[PATCH v8 28/32] 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: Michael Roth <michael.roth@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
.../X64/PeiDxeVirtualMemory.c | 34 +++++++++++++++++++
1 file changed, 34 insertions(+)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
index f146f6d61cc5..56db1e4b6ecf 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;
@@ -695,10 +696,12 @@ 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;

//
@@ -751,6 +754,22 @@ 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 ((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)
{
//
@@ -923,6 +942,21 @@ SetMemoryEncDec (
//
CpuFlushTlb();

+ //
+ // SEV-SNP requires that all the private pages (i.e pages mapped encrypted) must be
+ // added in the RMP table before the access.
+ //
+ // The InternalSetPageState() is used for setting the page state in the RMP table.
+ //
+ if ((Mode == SetCBit) && MemEncryptSevSnpIsEnabled ()) {
+ InternalSetPageState (
+ OrigPhysicalAddress,
+ EFI_SIZE_TO_PAGES (OrigLength),
+ SevSnpPagePrivate,
+ FALSE
+ );
+ }
+
Done:
//
// Restore page table write protection, if any.
--
2.25.1