[edk2-devel] [PATCH v3] OvmfPkg: Don't make APIC MMIO accesses with encryption bit set

["Roth, Michael via groups.io" <Michael.Roth=amd.com@groups.io>]

For the most part, OVMF will clear the encryption bit for MMIO regions,
but there is currently one known exception during SEC when the APIC
base address is accessed via MMIO with the encryption bit set for
SEV-ES/SEV-SNP guests. In the case of SEV-SNP, this requires special
handling on the hypervisor side which may not be available in the
future[1], so make the necessary changes in the SEC-configured page
table to clear the encryption bit for 4K region containing the APIC
base address.

Since CpuPageTableLib is used to handle the splitting, some additional
care must be taken to clear the C-bit in all non-leaf PTEs since the
library expects that to be the case. Add handling for that when setting
up the SEC page table.

While here, drop special handling for the APIC base address in the
SEV-ES/SNP #VC handler.

[1] https://lore.kernel.org/lkml/20240208002420.34mvemnzrwwsaesw@amd.com/#t

Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jianyong Wu <jianyong.wu@arm.com>
Cc: Anatol Belski <anbelski@linux.microsoft.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
v3:
  - also clear C-bit for non-leaf PTEs containing GHCB range
  - add missing Cc's to commit log
v2:
  - use CpuPageTableLib to handle splitting (Gerd, Tom)

 OvmfPkg/AmdSev/AmdSevX64.fdf                |  5 +-
 OvmfPkg/Bhyve/BhyveX64.dsc                  |  1 +
 OvmfPkg/CloudHv/CloudHvX64.fdf              |  5 +-
 OvmfPkg/Library/CcExitLib/CcExitVcHandler.c | 12 +----
 OvmfPkg/Microvm/MicrovmX64.fdf              |  3 ++
 OvmfPkg/OvmfPkg.dec                         |  5 ++
 OvmfPkg/OvmfPkgX64.fdf                      |  5 +-
 OvmfPkg/ResetVector/Ia32/AmdSev.asm         |  5 +-
 OvmfPkg/ResetVector/Ia32/PageTables64.asm   | 20 +++----
 OvmfPkg/Sec/AmdSev.c                        | 58 +++++++++++++++++++++
 OvmfPkg/Sec/AmdSev.h                        | 14 +++++
 OvmfPkg/Sec/SecMain.c                       |  1 +
 OvmfPkg/Sec/SecMain.inf                     |  3 ++
 13 files changed, 112 insertions(+), 25 deletions(-)

diff --git a/OvmfPkg/AmdSev/AmdSevX64.fdf b/OvmfPkg/AmdSev/AmdSevX64.fdf
index d49555c6c8..595945181c 100644
--- a/OvmfPkg/AmdSev/AmdSevX64.fdf
+++ b/OvmfPkg/AmdSev/AmdSevX64.fdf
@@ -77,7 +77,10 @@ gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase|gUefiOvmfPkgTokenSpaceGuid.Pcd
 0x010C00|0x000400
 gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableSize
 
-0x011000|0x00F000
+0x011000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize
+
+0x012000|0x00E000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
 0x020000|0x0E0000
diff --git a/OvmfPkg/Bhyve/BhyveX64.dsc b/OvmfPkg/Bhyve/BhyveX64.dsc
index 6f305d690d..78050959f8 100644
--- a/OvmfPkg/Bhyve/BhyveX64.dsc
+++ b/OvmfPkg/Bhyve/BhyveX64.dsc
@@ -174,6 +174,7 @@
   PeiHardwareInfoLib|OvmfPkg/Library/HardwareInfoLib/PeiHardwareInfoLib.inf
   DxeHardwareInfoLib|OvmfPkg/Library/HardwareInfoLib/DxeHardwareInfoLib.inf
   ImagePropertiesRecordLib|MdeModulePkg/Library/ImagePropertiesRecordLib/ImagePropertiesRecordLib.inf
+  CpuPageTableLib|UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableLib.inf
 
   CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf
   FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf
diff --git a/OvmfPkg/CloudHv/CloudHvX64.fdf b/OvmfPkg/CloudHv/CloudHvX64.fdf
index eae3ada191..3e6688b103 100644
--- a/OvmfPkg/CloudHv/CloudHvX64.fdf
+++ b/OvmfPkg/CloudHv/CloudHvX64.fdf
@@ -76,7 +76,10 @@ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCp
 0x00F000|0x001000
 gUefiOvmfPkgTokenSpaceGuid.PcdXenPvhStartOfDayStructPtr|gUefiOvmfPkgTokenSpaceGuid.PcdXenPvhStartOfDayStructPtrSize
 
-0x010000|0x010000
+0x010000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize
+
+0x011000|0x00F000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
 0x020000|0x0E0000
diff --git a/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c b/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
index 549375dfed..da8f1e5db9 100644
--- a/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
+++ b/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
@@ -98,7 +98,7 @@ UnsupportedExit (
   Validate that the MMIO memory access is not to encrypted memory.
 
   Examine the pagetable entry for the memory specified. MMIO should not be
-  performed against encrypted memory. MMIO to the APIC page is always allowed.
+  performed against encrypted memory.
 
   @param[in] Ghcb           Pointer to the Guest-Hypervisor Communication Block
   @param[in] MemoryAddress  Memory address to validate
@@ -118,16 +118,6 @@ ValidateMmioMemory (
 {
   MEM_ENCRYPT_SEV_ADDRESS_RANGE_STATE  State;
   GHCB_EVENT_INJECTION                 GpEvent;
-  UINTN                                Address;
-
-  //
-  // Allow APIC accesses (which will have the encryption bit set during
-  // SEC and PEI phases).
-  //
-  Address = MemoryAddress & ~(SIZE_4KB - 1);
-  if (Address == GetLocalApicBaseAddress ()) {
-    return 0;
-  }
 
   State = MemEncryptSevGetAddressRangeState (
             0,
diff --git a/OvmfPkg/Microvm/MicrovmX64.fdf b/OvmfPkg/Microvm/MicrovmX64.fdf
index 825bf9f5e4..055e659a35 100644
--- a/OvmfPkg/Microvm/MicrovmX64.fdf
+++ b/OvmfPkg/Microvm/MicrovmX64.fdf
@@ -62,6 +62,9 @@ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvm
 0x00C000|0x001000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupSize
 
+0x00D000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize
+
 0x010000|0x010000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
index 2f7bded926..b23219ebd4 100644
--- a/OvmfPkg/OvmfPkg.dec
+++ b/OvmfPkg/OvmfPkg.dec
@@ -277,6 +277,11 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase|0|UINT32|0x44
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupSize|0|UINT32|0x45
 
+  ## Specify the extra page table needed to mark the APIC MMIO range as unencrypted.
+  #  The value should be a multiple of 4KB for each.
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase|0x0|UINT32|0x72
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize|0x0|UINT32|0x73
+
   ## The base address and size of the SEV Launch Secret Area provisioned
   #  after remote attestation.  If this is set in the .fdf, the platform
   #  is responsible for protecting the area from DXE phase overwrites.
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index c2d3cc901e..b6e8f43566 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -97,7 +97,10 @@ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCpuidBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfCp
 0x00F000|0x001000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecSvsmCaaBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecSvsmCaaSize
 
-0x010000|0x010000
+0x010000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize
+
+0x011000|0x00F000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
 0x020000|0x0E0000
diff --git a/OvmfPkg/ResetVector/Ia32/AmdSev.asm b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
index 23e4c5ebbe..827c874312 100644
--- a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
+++ b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
@@ -162,11 +162,14 @@ SevClearPageEncMaskForGhcbPage:
     ;
     ; The initial GHCB will live at GHCB_BASE and needs to be un-encrypted.
     ; This requires the 2MB page for this range be broken down into 512 4KB
-    ; pages.  All will be marked encrypted, except for the GHCB.
+    ; pages.  All will be marked encrypted, except for the GHCB. Since the
+    ; original PMD entry is no longer a leaf entry, remove the encryption
+    ; bit when pointing to the PTE page.
     ;
     mov     ecx, (GHCB_BASE >> 21)
     mov     eax, GHCB_PT_ADDR + PAGE_PDP_ATTR
     mov     [ecx * 8 + PT_ADDR (0x2000)], eax
+    mov     [ecx * 8 + PT_ADDR (0x2000) + 4], strict dword 0
 
     ;
     ; Page Table Entries (512 * 4KB entries => 2MB)
diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
index 474d22dbfa..d913a39d46 100644
--- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
+++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
@@ -67,7 +67,7 @@ BITS    32
 ;
 ; Create page tables for 4-level paging
 ;
-; Argument: upper 32 bits of the page table entries
+; Argument: upper 32 bits of the leaf page table entries
 ;
 %macro CreatePageTables4Level 1
 
@@ -78,19 +78,19 @@ BITS    32
     ; Top level Page Directory Pointers (1 * 512GB entry)
     ;
     mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (4)], %1
+    mov     dword[PT_ADDR (4)], 0
 
     ;
     ; Next level Page Directory Pointers (4 * 1GB entries => 4GB)
     ;
     mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x2000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x1004)], %1
+    mov     dword[PT_ADDR (0x1004)], 0
     mov     dword[PT_ADDR (0x1008)], PT_ADDR (0x3000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x100C)], %1
+    mov     dword[PT_ADDR (0x100C)], 0
     mov     dword[PT_ADDR (0x1010)], PT_ADDR (0x4000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x1014)], %1
+    mov     dword[PT_ADDR (0x1014)], 0
     mov     dword[PT_ADDR (0x1018)], PT_ADDR (0x5000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x101C)], %1
+    mov     dword[PT_ADDR (0x101C)], 0
 
     ;
     ; Page Table Entries (2048 * 2MB entries => 4GB)
@@ -141,7 +141,7 @@ BITS    32
 ;
 ; Create page tables for 5-level paging with gigabyte pages
 ;
-; Argument: upper 32 bits of the page table entries
+; Argument: upper 32 bits of the leaf page table entries
 ;
 ; We have 6 pages available for the early page tables,
 ; we use four of them:
@@ -164,15 +164,15 @@ BITS    32
 
     ; level 5
     mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (4)], %1
+    mov     dword[PT_ADDR (4)], 0
 
     ; level 4
     mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x3000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x1004)], %1
+    mov     dword[PT_ADDR (0x1004)], 0
 
     ; level 3 (1x -> level 2, 3x 1GB)
     mov     dword[PT_ADDR (0x3000)], PT_ADDR (0x2000) + PAGE_PDE_DIRECTORY_ATTR
-    mov     dword[PT_ADDR (0x3004)], %1
+    mov     dword[PT_ADDR (0x3004)], 0
     mov     dword[PT_ADDR (0x3008)], (1 << 30) + PAGE_PDE_LARGEPAGE_ATTR
     mov     dword[PT_ADDR (0x300c)], %1
     mov     dword[PT_ADDR (0x3010)], (2 << 30) + PAGE_PDE_LARGEPAGE_ATTR
diff --git a/OvmfPkg/Sec/AmdSev.c b/OvmfPkg/Sec/AmdSev.c
index 520b125132..89fba2fd18 100644
--- a/OvmfPkg/Sec/AmdSev.c
+++ b/OvmfPkg/Sec/AmdSev.c
@@ -8,7 +8,10 @@
 **/
 
 #include <Library/BaseLib.h>
+#include <Library/CpuLib.h>
+#include <Library/CpuPageTableLib.h>
 #include <Library/DebugLib.h>
+#include <Library/LocalApicLib.h>
 #include <Library/MemEncryptSevLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Register/Amd/Ghcb.h>
@@ -301,3 +304,58 @@ SecValidateSystemRam (
     MemEncryptSevSnpPreValidateSystemRam (Start, EFI_SIZE_TO_PAGES ((UINTN)(End - Start)));
   }
 }
+
+/**
+  Map known MMIO regions unencrypted if SEV-ES is active.
+
+  During early booting, page table entries default to having the encryption bit
+  set for SEV-ES/SEV-SNP guests. In cases where there is MMIO to an address, the
+  encryption bit should be cleared. Clear it here for any known MMIO accesses
+  during SEC, which is currently just the APIC base address.
+
+**/
+VOID
+SecMapApicBaseUnencrypted (
+  VOID
+  )
+{
+  PHYSICAL_ADDRESS    Cr3;
+  UINT64              ApicAddress;
+  VOID                *Buffer;
+  UINTN               BufferSize;
+  IA32_MAP_ATTRIBUTE  MapAttribute;
+  IA32_MAP_ATTRIBUTE  MapMask;
+  RETURN_STATUS       Status;
+
+  if (!SevEsIsEnabled ()) {
+    return;
+  }
+
+  ApicAddress = (UINT64)GetLocalApicBaseAddress ();
+  Buffer      = (VOID *)(UINTN)FixedPcdGet32 (PcdOvmfSecApicPageTableBase);
+  Cr3         = AsmReadCr3 ();
+
+  MapAttribute.Uint64         = ApicAddress;
+  MapAttribute.Bits.Present   = 1;
+  MapAttribute.Bits.ReadWrite = 1;
+  MapMask.Uint64              = MAX_UINT64;
+  BufferSize                  = SIZE_4KB;
+
+  Status = PageTableMap (
+             (UINTN *)&Cr3,
+             Paging4Level,
+             Buffer,
+             &BufferSize,
+             ApicAddress,
+             SIZE_4KB,
+             &MapAttribute,
+             &MapMask,
+             NULL
+             );
+  if (RETURN_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR, "Failed to map APIC MMIO region as unencrypted: %d\n", Status));
+    ASSERT (FALSE);
+  }
+
+  CpuFlushTlb ();
+}
diff --git a/OvmfPkg/Sec/AmdSev.h b/OvmfPkg/Sec/AmdSev.h
index f75877096e..c5ab0d5a0b 100644
--- a/OvmfPkg/Sec/AmdSev.h
+++ b/OvmfPkg/Sec/AmdSev.h
@@ -91,4 +91,18 @@ SevSnpIsEnabled (
   VOID
   );
 
+/**
+  Map MMIO regions unencrypted if SEV-ES is active.
+
+  During early booting, page table entries default to having the encryption bit
+  set for SEV-ES/SEV-SNP guests. In cases where there is MMIO to an address, the
+  encryption bit should be cleared. Clear it here for any known MMIO accesses
+  during SEC, which is currently just the APIC base address.
+
+**/
+VOID
+SecMapApicBaseUnencrypted (
+  VOID
+  );
+
 #endif
diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c
index a30d4ce09e..60dfa61842 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -938,6 +938,7 @@ SecCoreStartupWithStack (
   // interrupts before initializing the Debug Agent and the debug timer is
   // enabled.
   //
+  SecMapApicBaseUnencrypted ();
   InitializeApicTimer (0, MAX_UINT32, TRUE, 5);
   DisableApicTimerInterrupt ();
 
diff --git a/OvmfPkg/Sec/SecMain.inf b/OvmfPkg/Sec/SecMain.inf
index dca932a474..88c2d3fb6d 100644
--- a/OvmfPkg/Sec/SecMain.inf
+++ b/OvmfPkg/Sec/SecMain.inf
@@ -55,6 +55,7 @@
   MemEncryptSevLib
   CpuExceptionHandlerLib
   CcProbeLib
+  CpuPageTableLib
 
 [Ppis]
   gEfiTemporaryRamSupportPpiGuid                # PPI ALWAYS_PRODUCED
@@ -83,6 +84,8 @@
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase
   gUefiOvmfPkgTokenSpaceGuid.PcdTdxAcceptPageSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecApicPageTableSize
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
-- 
2.25.1



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