[PATCH v5 27/42] OvmfPkg: Create a GHCB page for use during Sec phase


Lendacky, Thomas
 

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.

Two new fixed PCDs are needed to support the SEC GHCB page:
- PcdOvmfSecGhcbBase UINT64 value that is the base address of the
GHCB used during the SEC phase.
- PcdOvmfSecGhcbSize UINT64 value that is the size, in bytes, of the
GHCB area used during the SEC phase.

Cc: Jordan Justen <jordan.l.justen@...>
Cc: Laszlo Ersek <lersek@...>
Cc: Ard Biesheuvel <ard.biesheuvel@...>
Reviewed-by: Laszlo Ersek <lersek@...>
Signed-off-by: Tom Lendacky <thomas.lendacky@...>
---
OvmfPkg/OvmfPkg.dec | 9 +++
OvmfPkg/OvmfPkgX64.fdf | 6 ++
OvmfPkg/ResetVector/ResetVector.inf | 5 ++
OvmfPkg/ResetVector/Ia32/PageTables64.asm | 76 +++++++++++++++++++++++
OvmfPkg/ResetVector/ResetVector.nasmb | 17 +++++
5 files changed, 113 insertions(+)

diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
index 4c5b6511cb97..0e11913ee2e4 100644
--- a/OvmfPkg/OvmfPkg.dec
+++ b/OvmfPkg/OvmfPkg.dec
@@ -228,6 +228,15 @@ [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
+
+ ## The base address of the SEC GHCB page used by SEV-ES.
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase|0|UINT32|0x36
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize|0|UINT32|0x37
+
[PcdsDynamic, PcdsDynamicEx]
gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 0488e5d95ffe..39291f413f6d 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
+gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize
+
0x010000|0x010000
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize

diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/ResetVector.inf
index b0ddfa5832a2..483fd90fe785 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]
@@ -33,5 +34,9 @@ [BuildOptions]
*_*_X64_NASMB_FLAGS = -I$(WORKSPACE)/UefiCpuPkg/ResetVector/Vtf0/

[Pcd]
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase
+ gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableSize
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesSize
diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
index abad009f20f5..9f86ddf6f08f 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 + \
@@ -75,6 +80,37 @@ NoSev:
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
;
@@ -139,6 +175,46 @@ 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 75cfe16654b1..bfb77e439105 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -53,8 +53,25 @@
%error "This implementation inherently depends on PcdOvmfSecPageTablesSize"
%endif

+ %if (FixedPcdGet32 (PcdOvmfSecGhcbPageTableSize) != 0x1000)
+ %error "This implementation inherently depends on PcdOvmfSecGhcbPageTableSize"
+ %endif
+
+ %if (FixedPcdGet32 (PcdOvmfSecGhcbSize) != 0x2000)
+ %error "This implementation inherently depends on PcdOvmfSecGhcbSize"
+ %endif
+
+ %if ((FixedPcdGet32 (PcdOvmfSecGhcbBase) >> 21) != \
+ ((FixedPcdGet32 (PcdOvmfSecGhcbBase) + FixedPcdGet32 (PcdOvmfSecGhcbSize) - 1) >> 21))
+ %error "This implementation inherently depends on PcdOvmfSecGhcbBase 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 (PcdOvmfSecGhcbBase))
+ %define GHCB_SIZE (FixedPcdGet32 (PcdOvmfSecGhcbSize))
%include "Ia32/PageTables64.asm"
%endif

--
2.17.1

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