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audk/OvmfPkg/ResetVector/Ia32/AmdSev.asm

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NASM
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;------------------------------------------------------------------------------
; @file
; Provide the functions to check whether SEV and SEV-ES is enabled.
;
; Copyright (c) 2017 - 2021, Advanced Micro Devices, Inc. All rights reserved.<BR>
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
;------------------------------------------------------------------------------
BITS 32
;
; SEV-ES #VC exception handler support
;
; #VC handler local variable locations
;
%define VC_CPUID_RESULT_EAX 0
%define VC_CPUID_RESULT_EBX 4
%define VC_CPUID_RESULT_ECX 8
%define VC_CPUID_RESULT_EDX 12
%define VC_GHCB_MSR_EDX 16
%define VC_GHCB_MSR_EAX 20
%define VC_CPUID_REQUEST_REGISTER 24
%define VC_CPUID_FUNCTION 28
; #VC handler total local variable size
;
%define VC_VARIABLE_SIZE 32
; #VC handler GHCB CPUID request/response protocol values
;
%define GHCB_CPUID_REQUEST 4
%define GHCB_CPUID_RESPONSE 5
%define GHCB_CPUID_REGISTER_SHIFT 30
%define CPUID_INSN_LEN 2
; #VC handler offsets/sizes for accessing SNP CPUID page
;
%define SNP_CPUID_ENTRY_SZ 48
%define SNP_CPUID_COUNT 0
%define SNP_CPUID_ENTRY 16
%define SNP_CPUID_ENTRY_EAX_IN 0
%define SNP_CPUID_ENTRY_ECX_IN 4
%define SNP_CPUID_ENTRY_EAX 24
%define SNP_CPUID_ENTRY_EBX 28
%define SNP_CPUID_ENTRY_ECX 32
%define SNP_CPUID_ENTRY_EDX 36
%define SEV_GHCB_MSR 0xc0010130
%define SEV_STATUS_MSR 0xc0010131
; The #VC was not for CPUID
%define TERM_VC_NOT_CPUID 1
; The unexpected response code
%define TERM_UNEXPECTED_RESP_CODE 2
%define PAGE_PRESENT 0x01
%define PAGE_READ_WRITE 0x02
%define PAGE_USER_SUPERVISOR 0x04
%define PAGE_WRITE_THROUGH 0x08
%define PAGE_CACHE_DISABLE 0x010
%define PAGE_ACCESSED 0x020
%define PAGE_DIRTY 0x040
%define PAGE_PAT 0x080
%define PAGE_GLOBAL 0x0100
%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_PDP_ATTR (PAGE_ACCESSED + \
PAGE_READ_WRITE + \
PAGE_PRESENT)
; Macro is used to issue the MSR protocol based VMGEXIT. The caller is
; responsible to populate values in the EDX:EAX registers. After the vmmcall
; returns, it verifies that the response code matches with the expected
; code. If it does not match then terminate the guest. The result of request
; is returned in the EDX:EAX.
;
; args 1:Request code, 2: Response code
%macro VmgExit 2
;
; Add request code:
; GHCB_MSR[11:0] = Request code
or eax, %1
mov ecx, SEV_GHCB_MSR
wrmsr
; Issue VMGEXIT - NASM doesn't support the vmmcall instruction in 32-bit
; mode, so work around this by temporarily switching to 64-bit mode.
;
BITS 64
rep vmmcall
BITS 32
mov ecx, SEV_GHCB_MSR
rdmsr
;
; Verify the reponse code, if it does not match then request to terminate
; GHCB_MSR[11:0] = Response code
mov ecx, eax
and ecx, 0xfff
cmp ecx, %2
jne SevEsUnexpectedRespTerminate
%endmacro
; Macro to terminate the guest using the VMGEXIT.
; arg 1: reason code
%macro TerminateVmgExit 1
mov eax, %1
;
; Use VMGEXIT to request termination. At this point the reason code is
; located in EAX, so shift it left 16 bits to the proper location.
;
; EAX[11:0] => 0x100 - request termination
; EAX[15:12] => 0x1 - OVMF
; EAX[23:16] => 0xXX - REASON CODE
;
shl eax, 16
or eax, 0x1100
xor edx, edx
mov ecx, SEV_GHCB_MSR
wrmsr
;
; Issue VMGEXIT - NASM doesn't support the vmmcall instruction in 32-bit
; mode, so work around this by temporarily switching to 64-bit mode.
;
BITS 64
rep vmmcall
BITS 32
;
; We shouldn't come back from the VMGEXIT, but if we do, just loop.
;
%%TerminateHlt:
hlt
jmp %%TerminateHlt
%endmacro
; Terminate the guest due to unexpected response code.
SevEsUnexpectedRespTerminate:
TerminateVmgExit TERM_UNEXPECTED_RESP_CODE
%ifdef ARCH_X64
; If SEV-ES is enabled then initialize and make the GHCB page shared
SevClearPageEncMaskForGhcbPage:
; Check if SEV is enabled
cmp byte[WORK_AREA_GUEST_TYPE], 1
jnz SevClearPageEncMaskForGhcbPageExit
; Check if SEV-ES is enabled
mov ecx, 1
bt [SEV_ES_WORK_AREA_STATUS_MSR], ecx
jnc SevClearPageEncMaskForGhcbPageExit
;
; 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
SevClearPageEncMaskForGhcbPageExit:
OneTimeCallRet SevClearPageEncMaskForGhcbPage
; Check if SEV is enabled, and get the C-bit mask above 31.
; Modified: EDX
;
; The value is returned in the EDX
GetSevCBitMaskAbove31:
xor edx, edx
; Check if SEV is enabled
cmp byte[WORK_AREA_GUEST_TYPE], 1
jnz GetSevCBitMaskAbove31Exit
mov edx, dword[SEV_ES_WORK_AREA_ENC_MASK + 4]
GetSevCBitMaskAbove31Exit:
OneTimeCallRet GetSevCBitMaskAbove31
%endif
; Check if Secure Encrypted Virtualization (SEV) features are enabled.
;
; Register usage is tight in this routine, so multiple calls for the
; same CPUID and MSR data are performed to keep things simple.
;
; Modified: EAX, EBX, ECX, EDX, ESP
;
; If SEV is enabled then EAX will be at least 32.
; If SEV is disabled then EAX will be zero.
;
CheckSevFeatures:
;
; Clear the workarea, if SEV is enabled then later part of routine
; will populate the workarea fields.
;
mov ecx, SEV_ES_WORK_AREA_SIZE
mov eax, SEV_ES_WORK_AREA
ClearSevEsWorkArea:
mov byte [eax], 0
inc eax
loop ClearSevEsWorkArea
;
; Set up exception handlers to check for SEV-ES
; Load temporary RAM stack based on PCDs (see SevEsIdtVmmComm for
; stack usage)
; Establish exception handlers
;
mov esp, SEV_ES_VC_TOP_OF_STACK
mov eax, ADDR_OF(Idtr)
lidt [cs:eax]
; Check if we have a valid (0x8000_001F) CPUID leaf
; CPUID raises a #VC exception if running as an SEV-ES guest
mov eax, 0x80000000
cpuid
; This check should fail on Intel or Non SEV AMD CPUs. In future if
; Intel CPUs supports this CPUID leaf then we are guranteed to have exact
; same bit definition.
cmp eax, 0x8000001f
jl NoSev
; Check for SEV memory encryption feature:
; CPUID Fn8000_001F[EAX] - Bit 1
; CPUID raises a #VC exception if running as an SEV-ES guest
mov eax, 0x8000001f
cpuid
bt eax, 1
jnc NoSev
; Check if SEV memory encryption is enabled
; MSR_0xC0010131 - Bit 0 (SEV enabled)
mov ecx, SEV_STATUS_MSR
rdmsr
bt eax, 0
jnc NoSev
; Set the work area header to indicate that the SEV is enabled
mov byte[WORK_AREA_GUEST_TYPE], 1
; Save the SevStatus MSR value in the workarea
mov [SEV_ES_WORK_AREA_STATUS_MSR], eax
mov [SEV_ES_WORK_AREA_STATUS_MSR + 4], edx
; Check if SEV-ES is enabled
; MSR_0xC0010131 - Bit 1 (SEV-ES enabled)
mov ecx, SEV_STATUS_MSR
rdmsr
bt eax, 1
jnc GetSevEncBit
GetSevEncBit:
; Get pte bit position to enable memory encryption
; CPUID Fn8000_001F[EBX] - Bits 5:0
;
and ebx, 0x3f
mov eax, ebx
; The encryption bit position is always above 31
sub ebx, 32
jns SevSaveMask
; Encryption bit was reported as 31 or below, enter a HLT loop
SevEncBitLowHlt:
cli
hlt
jmp SevEncBitLowHlt
SevSaveMask:
xor edx, edx
bts edx, ebx
mov dword[SEV_ES_WORK_AREA_ENC_MASK], 0
mov dword[SEV_ES_WORK_AREA_ENC_MASK + 4], edx
jmp SevExit
NoSev:
;
; Perform an SEV-ES sanity check by seeing if a #VC exception occurred.
;
; If SEV-ES is enabled, the CPUID instruction will trigger a #VC exception
; where the RECEIVED_VC offset in the workarea will be set to one.
;
cmp byte[SEV_ES_WORK_AREA_RECEIVED_VC], 0
jz NoSevPass
;
; A #VC was received, yet CPUID indicates no SEV-ES support, something
; isn't right.
;
NoSevEsVcHlt:
cli
hlt
jmp NoSevEsVcHlt
NoSevPass:
xor eax, eax
SevExit:
;
; Clear exception handlers and stack
;
push eax
mov eax, ADDR_OF(IdtrClear)
lidt [cs:eax]
pop eax
mov esp, 0
OneTimeCallRet CheckSevFeatures
; Start of #VC exception handling routines
;
SevEsIdtNotCpuid:
TerminateVmgExit TERM_VC_NOT_CPUID
iret
; Use the SNP CPUID page to handle the cpuid lookup
;
; Modified: EAX, EBX, ECX, EDX
;
; Relies on the stack setup/usage in #VC handler:
;
; On entry,
; [esp + VC_CPUID_FUNCTION] contains EAX input to cpuid instruction
;
; On return, stores corresponding results of CPUID lookup in:
; [esp + VC_CPUID_RESULT_EAX]
; [esp + VC_CPUID_RESULT_EBX]
; [esp + VC_CPUID_RESULT_ECX]
; [esp + VC_CPUID_RESULT_EDX]
;
SnpCpuidLookup:
mov eax, [esp + VC_CPUID_FUNCTION]
mov ebx, [CPUID_BASE + SNP_CPUID_COUNT]
mov ecx, CPUID_BASE + SNP_CPUID_ENTRY
; Zero these out now so we can simply return if lookup fails
mov dword[esp + VC_CPUID_RESULT_EAX], 0
mov dword[esp + VC_CPUID_RESULT_EBX], 0
mov dword[esp + VC_CPUID_RESULT_ECX], 0
mov dword[esp + VC_CPUID_RESULT_EDX], 0
SnpCpuidCheckEntry:
cmp ebx, 0
je VmmDoneSnpCpuid
cmp dword[ecx + SNP_CPUID_ENTRY_EAX_IN], eax
jne SnpCpuidCheckEntryNext
; As with SEV-ES handler we assume requested CPUID sub-leaf/index is 0
cmp dword[ecx + SNP_CPUID_ENTRY_ECX_IN], 0
je SnpCpuidEntryFound
SnpCpuidCheckEntryNext:
dec ebx
add ecx, SNP_CPUID_ENTRY_SZ
jmp SnpCpuidCheckEntry
SnpCpuidEntryFound:
mov eax, [ecx + SNP_CPUID_ENTRY_EAX]
mov [esp + VC_CPUID_RESULT_EAX], eax
mov eax, [ecx + SNP_CPUID_ENTRY_EBX]
mov [esp + VC_CPUID_RESULT_EBX], eax
mov eax, [ecx + SNP_CPUID_ENTRY_EDX]
mov [esp + VC_CPUID_RESULT_ECX], eax
mov eax, [ecx + SNP_CPUID_ENTRY_ECX]
mov [esp + VC_CPUID_RESULT_EDX], eax
jmp VmmDoneSnpCpuid
;
; Total stack usage for the #VC handler is 44 bytes:
; - 12 bytes for the exception IRET (after popping error code)
; - 32 bytes for the local variables.
;
SevEsIdtVmmComm:
;
; If we're here, then we are an SEV-ES guest and this
; was triggered by a CPUID instruction
;
; Set the recievedVc field in the workarea to communicate that
; a #VC was taken.
mov byte[SEV_ES_WORK_AREA_RECEIVED_VC], 1
pop ecx ; Error code
cmp ecx, 0x72 ; Be sure it was CPUID
jne SevEsIdtNotCpuid
; Set up local variable room on the stack
; CPUID function : + 28
; CPUID request register : + 24
; GHCB MSR (EAX) : + 20
; GHCB MSR (EDX) : + 16
; CPUID result (EDX) : + 12
; CPUID result (ECX) : + 8
; CPUID result (EBX) : + 4
; CPUID result (EAX) : + 0
sub esp, VC_VARIABLE_SIZE
; Save the CPUID function being requested
mov [esp + VC_CPUID_FUNCTION], eax
; If SEV-SNP is enabled, use the CPUID page to handle the CPUID
; instruction.
mov ecx, SEV_STATUS_MSR
rdmsr
bt eax, 2
jc SnpCpuidLookup
; The GHCB CPUID protocol uses the following mapping to request
; a specific register:
; 0 => EAX, 1 => EBX, 2 => ECX, 3 => EDX
;
; Set EAX as the first register to request. This will also be used as a
; loop variable to request all register values (EAX to EDX).
xor eax, eax
mov [esp + VC_CPUID_REQUEST_REGISTER], eax
; Save current GHCB MSR value
mov ecx, SEV_GHCB_MSR
rdmsr
mov [esp + VC_GHCB_MSR_EAX], eax
mov [esp + VC_GHCB_MSR_EDX], edx
NextReg:
;
; Setup GHCB MSR
; GHCB_MSR[63:32] = CPUID function
; GHCB_MSR[31:30] = CPUID register
; GHCB_MSR[11:0] = CPUID request protocol
;
mov eax, [esp + VC_CPUID_REQUEST_REGISTER]
cmp eax, 4
jge VmmDone
shl eax, GHCB_CPUID_REGISTER_SHIFT
mov edx, [esp + VC_CPUID_FUNCTION]
VmgExit GHCB_CPUID_REQUEST, GHCB_CPUID_RESPONSE
;
; Response GHCB MSR
; GHCB_MSR[63:32] = CPUID register value
; GHCB_MSR[31:30] = CPUID register
; GHCB_MSR[11:0] = CPUID response protocol
;
; Save returned value
shr eax, GHCB_CPUID_REGISTER_SHIFT
mov [esp + eax * 4], edx
; Next register
inc word [esp + VC_CPUID_REQUEST_REGISTER]
jmp NextReg
VmmDone:
;
; At this point we have all CPUID register values. Restore the GHCB MSR,
; set the return register values and return.
;
mov eax, [esp + VC_GHCB_MSR_EAX]
mov edx, [esp + VC_GHCB_MSR_EDX]
mov ecx, SEV_GHCB_MSR
wrmsr
VmmDoneSnpCpuid:
mov eax, [esp + VC_CPUID_RESULT_EAX]
mov ebx, [esp + VC_CPUID_RESULT_EBX]
mov ecx, [esp + VC_CPUID_RESULT_ECX]
mov edx, [esp + VC_CPUID_RESULT_EDX]
add esp, VC_VARIABLE_SIZE
; Update the EIP value to skip over the now handled CPUID instruction
; (the CPUID instruction has a length of 2)
add word [esp], CPUID_INSN_LEN
iret
ALIGN 2
Idtr:
dw IDT_END - IDT_BASE - 1 ; Limit
dd ADDR_OF(IDT_BASE) ; Base
IdtrClear:
dw 0 ; Limit
dd 0 ; Base
ALIGN 16
;
; The Interrupt Descriptor Table (IDT)
; This will be used to determine if SEV-ES is enabled. Upon execution
; of the CPUID instruction, a VMM Communication Exception will occur.
; This will tell us if SEV-ES is enabled. We can use the current value
; of the GHCB MSR to determine the SEV attributes.
;
IDT_BASE:
;
; Vectors 0 - 28 (No handlers)
;
%rep 29
dw 0 ; Offset low bits 15..0
dw 0x10 ; Selector
db 0 ; Reserved
db 0x8E ; Gate Type (IA32_IDT_GATE_TYPE_INTERRUPT_32)
dw 0 ; Offset high bits 31..16
%endrep
;
; Vector 29 (VMM Communication Exception)
;
dw (ADDR_OF(SevEsIdtVmmComm) & 0xffff) ; Offset low bits 15..0
dw 0x10 ; Selector
db 0 ; Reserved
db 0x8E ; Gate Type (IA32_IDT_GATE_TYPE_INTERRUPT_32)
dw (ADDR_OF(SevEsIdtVmmComm) >> 16) ; Offset high bits 31..16
;
; Vectors 30 - 31 (No handlers)
;
%rep 2
dw 0 ; Offset low bits 15..0
dw 0x10 ; Selector
db 0 ; Reserved
db 0x8E ; Gate Type (IA32_IDT_GATE_TYPE_INTERRUPT_32)
dw 0 ; Offset high bits 31..16
%endrep
IDT_END:
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