;/** @file
; Low level x64 routines used by the debug support driver.
;
; Copyright (c) 2007 - 2016, Intel Corporation. All rights reserved.<BR>
; This program and the accompanying materials
; are licensed and made available under the terms and conditions of the BSD License
; which accompanies this distribution. The full text of the license may be found at
; http://opensource.org/licenses/bsd-license.php
;
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
;
;**/
%define EXCPT64_DIVIDE_ERROR 0
%define EXCPT64_DEBUG 1
%define EXCPT64_NMI 2
%define EXCPT64_BREAKPOINT 3
%define EXCPT64_OVERFLOW 4
%define EXCPT64_BOUND 5
%define EXCPT64_INVALID_OPCODE 6
%define EXCPT64_DOUBLE_FAULT 8
%define EXCPT64_INVALID_TSS 10
%define EXCPT64_SEG_NOT_PRESENT 11
%define EXCPT64_STACK_FAULT 12
%define EXCPT64_GP_FAULT 13
%define EXCPT64_PAGE_FAULT 14
%define EXCPT64_FP_ERROR 16
%define EXCPT64_ALIGNMENT_CHECK 17
%define EXCPT64_MACHINE_CHECK 18
%define EXCPT64_SIMD 19
%define FXSTOR_FLAG 0x1000000 ; bit cpuid 24 of feature flags
;; The FXSTOR and FXRSTOR commands are used for saving and restoring the x87,
;; MMX, SSE, SSE2, etc registers. The initialization of the debugsupport driver
;; MUST check the CPUID feature flags to see that these instructions are available
;; and fail to init if they are not.
;; fxstor [rdi]
%macro FXSTOR_RDI 0
db 0xf, 0xae, 00000111y ; mod = 00, reg/op = 000, r/m = 111 = [rdi]
%endmacro
;; fxrstor [rsi]
%macro FXRSTOR_RSI 0
db 0xf, 0xae, 00001110y ; mod = 00, reg/op = 001, r/m = 110 = [rsi]
%endmacro
SECTION .data
global ASM_PFX(OrigVector)
global ASM_PFX(InterruptEntryStub)
global ASM_PFX(StubSize)
global ASM_PFX(CommonIdtEntry)
global ASM_PFX(FxStorSupport)
extern ASM_PFX(InterruptDistrubutionHub)
ASM_PFX(StubSize): dd InterruptEntryStubEnd - ASM_PFX(InterruptEntryStub)
AppRsp: dq 0x1111111111111111 ; ?
DebugRsp: dq 0x2222222222222222 ; ?
ExtraPush: dq 0x3333333333333333 ; ?
ExceptData: dq 0x4444444444444444 ; ?
Rflags: dq 0x5555555555555555 ; ?
ASM_PFX(OrigVector): dq 0x6666666666666666 ; ?
;; The declarations below define the memory region that will be used for the debug stack.
;; The context record will be built by pushing register values onto this stack.
;; It is imparitive that alignment be carefully managed, since the FXSTOR and
;; FXRSTOR instructions will GP fault if their memory operand is not 16 byte aligned.
;;
;; The stub will switch stacks from the application stack to the debuger stack
;; and pushes the exception number.
;;
;; Then we building the context record on the stack. Since the stack grows down,
;; we push the fields of the context record from the back to the front. There
;; are 336 bytes of stack used prior allocating the 512 bytes of stack to be
;; used as the memory buffer for the fxstor instruction. Therefore address of
;; the buffer used for the FXSTOR instruction is &Eax - 336 - 512, which
;; must be 16 byte aligned.
;;
;; We carefully locate the stack to make this happen.
;;
;; For reference, the context structure looks like this:
;; struct {
;; UINT64 ExceptionData;
;; FX_SAVE_STATE_X64 FxSaveState; // 512 bytes, must be 16 byte aligned
;; UINT64 Dr0, Dr1, Dr2, Dr3, Dr6, Dr7;
;; UINT64 Cr0, Cr1, Cr2, Cr3, Cr4, Cr8;
;; UINT64 RFlags;
;; UINT64 Ldtr, Tr;
;; UINT64 Gdtr[2], Idtr[2];
;; UINT64 Rip;
;; UINT64 Gs, Fs, Es, Ds, Cs, Ss;
;; UINT64 Rdi, Rsi, Rbp, Rsp, Rbx, Rdx, Rcx, Rax;
;; UINT64 R8, R9, R10, R11, R12, R13, R14, R15;
;; } SYSTEM_CONTEXT_X64; // 64 bit system context record
align 16
DebugStackEnd: db "DbgStkEnd >>>>>>" ;; 16 byte long string - must be 16 bytes to preserve alignment
times 0x1ffc dd 0x0 ;; 32K should be enough stack
;; This allocation is coocked to insure
;; that the the buffer for the FXSTORE instruction
;; will be 16 byte aligned also.
;;
ExceptionNumber: dq 0 ;; first entry will be the vector number pushed by the stub
DebugStackBegin: db "<<<< DbgStkBegin" ;; initial debug ESP == DebugStackBegin, set in stub
DEFAULT REL
SECTION .text
;------------------------------------------------------------------------------
; BOOLEAN
; FxStorSupport (
; void
; )
;
; Abstract: Returns TRUE if FxStor instructions are supported
;
global ASM_PFX(FxStorSupport)
ASM_PFX(FxStorSupport):
;
; cpuid corrupts rbx which must be preserved per the C calling convention
;
push rbx
mov rax, dword 1
cpuid
mov eax, edx
and rax, FXSTOR_FLAG
shr rax, 24
pop rbx
ret
;------------------------------------------------------------------------------
; void
; Vect2Desc (
; IA32_IDT_GATE_DESCRIPTOR * DestDesc, // rcx
; void (*Vector) (void) // rdx
; )
;
; Abstract: Encodes an IDT descriptor with the given physical address
;
global ASM_PFX(Vect2Desc)
ASM_PFX(Vect2Desc):
mov rax, rdx
mov word [rcx], ax ; write bits 15..0 of offset
mov dx, cs
mov word [rcx+2], dx ; SYS_CODE_SEL from GDT
mov word [rcx+4], 0xe00 | 0x8000 ; type = 386 interrupt gate, present
shr rax, 16
mov word [rcx+6], ax ; write bits 31..16 of offset
shr rax, 16
mov dword [rcx+8], eax ; write bits 63..32 of offset
ret
;------------------------------------------------------------------------------
; InterruptEntryStub
;
; Abstract: This code is not a function, but is a small piece of code that is
; copied and fixed up once for each IDT entry that is hooked.
;
ASM_PFX(InterruptEntryStub):
push 0 ; push vector number - will be modified before installed
db 0xe9 ; jump rel32
dd 0 ; fixed up to relative address of CommonIdtEntry
InterruptEntryStubEnd:
;------------------------------------------------------------------------------
; CommonIdtEntry
;
; Abstract: This code is not a function, but is the common part for all IDT
; vectors.
;
ASM_PFX(CommonIdtEntry):
;;
;; At this point, the stub has saved the current application stack esp into AppRsp
;; and switched stacks to the debug stack, where it pushed the vector number
;;
;; The application stack looks like this:
;;
;; ...
;; (last application stack entry)
;; [16 bytes alignment, do not care it]
;; SS from interrupted task
;; RSP from interrupted task
;; rflags from interrupted task
;; CS from interrupted task
;; RIP from interrupted task
;; Error code <-------------------- Only present for some exeption types
;;
;; Vector Number <----------------- pushed in our IDT Entry
;;
;; The stub switched us to the debug stack and pushed the interrupt number.
;;
;; Next, construct the context record. It will be build on the debug stack by
;; pushing the registers in the correct order so as to create the context structure
;; on the debug stack. The context record must be built from the end back to the
;; beginning because the stack grows down...
;
;; For reference, the context record looks like this:
;;
;; typedef
;; struct {
;; UINT64 ExceptionData;
;; FX_SAVE_STATE_X64 FxSaveState;
;; UINT64 Dr0, Dr1, Dr2, Dr3, Dr6, Dr7;
;; UINT64 Cr0, Cr2, Cr3, Cr4, Cr8;
;; UINT64 RFlags;
;; UINT64 Ldtr, Tr;
;; UINT64 Gdtr[2], Idtr[2];
;; UINT64 Rip;
;; UINT64 Gs, Fs, Es, Ds, Cs, Ss;
;; UINT64 Rdi, Rsi, Rbp, Rsp, Rbx, Rdx, Rcx, Rax;
;; UINT64 R8, R9, R10, R11, R12, R13, R14, R15;
;; } SYSTEM_CONTEXT_X64; // 64 bit system context record
;; NOTE: we save rsp here to prevent compiler put rip reference cause error AppRsp
push rax
mov rax, qword [rsp+8] ; save vector number
mov [ExceptionNumber], rax ; save vector number
pop rax
add rsp, 8 ; pop vector number
mov [AppRsp], rsp ; save stack top
mov rsp, DebugStackBegin ; switch to debugger stack
sub rsp, 8 ; leave space for vector number
;; UINT64 Rdi, Rsi, Rbp, Rsp, Rbx, Rdx, Rcx, Rax;
;; UINT64 R8, R9, R10, R11, R12, R13, R14, R15;
push r15
push r14
push r13
push r12
push r11
push r10
push r9
push r8
push rax
push rcx
push rdx
push rbx
push rsp
push rbp
push rsi
push rdi
;; Save interrupt state rflags register...
pushfq
pop rax
mov [Rflags], rax
;; We need to determine if any extra data was pushed by the exception, and if so, save it
;; To do this, we check the exception number pushed by the stub, and cache the
;; result in a variable since we'll need this again.
cmp qword [ExceptionNumber], EXCPT64_DOUBLE_FAULT
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_INVALID_TSS
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_SEG_NOT_PRESENT
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_STACK_FAULT
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_GP_FAULT
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_PAGE_FAULT
jz ExtraPushOne
cmp qword [ExceptionNumber], EXCPT64_ALIGNMENT_CHECK
jz ExtraPushOne
mov qword [ExtraPush], 0
mov qword [ExceptData], 0
jmp ExtraPushDone
ExtraPushOne:
mov qword [ExtraPush], 1
;; If there's some extra data, save it also, and modify the saved AppRsp to effectively
;; pop this value off the application's stack.
mov rax, [AppRsp]
mov rbx, [rax]
mov qword [ExceptData], rbx
add rax, 8
mov [AppRsp], rax
ExtraPushDone:
;; The "push" above pushed the debug stack rsp. Since what we're actually doing
;; is building the context record on the debug stack, we need to save the pushed
;; debug RSP, and replace it with the application's last stack entry...
mov rax, [rsp + 24]
mov [DebugRsp], rax
mov rax, [AppRsp]
mov rax, QWORD [rax + 24]
; application stack has ss, rsp, rflags, cs, & rip, so
; last actual application stack entry is saved at offset
; 24 bytes from stack top.
mov [rsp + 24], rax
;; continue building context record
;; UINT64 Gs, Fs, Es, Ds, Cs, Ss; insure high 16 bits of each is zero
mov rax, ss
push rax
; CS from application is one entry back in application stack
mov rax, [AppRsp]
movzx rax, word [rax + 8]
push rax
mov rax, ds
push rax
mov rax, es
push rax
mov rax, fs
push rax
mov rax, gs
push rax
;; UINT64 Rip;
; Rip from application is on top of application stack
mov rax, [AppRsp]
push qword [rax]
;; UINT64 Gdtr[2], Idtr[2];
push 0
push 0
sidt [rsp]
push 0
push 0
sgdt [rsp]
;; UINT64 Ldtr, Tr;
xor rax, rax
str ax
push rax
sldt ax
push rax
;; UINT64 RFlags;
;; Rflags from application is two entries back in application stack
mov rax, [AppRsp]
push qword [rax + 16]
;; UINT64 Cr0, Cr1, Cr2, Cr3, Cr4, Cr8;
;; insure FXSAVE/FXRSTOR is enabled in CR4...
;; ... while we're at it, make sure DE is also enabled...
mov rax, cr8
push rax
mov rax, cr4
or rax, 0x208
mov cr4, rax
push rax
mov rax, cr3
push rax
mov rax, cr2
push rax
push 0
mov rax, cr0
push rax
;; UINT64 Dr0, Dr1, Dr2, Dr3, Dr6, Dr7;
mov rax, dr7
push rax
;; clear Dr7 while executing debugger itself
xor rax, rax
mov dr7, rax
mov rax, dr6
push rax
;; insure all status bits in dr6 are clear...
xor rax, rax
mov dr6, rax
mov rax, dr3
push rax
mov rax, dr2
push rax
mov rax, dr1
push rax
mov rax, dr0
push rax
;; FX_SAVE_STATE_X64 FxSaveState;
sub rsp, 512
mov rdi, rsp
; IMPORTANT!! The debug stack has been carefully constructed to
; insure that rsp and rdi are 16 byte aligned when we get here.
; They MUST be. If they are not, a GP fault will occur.
FXSTOR_RDI
;; UEFI calling convention for x64 requires that Direction flag in EFLAGs is clear
cld
;; UINT64 ExceptionData;
mov rax, [ExceptData]
push rax
; call to C code which will in turn call registered handler
; pass in the vector number
mov rdx, rsp
mov rcx, [ExceptionNumber]
sub rsp, 40
call ASM_PFX(InterruptDistrubutionHub)
add rsp, 40
; restore context...
;; UINT64 ExceptionData;
add rsp, 8
;; FX_SAVE_STATE_X64 FxSaveState;
mov rsi, rsp
FXRSTOR_RSI
add rsp, 512
;; UINT64 Dr0, Dr1, Dr2, Dr3, Dr6, Dr7;
pop rax
mov dr0, rax
pop rax
mov dr1, rax
pop rax
mov dr2, rax
pop rax
mov dr3, rax
;; skip restore of dr6. We cleared dr6 during the context save.
add rsp, 8
pop rax
mov dr7, rax
;; UINT64 Cr0, Cr1, Cr2, Cr3, Cr4, Cr8;
pop rax
mov cr0, rax
add rsp, 8
pop rax
mov cr2, rax
pop rax
mov cr3, rax
pop rax
mov cr4, rax
pop rax
mov cr8, rax
;; UINT64 RFlags;
mov rax, [AppRsp]
pop qword [rax + 16]
;; UINT64 Ldtr, Tr;
;; UINT64 Gdtr[2], Idtr[2];
;; Best not let anyone mess with these particular registers...
add rsp, 48
;; UINT64 Rip;
pop qword [rax]
;; UINT64 Gs, Fs, Es, Ds, Cs, Ss;
;; NOTE - modified segment registers could hang the debugger... We
;; could attempt to insulate ourselves against this possibility,
;; but that poses risks as well.
;;
pop rax
; mov gs, rax
pop rax
; mov fs, rax
pop rax
mov es, rax
pop rax
mov ds, rax
mov rax, [AppRsp]
pop qword [rax + 8]
pop rax
mov ss, rax
;; The next stuff to restore is the general purpose registers that were pushed
;; using the "push" instruction.
;;
;; The value of RSP as stored in the context record is the application RSP
;; including the 5 entries on the application stack caused by the exception
;; itself. It may have been modified by the debug agent, so we need to
;; determine if we need to relocate the application stack.
mov rbx, [rsp + 24] ; move the potentially modified AppRsp into rbx
mov rax, [AppRsp]
mov rax, QWORD [rax + 24]
cmp rbx, rax
je NoAppStackMove
mov rax, [AppRsp]
mov rcx, [rax] ; RIP
mov [rbx], rcx
mov rcx, [rax + 8] ; CS
mov [rbx + 8], rcx
mov rcx, [rax + 16] ; RFLAGS
mov [rbx + 16], rcx
mov rcx, [rax + 24] ; RSP
mov [rbx + 24], rcx
mov rcx, [rax + 32] ; SS
mov [rbx + 32], rcx
mov rax, rbx ; modify the saved AppRsp to the new AppRsp
mov [AppRsp], rax
NoAppStackMove:
mov rax, [DebugRsp] ; restore the DebugRsp on the debug stack
; so our "pop" will not cause a stack switch
mov [rsp + 24], rax
cmp qword [ExceptionNumber], 0x68
jne NoChain
Chain:
;; Restore rflags so when we chain, the flags will be exactly as if we were never here.
;; We gin up the stack to do an iretq so we can get ALL the flags.
mov rax, [AppRsp]
mov rbx, [rax + 40]
push rbx
mov rax, ss
push rax
mov rax, rsp
add rax, 16
push rax
mov rax, [AppRsp]
mov rbx, [rax + 16]
and rbx, ~ 0x300 ; special handling for IF and TF
push rbx
mov rax, cs
push rax
mov rax, PhonyIretq
push rax
iretq
PhonyIretq:
;; UINT64 Rdi, Rsi, Rbp, Rsp, Rbx, Rdx, Rcx, Rax;
;; UINT64 R8, R9, R10, R11, R12, R13, R14, R15;
pop rdi
pop rsi
pop rbp
pop rsp
pop rbx
pop rdx
pop rcx
pop rax
pop r8
pop r9
pop r10
pop r11
pop r12
pop r13
pop r14
pop r15
;; Switch back to application stack
mov rsp, [AppRsp]
;; Jump to original handler
jmp [ASM_PFX(OrigVector)]
NoChain:
;; UINT64 Rdi, Rsi, Rbp, Rsp, Rbx, Rdx, Rcx, Rax;
;; UINT64 R8, R9, R10, R11, R12, R13, R14, R15;
pop rdi
pop rsi
pop rbp
pop rsp
pop rbx
pop rdx
pop rcx
pop rax
pop r8
pop r9
pop r10
pop r11
pop r12
pop r13
pop r14
pop r15
;; Switch back to application stack
mov rsp, [AppRsp]
;; We're outa here...
iretq