[edk2-devel] [PATCH 0/3] Fix boot failure when use secure boot supported (-D SECURE_BOOT_ENABLE=TRUE) OVMF packages

[edk2-devel] [PATCH 0/3] Fix boot failure when use secure boot supported (-D SECURE_BOOT_ENABLE=TRUE) OVMF packages

[wojiaohanliyang]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4807

This patch series provides fixes for boot VM when use secure boot
supported (-D SECURE_BOOT_ENABLE=TRUE) OVMF packages.

- Detect FlashNvVarStore before calls PlaformValidateNvVarStore in PlatformInitLib
  and skip the validation process if the FlashNvVarStore doesn't exist. Since the
  PlatformValidateNvVarStore will return false if the FlashNvVarStore doesn't
  exist, this will trigger ASSERT (FALSE) and prevent the guest from moving
  forward.

- Init the whole range of EmuVariableNvStore before copy content from the
  FlashNvVarStore to EmuVariableNvStore. If the Ftw (Fault Tolerant Write) part
  of the EmuVariableNvStore isn't initialized, the FaultToleranteWriteDxe will
  use scrambled address to access memory and leads to crash if the VM is a
  SEV guest.

- Fix the mapping for FlashNvVarStore. If launch a SEV VM with only OVMF.fd,
  the address range for FlashNvVarStore should be mapped as encrypted before
  access FlashNvVarStore in PlatformValidateNvVarStore. If launch a SEV VM with
  both OVMF_CODE.fd and OVMF_VARS.fd, the address range for FlashNvVarStore
  should be mapped as decrypted before access FlashNvVarStore in
  PlatformValidateNvVarStore.

---

These patches based on commit:
d4dbe5e101dc ("SecurityPkg/Tcg2Acpi: Revise debug print")

Han Liyang (3):
 OvmfPkg/PlatformPei: Update mapping of FlashNvVarStore before validate it
 OvmfPkg/PlatformInitLib: Init the EmuVariableNvStore before copy data
 OvmfPkg/PlatformInitLib: Detect FlashNvVarStore before validate it

OvmfPkg/Library/PlatformInitLib/Platform.c | 67 +++++++++++
OvmfPkg/Library/PlatformInitLib/PlatformInitLib.inf | 1 +
OvmfPkg/PlatformPei/AmdSev.c | 105 ++++++++++++++++++
OvmfPkg/PlatformPei/Platform.c | 6 +
OvmfPkg/PlatformPei/Platform.h | 6 +
OvmfPkg/PlatformPei/PlatformPei.inf | 1 +
6 files changed, 186 insertions(+)

-- 
2.25.1



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[edk2-devel] [PATCH 1/3] OvmfPkg/PlatformInitLib: Detect FlashNvVarStore before validate it

[wojiaohanliyang]

From: hanliyang <wojiaohanliyang@163.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4807

The commit 4f173db8b45b ("OvmfPkg/PlatformInitLib: Add functions for
EmuVariableNvStore") rename the function from TdxValidateCfv to
PlatformValidateNvVarStore.

PlatformValidateNvVarStore is placed in the PlatformInitLib and is used
in the case that OVMF is launched with -bios parameter and to validate
the integrity of FlashNvVarStore. But if we launch a VM without
FlashNvVarStore, the PlatformValidateNvVarStore will fail to validate
the integrity and will trigger ASSERT (FALSE) in
PlatformInitEmuVariableNvStore.

In order to prevent calls to PlatformValidateNvVarStore in the case lack
of FlashNvVarStore, we should detect FlashNvVarStore before calls to
PlatformValidateNvVarStore. If fail to detect FlashNvVarStore, we should
return don't initialize the EmuVariableNvStore, otherwise calls to
PlatformValidateNvVarStore and initialize the EmuVariableNvStore when
succeed to validate the integrity of NvVarStore.

Fixes: 4f173db8b45b ("OvmfPkg/PlatformInitLib: Add functions for EmuVariableNvStore")
Signed-off-by: hanliyang <wojiaohanliyang@163.com>
---
 OvmfPkg/Library/PlatformInitLib/Platform.c    | 47 +++++++++++++++++++
 .../PlatformInitLib/PlatformInitLib.inf       |  1 +
 2 files changed, 48 insertions(+)

diff --git a/OvmfPkg/Library/PlatformInitLib/Platform.c b/OvmfPkg/Library/PlatformInitLib/Platform.c
index f48bf16ae3..0a720a4c2c 100644
--- a/OvmfPkg/Library/PlatformInitLib/Platform.c
+++ b/OvmfPkg/Library/PlatformInitLib/Platform.c
@@ -895,6 +895,16 @@ PlatformReserveEmuVariableNvStore (
   return VariableStore;
 }
 
+#define WRITE_BYTE_CMD           0x10
+#define BLOCK_ERASE_CMD          0x20
+#define CLEAR_STATUS_CMD         0x50
+#define READ_STATUS_CMD          0x70
+#define READ_DEVID_CMD           0x90
+#define BLOCK_ERASE_CONFIRM_CMD  0xd0
+#define READ_ARRAY_CMD           0xff
+
+#define CLEARED_ARRAY_STATUS  0x00
+
 /**
  When OVMF is lauched with -bios parameter, UEFI variables will be
  partially emulated, and non-volatile variables may lose their contents
@@ -928,6 +938,43 @@ PlatformInitEmuVariableNvStore (
   Size = (UINT32)PcdGet32 (PcdFlashNvStorageVariableSize);
   ASSERT (Size < EmuVariableNvStoreSize);
 
+  //
+  // If launch a VM without OvmfFlashNvStorage device, then we'll fail
+  // to check the integrity of NvVarStore and trigger ASSERT (FALSE).
+  // So, we should detect the OvmfFlashNvStorage before calls to
+  // PlatformValidateNvVarStore(). If fail to detect OvmfFlashNvStorage,
+  // we should return and don't initialize the EmuVariableNvStore,
+  // otherwise calls to PlatformValidateNvVarStore() and initialize the
+  // EmuVariableNvStore when succeed to check the integrity of
+  // NvVarStore.
+  //
+  // This method to detect the OvmfFlashNvStorage here references
+  // OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c.
+  //
+  volatile UINT8  *Ptr;
+
+  UINTN  BlockSize;
+  UINTN  Offset;
+  UINT8  ProbeUint8;
+
+  BlockSize = PcdGet32 (PcdOvmfFirmwareBlockSize);
+
+  for (Offset = 0; Offset < BlockSize; Offset++) {
+    Ptr        = Base + Offset;
+    ProbeUint8 = *Ptr;
+    if ((ProbeUint8 != CLEAR_STATUS_CMD) &&
+        (ProbeUint8 != READ_STATUS_CMD) &&
+        (ProbeUint8 != CLEARED_ARRAY_STATUS))
+    {
+      break;
+    }
+  }
+
+  if (Offset >= BlockSize) {
+    DEBUG ((DEBUG_INFO, "OvmfFlashNvStorage: Failed to find probe location\n"));
+    return EFI_INVALID_PARAMETER;
+  }
+
   if (!PlatformValidateNvVarStore (Base, PcdGet32 (PcdCfvRawDataSize))) {
     ASSERT (FALSE);
     return EFI_INVALID_PARAMETER;
diff --git a/OvmfPkg/Library/PlatformInitLib/PlatformInitLib.inf b/OvmfPkg/Library/PlatformInitLib/PlatformInitLib.inf
index 21e6efa5e0..b7d5e63dcd 100644
--- a/OvmfPkg/Library/PlatformInitLib/PlatformInitLib.inf
+++ b/OvmfPkg/Library/PlatformInitLib/PlatformInitLib.inf
@@ -104,6 +104,7 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdTdxAcceptPageSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashNvStorageVariableBase
   gUefiOvmfPkgTokenSpaceGuid.PcdCfvRawDataSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFirmwareBlockSize
 
 [FeaturePcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdDxeIplSwitchToLongMode
-- 
2.25.1



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[edk2-devel] [PATCH 2/3] OvmfPkg/PlatformInitLib: Init the EmuVariableNvStore before copy data

[wojiaohanliyang]

From: hanliyang <wojiaohanliyang@163.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4807

In the case launch with just OVMF.fd, if we just init part of the
EmuVariableNvStore, then EmuVariableFvbRuntimeDxe will skip the
initialize process of the EmuVariableNvStore and the Ftw (Fault
Tolerant Write) part of the EmuVariableNvStore will not be
initialized before the Ftw part is accessed. When we launch a SEV
guest, the FaultTolerantWriteDxe will get scrambled data when read
Ftw part of the EmuVariableNvStore, the FaultToleranteWriteDxe
access address specified by the scrambled data will cause invalid
address access and crash. The crash message is shown as below.

Loading driver at 0x000BDB92000 EntryPoint=0x000BDB95EF4 FaultTolerantWriteDxe.efi
InstallProtocolInterface: BC62157E-3E33-4FEC-9920-2D3B36D750DF BDE01D98
ProtectUefiImageCommon - 0xBDE01040
  - 0x00000000BDB92000 - 0x0000000000005B00
Ftw: FtwWorkSpaceLba - 0x40, WorkBlockSize  - 0x1000, FtwWorkSpaceBase - 0x0
Ftw: FtwSpareLba     - 0x42, SpareBlockSize - 0x1000
Ftw: NumberOfWorkBlock - 0x1, FtwWorkBlockLba - 0x40
Ftw: WorkSpaceLbaInSpare - 0x0, WorkSpaceBaseInSpare - 0x0
Ftw: Remaining work space size - FE0
!!!! X64 Exception Type - 0D(#GP - General Protection)  CPU Apic ID - 00000000 !!!!
ExceptionData - 0000000000000000
RIP  - 00000000BDB92459, CS  - 0000000000000038, RFLAGS - 0000000000010286
RAX  - 587E3201A019FB0C, RCX - 587E3200E238F994, RDX - 0000000000000001
RBX  - 00000000BDE10018, RSP - 00000000BFB79AD8, RBP - 0000000000000FE0
RSI  - 00000000BDE100A8, RDI - 00000000BDE10128
R8   - D4642A9DFB7C79BE, R9  - 00000000000003F8, R10 - 00000000BDB96602
R11  - 0000000000000002, R12 - 00000000BDE100A0, R13 - 0000000000000000
R14  - 0000000000000001, R15 - 00000000BFBA76C0
DS   - 0000000000000030, ES  - 0000000000000030, FS  - 0000000000000030
GS   - 0000000000000030, SS  - 0000000000000030
CR0  - 0000000080010033, CR2 - 0000000000000000, CR3 - 00000000BF801000
CR4  - 0000000000000668, CR8 - 0000000000000000
DR0  - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000
DR3  - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400
GDTR - 00000000BF5DC000 0000000000000047, LDTR - 0000000000000000
IDTR - 00000000BEF0C018 0000000000000FFF,   TR - 0000000000000000
FXSAVE_STATE - 00000000BFB79730
!!!! Find image based on IP(0xBDB92459) /dev/shm/edk2/Build/OvmfX64/DEBUG_GCC5/X64/MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteDxe/DEBUG/FaultTolerantWriteDxe.dll (ImageBase=00000000BDB92000, EntryPoint=00000000BDB95EF4) !!!!

Fixes: 4f173db8b45b ("OvmfPkg/PlatformInitLib: Add functions for EmuVariableNvStore")
Signed-off-by: hanliyang <wojiaohanliyang@163.com>
---
 OvmfPkg/Library/PlatformInitLib/Platform.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/OvmfPkg/Library/PlatformInitLib/Platform.c b/OvmfPkg/Library/PlatformInitLib/Platform.c
index 0a720a4c2c..5dbc5506f4 100644
--- a/OvmfPkg/Library/PlatformInitLib/Platform.c
+++ b/OvmfPkg/Library/PlatformInitLib/Platform.c
@@ -905,6 +905,8 @@ PlatformReserveEmuVariableNvStore (
 
 #define CLEARED_ARRAY_STATUS  0x00
 
+#define ERASED_UINT8  0xff
+
 /**
  When OVMF is lauched with -bios parameter, UEFI variables will be
  partially emulated, and non-volatile variables may lose their contents
@@ -982,6 +984,24 @@ PlatformInitEmuVariableNvStore (
 
   DEBUG ((DEBUG_INFO, "Init EmuVariableNvStore with the content in FlashNvStorage\n"));
 
+  //
+  // Init the whole EmuVariableNvStore before copy the content from
+  // FlashNvStorage to the EmuVariableNvStore.
+  //
+  // In the case launch with just OVMF.fd, if we just init part of the
+  // EmuVariableNvStore, then EmuVariableFvbRuntimeDxe will skip the
+  // initialize process of the EmuVariableNvStore and the Ftw (Fault
+  // Tolerant Write) part of the EmuVariableNvStore will not be
+  // initialized before the Ftw part is accessed. When we launch a SEV
+  // guest, the FaultTolerantWriteDxe will get scrambled data when read
+  // Ftw part of the EmuVariableNvStore, the FaultToleranteWriteDxe
+  // access address specified by the scrambled data will cause invalid
+  // address access and crash.
+  //
+  // The method to init EmuVariableNvStore here references
+  // OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.c.
+  //
+  SetMem (EmuVariableNvStore, EmuVariableNvStoreSize, ERASED_UINT8);
   CopyMem (EmuVariableNvStore, Base, Size);
 
   return EFI_SUCCESS;
-- 
2.25.1



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[edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Update mapping of FlashNvVarStore before validate it

[wojiaohanliyang]

From: hanliyang <wojiaohanliyang@163.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4807

In the case of launch a SEV-ES VM with just OVMF_CODE.fd, the validation
process in PlatformValidateNvVarStore will trigger MMIO NPF, and the #VC
handler will detect that mmio access is invalid because the mmio address
range of FlashNvVarStore is mapped as encrypted.

In the case of launch a SEV VM with both OVMF_CODE.fd and OVMF_VARS.fd,
PlatformValidateNvVarStore will fail to validate FlashNvVarStore because
the mapping of FlashNvVarStore address range is encrypted in the guest
but the corresponding data in system physical memory was not encrypted
by guest key.

We should map FlashNvVarStore address range as unencrypted for the above
cases.

Fixes: 4f173db8b45b ("OvmfPkg/PlatformInitLib: Add functions for EmuVariableNvStore")
Signed-off-by: hanliyang <wojiaohanliyang@163.com>
---
 OvmfPkg/PlatformPei/AmdSev.c        | 105 ++++++++++++++++++++++++++++
 OvmfPkg/PlatformPei/Platform.c      |   6 ++
 OvmfPkg/PlatformPei/Platform.h      |   6 ++
 OvmfPkg/PlatformPei/PlatformPei.inf |   1 +
 4 files changed, 118 insertions(+)

diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
index 8562787035..89f4c02b6a 100644
--- a/OvmfPkg/PlatformPei/AmdSev.c
+++ b/OvmfPkg/PlatformPei/AmdSev.c
@@ -575,3 +575,108 @@ SevInitializeRam (
       );
   }
 }
+
+/**
+  Prepared for FlashNvVarStore access.
+
+  **/
+VOID
+SevFlashNvVarStoreUpdateMapping (
+  IN UINTN  NvVarStoreBase,
+  IN UINTN  NvVarStoreSize
+  )
+{
+  volatile UINT8  *Ptr;
+
+  RETURN_STATUS  DecEncStatus;
+  UINT8          Offset;
+
+  DEBUG ((DEBUG_INFO, "%a\n", __func__));
+
+  if (!MemEncryptSevIsEnabled ()) {
+    return;
+  }
+
+  //
+  // In the case of launch a SEV-ES VM with just OVMF_CODE.fd, the
+  // validation process in PlatformValidateNvVarStore will trigger MMIO
+  // NPF, and the #VC handler will detect that mmio access is invalid
+  // because the mmio address range of FlashNvVarStore is mapped as
+  // encrypted. So, first we should update the mapping of address range
+  // of FlashNvVarStore as decrypted.
+  //
+  DEBUG (
+         (
+          DEBUG_INFO,
+          "%a: mapping FlashNvVarStore address range unencrypted [0x%p - 0x%p]\n",
+          __func__,
+          (UINT8 *)NvVarStoreBase,
+          (UINT8 *)NvVarStoreBase + NvVarStoreSize - 1
+         )
+         );
+
+  DecEncStatus = MemEncryptSevClearMmioPageEncMask (
+                                                    0,
+                                                    NvVarStoreBase,
+                                                    EFI_SIZE_TO_PAGES (NvVarStoreSize)
+                                                    );
+  if (RETURN_ERROR (DecEncStatus)) {
+    DEBUG (
+           (
+            DEBUG_ERROR,
+            "%a: failed to map FlashNvStorage address range unencrypted\n",
+            __func__
+           )
+           );
+    ASSERT_RETURN_ERROR (DecEncStatus);
+  }
+
+  //
+  // Here, the first 16 bytes of FlashNvVarStore will be all zeros in
+  // the following cases:
+  //     a. Launch VM with just OVMF_CODE.fd
+  //     b. Launch VM with OVMF_CODE.fd and OVMF_VARS.fd
+  // In these cases, the access of FlashNvVarStore will be as expected.
+  //
+  // But if launch VM with just OVMF.fd, the first 16 bytes of
+  // FlashNvVarStore will be scrambled data because the data of
+  // FlashNvVarStore are encrypted by SEV API. In this case, we need
+  // mapping FlashNvVarStore address range as encrypted again, otherwise
+  // the validation of FlashNvVarStore will fail and trigger
+  // ASSERT (FALSE).
+  //
+  for (Offset = 0; Offset < 16; Offset++) {
+    Ptr = (UINT8 *)NvVarStoreBase + Offset;
+    if (*Ptr) {
+      break;
+    }
+  }
+
+  if (Offset == 16) {
+    return;
+  }
+
+  DEBUG (
+         (
+          DEBUG_INFO,
+          "%a: mapping FlashNvStorage address range encrypted\n",
+          __func__
+         )
+         );
+
+  DecEncStatus = MemEncryptSevSetPageEncMask (
+                                              0,
+                                              NvVarStoreBase,
+                                              EFI_SIZE_TO_PAGES (NvVarStoreSize)
+                                              );
+  if (RETURN_ERROR (DecEncStatus)) {
+    DEBUG (
+           (
+            DEBUG_ERROR,
+            "%a: failed to map FlashNvStorage address range encrypted\n",
+            __func__
+           )
+           );
+    ASSERT_RETURN_ERROR (DecEncStatus);
+  }
+}
diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index 0114529778..bcb18dacac 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -224,6 +224,12 @@ ReserveEmuVariableNvStore (
   PcdStatus     = PcdSet64S (PcdEmuVariableNvStoreReserved, VariableStore);
 
   if (FeaturePcdGet (PcdSecureBootSupported)) {
+    // update mapping of FlashNvVarStore address range
+    SevFlashNvVarStoreUpdateMapping (
+                                     PcdGet32 (PcdOvmfFlashNvStorageVariableBase),
+                                     2 * PcdGet32 (PcdFlashNvStorageFtwSpareSize)
+                                     );
+
     // restore emulated VarStore from pristine ROM copy
     PlatformInitEmuVariableNvStore ((VOID *)(UINTN)VariableStore);
   }
diff --git a/OvmfPkg/PlatformPei/Platform.h b/OvmfPkg/PlatformPei/Platform.h
index 0a59547cfc..b8ad8df1dc 100644
--- a/OvmfPkg/PlatformPei/Platform.h
+++ b/OvmfPkg/PlatformPei/Platform.h
@@ -111,4 +111,10 @@ SevInitializeRam (
   VOID
   );
 
+VOID
+SevFlashNvVarStoreUpdateMapping (
+  IN UINTN  NvVarStoreBase,
+  IN UINTN  NvVarStoreSize
+  );
+
 #endif // _PLATFORM_PEI_H_INCLUDED_
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 0bb1a46291..a3dd3db72d 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -139,6 +139,7 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashNvStorageVariableBase
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
-- 
2.25.1



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[edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Update mapping of FlashNvVarStore before validate it

[wojiaohanliyang]

From: hanliyang <wojiaohanliyang@163.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4807

In the case of launch a SEV-ES VM with just OVMF_CODE.fd, the validation
process in PlatformValidateNvVarStore will trigger MMIO NPF, and the #VC
handler will detect that mmio access is invalid because the mmio address
range of FlashNvVarStore is mapped as encrypted.

In the case of launch a SEV VM with both OVMF_CODE.fd and OVMF_VARS.fd,
PlatformValidateNvVarStore will fail to validate FlashNvVarStore because
the mapping of FlashNvVarStore address range is encrypted in the guest
but the corresponding data in system physical memory was not encrypted
by guest key.

We should map FlashNvVarStore address range as unencrypted for the above
cases.

Fixes: 4f173db8b45b ("OvmfPkg/PlatformInitLib: Add functions for EmuVariableNvStore")
Signed-off-by: hanliyang <wojiaohanliyang@163.com>
---
 OvmfPkg/PlatformPei/AmdSev.c        | 105 ++++++++++++++++++++++++++++
 OvmfPkg/PlatformPei/Platform.c      |   6 ++
 OvmfPkg/PlatformPei/Platform.h      |   6 ++
 OvmfPkg/PlatformPei/PlatformPei.inf |   1 +
 4 files changed, 118 insertions(+)

diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
index 8562787035..89f4c02b6a 100644
--- a/OvmfPkg/PlatformPei/AmdSev.c
+++ b/OvmfPkg/PlatformPei/AmdSev.c
@@ -575,3 +575,108 @@ SevInitializeRam (
       );
   }
 }
+
+/**
+  Prepared for FlashNvVarStore access.
+
+  **/
+VOID
+SevFlashNvVarStoreUpdateMapping (
+  IN UINTN  NvVarStoreBase,
+  IN UINTN  NvVarStoreSize
+  )
+{
+  volatile UINT8  *Ptr;
+
+  RETURN_STATUS  DecEncStatus;
+  UINT8          Offset;
+
+  DEBUG ((DEBUG_INFO, "%a\n", __func__));
+
+  if (!MemEncryptSevIsEnabled ()) {
+    return;
+  }
+
+  //
+  // In the case of launch a SEV-ES VM with just OVMF_CODE.fd, the
+  // validation process in PlatformValidateNvVarStore will trigger MMIO
+  // NPF, and the #VC handler will detect that mmio access is invalid
+  // because the mmio address range of FlashNvVarStore is mapped as
+  // encrypted. So, first we should update the mapping of address range
+  // of FlashNvVarStore as decrypted.
+  //
+  DEBUG (
+         (
+          DEBUG_INFO,
+          "%a: mapping FlashNvVarStore address range unencrypted [0x%p - 0x%p]\n",
+          __func__,
+          (UINT8 *)NvVarStoreBase,
+          (UINT8 *)NvVarStoreBase + NvVarStoreSize - 1
+         )
+         );
+
+  DecEncStatus = MemEncryptSevClearMmioPageEncMask (
+                                                    0,
+                                                    NvVarStoreBase,
+                                                    EFI_SIZE_TO_PAGES (NvVarStoreSize)
+                                                    );
+  if (RETURN_ERROR (DecEncStatus)) {
+    DEBUG (
+           (
+            DEBUG_ERROR,
+            "%a: failed to map FlashNvStorage address range unencrypted\n",
+            __func__
+           )
+           );
+    ASSERT_RETURN_ERROR (DecEncStatus);
+  }
+
+  //
+  // Here, the first 16 bytes of FlashNvVarStore will be all zeros in
+  // the following cases:
+  //     a. Launch VM with just OVMF_CODE.fd
+  //     b. Launch VM with OVMF_CODE.fd and OVMF_VARS.fd
+  // In these cases, the access of FlashNvVarStore will be as expected.
+  //
+  // But if launch VM with just OVMF.fd, the first 16 bytes of
+  // FlashNvVarStore will be scrambled data because the data of
+  // FlashNvVarStore are encrypted by SEV API. In this case, we need
+  // mapping FlashNvVarStore address range as encrypted again, otherwise
+  // the validation of FlashNvVarStore will fail and trigger
+  // ASSERT (FALSE).
+  //
+  for (Offset = 0; Offset < 16; Offset++) {
+    Ptr = (UINT8 *)NvVarStoreBase + Offset;
+    if (*Ptr) {
+      break;
+    }
+  }
+
+  if (Offset == 16) {
+    return;
+  }
+
+  DEBUG (
+         (
+          DEBUG_INFO,
+          "%a: mapping FlashNvStorage address range encrypted\n",
+          __func__
+         )
+         );
+
+  DecEncStatus = MemEncryptSevSetPageEncMask (
+                                              0,
+                                              NvVarStoreBase,
+                                              EFI_SIZE_TO_PAGES (NvVarStoreSize)
+                                              );
+  if (RETURN_ERROR (DecEncStatus)) {
+    DEBUG (
+           (
+            DEBUG_ERROR,
+            "%a: failed to map FlashNvStorage address range encrypted\n",
+            __func__
+           )
+           );
+    ASSERT_RETURN_ERROR (DecEncStatus);
+  }
+}
diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index 0114529778..bcb18dacac 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -224,6 +224,12 @@ ReserveEmuVariableNvStore (
   PcdStatus     = PcdSet64S (PcdEmuVariableNvStoreReserved, VariableStore);
 
   if (FeaturePcdGet (PcdSecureBootSupported)) {
+    // update mapping of FlashNvVarStore address range
+    SevFlashNvVarStoreUpdateMapping (
+                                     PcdGet32 (PcdOvmfFlashNvStorageVariableBase),
+                                     2 * PcdGet32 (PcdFlashNvStorageFtwSpareSize)
+                                     );
+
     // restore emulated VarStore from pristine ROM copy
     PlatformInitEmuVariableNvStore ((VOID *)(UINTN)VariableStore);
   }
diff --git a/OvmfPkg/PlatformPei/Platform.h b/OvmfPkg/PlatformPei/Platform.h
index 0a59547cfc..b8ad8df1dc 100644
--- a/OvmfPkg/PlatformPei/Platform.h
+++ b/OvmfPkg/PlatformPei/Platform.h
@@ -111,4 +111,10 @@ SevInitializeRam (
   VOID
   );
 
+VOID
+SevFlashNvVarStoreUpdateMapping (
+  IN UINTN  NvVarStoreBase,
+  IN UINTN  NvVarStoreSize
+  );
+
 #endif // _PLATFORM_PEI_H_INCLUDED_
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 0bb1a46291..a3dd3db72d 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -139,6 +139,7 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpSecretsSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashNvStorageVariableBase
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
-- 
2.25.1



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