[RFC PATCH v3 26/43] OvmfPkg: Create a GHCB page for use during Sec phase

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

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

A GHCB page is needed during the Sec phase, so this new page must be
created. Since the #VC exception handler routines assume that a per-CPU
variable area is immediately after the GHCB, this per-CPU variable area
must also be created. Since the GHCB must be marked as an un-encrypted,
or shared, page, an additional pagetable page is required to break down
the 2MB region where the GHCB page lives into 4K pagetable entries.

Create a new entry in the OVMF memory layout for the new page table
page and for the SEC GHCB and per-CPU variable pages. After breaking down
the 2MB page, update the GHCB page table entry to remove the encryption
mask.

The GHCB page will be used by the SEC #VC exception handler. The #VC
exception handler will fill in the necessary fields of the GHCB and exit
to the hypervisor using the VMGEXIT instruction. The hypervisor then
accesses the GHCB in order to perform the requested function.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 OvmfPkg/OvmfPkg.dec                       |  5 ++
 OvmfPkg/OvmfPkgX64.fdf                    |  6 ++
 OvmfPkg/ResetVector/ResetVector.inf       |  5 ++
 OvmfPkg/ResetVector/Ia32/PageTables64.asm | 76 +++++++++++++++++++++++
 OvmfPkg/ResetVector/ResetVector.nasmb     | 16 +++++
 5 files changed, 108 insertions(+)

diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
index d5fee805ef4a..19723786d729 100644
--- a/OvmfPkg/OvmfPkg.dec
+++ b/OvmfPkg/OvmfPkg.dec
@@ -228,6 +228,11 @@ [PcdsFixedAtBuild]
   ## Number of page frames to use for storing grant table entries.
   gUefiOvmfPkgTokenSpaceGuid.PcdXenGrantFrames|4|UINT32|0x33
 
+  ## Specify the extra page table needed to mark the GHCB as unencrypted.
+  #  The value should be a multiple of 4KB for each.
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase|0x0|UINT32|0x34
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableSize|0x0|UINT32|0x35
+
 [PcdsDynamic, PcdsDynamicEx]
   gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index e49adc425fce..973b19fdbf19 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -76,6 +76,12 @@ [FD.MEMFD]
 0x007000|0x001000
 gEfiMdePkgTokenSpaceGuid.PcdGuidedExtractHandlerTableAddress|gUefiOvmfPkgTokenSpaceGuid.PcdGuidedExtractHandlerTableSize
 
+0x008000|0x001000
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableSize
+
+0x009000|0x002000
+gEfiMdeModulePkgTokenSpaceGuid.PcdSecGhcbBase|gEfiMdeModulePkgTokenSpaceGuid.PcdSecGhcbSize
+
 0x010000|0x010000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/ResetVector.inf
index 960b47cd0797..266c5fc5c8b3 100644
--- a/OvmfPkg/ResetVector/ResetVector.inf
+++ b/OvmfPkg/ResetVector/ResetVector.inf
@@ -26,6 +26,7 @@ [Sources]
 [Packages]
   OvmfPkg/OvmfPkg.dec
   MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
   UefiCpuPkg/UefiCpuPkg.dec
 
 [BuildOptions]
@@ -33,7 +34,11 @@ [BuildOptions]
    *_*_X64_NASMB_FLAGS = -I$(WORKSPACE)/UefiCpuPkg/ResetVector/Vtf0/
 
 [Pcd]
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSecGhcbBase
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSecGhcbSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableSize
diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
index c902fa68d556..b064ca65b88d 100644
--- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
+++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
@@ -21,6 +21,11 @@ BITS    32
 %define PAGE_2M_MBO            0x080
 %define PAGE_2M_PAT          0x01000
 
+%define PAGE_4K_PDE_ATTR (PAGE_ACCESSED + \
+                          PAGE_DIRTY + \
+                          PAGE_READ_WRITE + \
+                          PAGE_PRESENT)
+
 %define PAGE_2M_PDE_ATTR (PAGE_2M_MBO + \
                           PAGE_ACCESSED + \
                           PAGE_DIRTY + \
@@ -123,6 +128,37 @@ SevExit:
 
     OneTimeCallRet CheckSevFeature
 
+; Check if Secure Encrypted Virtualization - Encrypted State (SEV-ES) feature
+; is enabled.
+;
+; Modified:  EAX, EBX, ECX
+;
+; If SEV-ES is enabled then EAX will be non-zero.
+; If SEV-ES is disabled then EAX will be zero.
+;
+CheckSevEsFeature:
+    xor       eax, eax
+
+    ; SEV-ES can't be enabled if SEV isn't, so first check the encryption
+    ; mask.
+    test      edx, edx
+    jz        NoSevEs
+
+    ; Save current value of encryption mask
+    mov       ebx, edx
+
+    ; Check if SEV-ES is enabled
+    ;  MSR_0xC0010131 - Bit 1 (SEV-ES enabled)
+    mov       ecx, 0xc0010131
+    rdmsr
+    and       eax, 2
+
+    ; Restore encryption mask
+    mov       edx, ebx
+
+NoSevEs:
+    OneTimeCallRet CheckSevEsFeature
+
 ;
 ; Modified:  EAX, EBX, ECX, EDX
 ;
@@ -187,6 +223,46 @@ pageTableEntriesLoop:
     mov     [(ecx * 8 + PT_ADDR (0x2000 - 8)) + 4], edx
     loop    pageTableEntriesLoop
 
+    OneTimeCall   CheckSevEsFeature
+    test    eax, eax
+    jz      SetCr3
+
+    ;
+    ; 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.
+    ;
+    mov     ecx, (GHCB_BASE >> 21)
+    mov     eax, GHCB_PT_ADDR + PAGE_PDP_ATTR
+    mov     [ecx * 8 + PT_ADDR (0x2000)], eax
+
+    ;
+    ; Page Table Entries (512 * 4KB entries => 2MB)
+    ;
+    mov     ecx, 512
+pageTableEntries4kLoop:
+    mov     eax, ecx
+    dec     eax
+    shl     eax, 12
+    add     eax, GHCB_BASE & 0xFFE0_0000
+    add     eax, PAGE_4K_PDE_ATTR
+    mov     [ecx * 8 + GHCB_PT_ADDR - 8], eax
+    mov     [(ecx * 8 + GHCB_PT_ADDR - 8) + 4], edx
+    loop    pageTableEntries4kLoop
+
+    ;
+    ; Clear the encryption bit from the GHCB entry
+    ;
+    mov     ecx, (GHCB_BASE & 0x1F_FFFF) >> 12
+    mov     [ecx * 8 + GHCB_PT_ADDR + 4], strict dword 0
+
+    mov     ecx, GHCB_SIZE / 4
+    xor     eax, eax
+clearGhcbMemoryLoop:
+    mov     dword[ecx * 4 + GHCB_BASE - 4], eax
+    loop    clearGhcbMemoryLoop
+
+SetCr3:
     ;
     ; Set CR3 now that the paging structures are available
     ;
diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
index 579c75f5ba0c..708bbda6208f 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -53,9 +53,25 @@
     %error "This implementation inherently depends on PcdOvmfSecPageTablesSize"
   %endif
 
+  %if (FixedPcdGet32 (PcdOvmfSecGhcbPageTableSize) != 0x1000)
+    %error "This implementation inherently depends on PcdOvmfSecGhcbPageTableSize"
+  %endif
+
+  %if (FixedPcdGet32 (PcdSecGhcbSize) != 0x2000)
+    %error "This implementation inherently depends on PcdSecGhcbSize"
+  %endif
+
+  %if ((FixedPcdGet32 (PcdSecGhcbBase) >> 21) != \
+       ((FixedPcdGet32 (PcdSecGhcbBase) + FixedPcdGet32 (PcdSecGhcbSize) - 1) >> 21))
+    %error "This implementation inherently depends on PcdSecGhcbBase not straddling a 2MB boundary"
+  %endif
+
   %define PT_ADDR(Offset) (FixedPcdGet32 (PcdOvmfSecPageTablesBase) + (Offset))
 %include "Ia32/Flat32ToFlat64.asm"
 
+  %define GHCB_PT_ADDR (FixedPcdGet32 (PcdOvmfSecGhcbPageTableBase))
+  %define GHCB_BASE (FixedPcdGet32 (PcdSecGhcbBase))
+  %define GHCB_SIZE (FixedPcdGet32 (PcdSecGhcbSize))
   %define SEV_ES_VC_TOP_OF_STACK (FixedPcdGet32 (PcdOvmfSecPeiTempRamBase) + FixedPcdGet32 (PcdOvmfSecPeiTempRamSize))
 %include "Ia32/PageTables64.asm"
 %endif
-- 
2.17.1