stack Support for X86.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1521

This patch adds SSP - shadow stack pointer to JumpBuffer.
It will be used for the platform that enabled CET/ShadowStack.

We add gEfiMdePkgTokenSpaceGuid.PcdControlFlowEnforcementPropertyMask
to control the global enable/disable.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yao Jiewen <jiewen.yao@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>

MdePkg/Library/BaseLib/X64/SetJump.nasm

@@ -1,6 +1,6 @@
 ;------------------------------------------------------------------------------
 ;
-; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2006 - 2019, 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
@@ -19,10 +19,13 @@
 ;
 ;------------------------------------------------------------------------------
 
+%include "Nasm.inc"
+
     DEFAULT REL
     SECTION .text
 
 extern ASM_PFX(InternalAssertJumpBuffer)
+extern ASM_PFX(PcdGet32 (PcdControlFlowEnforcementPropertyMask))
 
 ;------------------------------------------------------------------------------
 ; UINTN
@@ -39,6 +42,24 @@ ASM_PFX(SetJump):
     add     rsp, 0x20
     pop     rcx
     pop     rdx
+
+    xor     rax, rax
+    mov     [rcx + 0xF8], rax            ; save 0 to SSP
+
+    mov     eax, [ASM_PFX(PcdGet32 (PcdControlFlowEnforcementPropertyMask))]
+    test    eax, eax
+    jz      CetDone
+    mov     rax, cr4
+    bt      eax, 23                      ; check if CET is enabled
+    jnc     CetDone
+
+    mov     rax, 1
+    INCSSP_RAX                           ; to read original SSP
+    READSSP_RAX
+    mov     [rcx + 0xF8], rax            ; save SSP
+
+CetDone:
+
     mov     [rcx], rbx
     mov     [rcx + 8], rsp
     mov     [rcx + 0x10], rbp