[edk2-devel] [PATCH RFC v2 26/28] OvmfPkg/MemEncryptSevLib: Change the page state in the RMP table

[Brijesh Singh]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

The MemEncryptSev{Set,Clear}PageEncMask() functions are used to set or
clear the memory encryption attribute in the page table. When SEV-SNP
is active, we also need to change the page state in the RMP table so that
it is in sync with the memory encryption attribute change.

Cc: James Bottomley <jejb at linux.ibm.com>
Cc: Min Xu <min.m.xu at intel.com>
Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Tom Lendacky <thomas.lendacky at amd.com>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Erdem Aktas <erdemaktas at google.com>
Signed-off-by: Brijesh Singh <brijesh.singh at amd.com>
---
 OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf   |  1 +
 OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c | 34 ++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
index 2158e1cba3..f613bb314f 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
@@ -51,6 +51,7 @@
   DebugLib
   MemoryAllocationLib
   PcdLib
+  VmgExitLib
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
index 996a319b26..9cca8efecb 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
@@ -17,6 +17,7 @@
 #include <Register/Cpuid.h>
 
 #include "VirtualMemory.h"
+#include "SnpPageStateChange.h"
 
 STATIC BOOLEAN mAddressEncMaskChecked = FALSE;
 STATIC UINT64  mAddressEncMask;
@@ -697,10 +698,12 @@ SetMemoryEncDec (
   PAGE_MAP_AND_DIRECTORY_POINTER *PageDirectoryPointerEntry;
   PAGE_TABLE_1G_ENTRY            *PageDirectory1GEntry;
   PAGE_TABLE_ENTRY               *PageDirectory2MEntry;
+  PHYSICAL_ADDRESS               OrigPhysicalAddress;
   PAGE_TABLE_4K_ENTRY            *PageTableEntry;
   UINT64                         PgTableMask;
   UINT64                         AddressEncMask;
   BOOLEAN                        IsWpEnabled;
+  UINTN                          OrigLength;
   RETURN_STATUS                  Status;
 
   //
@@ -753,6 +756,22 @@ SetMemoryEncDec (
 
   Status = EFI_SUCCESS;
 
+  //
+  // To maintain the security gurantees we must set the page to shared in the RMP
+  // table before clearing the memory encryption mask from the current page table.
+  //
+  // The InternalSetPageState() is used for setting the page state in the RMP table.
+  //
+  if (!Mmio && (Mode == ClearCBit) && MemEncryptSevSnpIsEnabled ()) {
+    InternalSetPageState (PhysicalAddress, EFI_SIZE_TO_PAGES (Length), SevSnpPageShared, FALSE);
+  }
+
+  //
+  // Save the specified length and physical address (we need it later).
+  //
+  OrigLength = Length;
+  OrigPhysicalAddress = PhysicalAddress;
+
   while (Length != 0)
   {
     //
@@ -925,6 +944,21 @@ SetMemoryEncDec (
   //
   CpuFlushTlb();
 
+  //
+  // SEV-SNP requires that all the private pages (i.e pages mapped encrypted) must be
+  // added in the RMP table (as a private) before the access.
+  //
+  // The InternalSetPageState() is used for setting the page state in the RMP table.
+  //
+  if (!Mmio && (Mode == SetCBit) && MemEncryptSevSnpIsEnabled ()) {
+    InternalSetPageState (
+      OrigPhysicalAddress,
+      EFI_SIZE_TO_PAGES (OrigLength),
+      SevSnpPagePrivate,
+      FALSE
+      );
+  }
+
 Done:
   //
   // Restore page table write protection, if any.
-- 
2.17.1



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