From 0bbed0664ff117d2ad371f074e08502d3021a9dc Mon Sep 17 00:00:00 2001
From: Tom Lendacky <thomas.lendacky@amd.com>
Date: Wed, 12 Aug 2020 15:21:40 -0500
Subject: [PATCH] OvmfPkg/PlatformPei: Reserve GHCB-related areas if S3 is
 supported

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

Protect the memory used by an SEV-ES guest when S3 is supported. This
includes the page table used to break down the 2MB page that contains
the GHCB so that it can be marked un-encrypted, as well as the GHCB
area.

Regarding the lifecycle of the GHCB-related memory areas:
  PcdOvmfSecGhcbPageTableBase
  PcdOvmfSecGhcbBase

(a) when and how it is initialized after first boot of the VM

  If SEV-ES is enabled, the GHCB-related areas are initialized during
  the SEC phase [OvmfPkg/ResetVector/Ia32/PageTables64.asm].

(b) how it is protected from memory allocations during DXE

  If S3 and SEV-ES are enabled, then InitializeRamRegions()
  [OvmfPkg/PlatformPei/MemDetect.c] protects the ranges with an AcpiNVS
  memory allocation HOB, in PEI.

  If S3 is disabled, then these ranges are not protected. DXE's own page
  tables are first built while still in PEI (see HandOffToDxeCore()
  [MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c]). Those tables are
  located in permanent PEI memory. After CR3 is switched over to them
  (which occurs before jumping to the DXE core entry point), we don't have
  to preserve PcdOvmfSecGhcbPageTableBase. PEI switches to GHCB pages in
  permanent PEI memory and DXE will use these PEI GHCB pages, so we don't
  have to preserve PcdOvmfSecGhcbBase.

(c) how it is protected from the OS

  If S3 is enabled, then (b) reserves it from the OS too.

  If S3 is disabled, then the range needs no protection.

(d) how it is accessed on the S3 resume path

  It is rewritten same as in (a), which is fine because (b) reserved it.

(e) how it is accessed on the warm reset path

  It is rewritten same as in (a).

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien@xen.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/PlatformPei/MemDetect.c     | 23 +++++++++++++++++++++++
 OvmfPkg/PlatformPei/PlatformPei.inf |  4 ++++
 2 files changed, 27 insertions(+)

diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index 3b46ea431a..6b5fee166b 100644
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -27,6 +27,7 @@ Module Name:
 #include <Library/DebugLib.h>
 #include <Library/HobLib.h>
 #include <Library/IoLib.h>
+#include <Library/MemEncryptSevLib.h>
 #include <Library/PcdLib.h>
 #include <Library/PciLib.h>
 #include <Library/PeimEntryPoint.h>
@@ -866,6 +867,28 @@ InitializeRamRegions (
       (UINT64)(UINTN) PcdGet32 (PcdOvmfSecPageTablesSize),
       EfiACPIMemoryNVS
       );
+
+    if (MemEncryptSevEsIsEnabled ()) {
+      //
+      // If SEV-ES is enabled, reserve the GHCB-related memory area. This
+      // includes the extra page table used to break down the 2MB page
+      // mapping into 4KB page entries where the GHCB resides and the
+      // GHCB area itself.
+      //
+      // Since this memory range will be used by the Reset Vector on S3
+      // resume, it must be reserved as ACPI NVS.
+      //
+      BuildMemoryAllocationHob (
+        (EFI_PHYSICAL_ADDRESS)(UINTN) PcdGet32 (PcdOvmfSecGhcbPageTableBase),
+        (UINT64)(UINTN) PcdGet32 (PcdOvmfSecGhcbPageTableSize),
+        EfiACPIMemoryNVS
+        );
+      BuildMemoryAllocationHob (
+        (EFI_PHYSICAL_ADDRESS)(UINTN) PcdGet32 (PcdOvmfSecGhcbBase),
+        (UINT64)(UINTN) PcdGet32 (PcdOvmfSecGhcbSize),
+        EfiACPIMemoryNVS
+        );
+    }
 #endif
   }
 
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 00feb96c93..a54d10ba90 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -75,6 +75,10 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfLockBoxStorageBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfLockBoxStorageSize
   gUefiOvmfPkgTokenSpaceGuid.PcdGuidedExtractHandlerTableSize