summaryrefslogtreecommitdiff
path: root/MdePkg/Library/BaseLib/X64/Thunk16.asm
blob: 2ee40c2fe4704c30efffa4cf925c7adb9184cf67 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287

#include "BaseLibInternals.h"

;------------------------------------------------------------------------------
;
; Copyright (c) 2006, Intel Corporation
; All rights reserved. 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.
;
; Module Name:
;
;   Thunk.asm
;
; Abstract:
;
;   Real mode thunk
;
;------------------------------------------------------------------------------

EXTERNDEF   m16Start:BYTE
EXTERNDEF   m16Size:WORD
EXTERNDEF   mThunk16Attr:WORD
EXTERNDEF   m16Gdt:WORD
EXTERNDEF   m16GdtrBase:WORD
EXTERNDEF   mTransition:WORD

IA32_REGS   STRUC   4t
_EDI        DD      ?
_ESI        DD      ?
_EBP        DD      ?
_ESP        DD      ?
_EBX        DD      ?
_EDX        DD      ?
_ECX        DD      ?
_EAX        DD      ?
_DS         DW      ?
_ES         DW      ?
_FS         DW      ?
_GS         DW      ?
_EFLAGS     DQ      ?
_EIP        DD      ?
_CS         DW      ?
_SS         DW      ?
IA32_REGS   ENDS

    .const

m16Size         DW      InternalAsmThunk16 - m16Start
mThunk16Attr    DW      _ThunkAttr - m16Start
m16Gdt          DW      _NullSeg - m16Start
m16GdtrBase     DW      _16GdtrBase - m16Start
mTransition     DW      _EntryPoint - m16Start

    .code

m16Start    LABEL   BYTE

SavedGdt    LABEL   FWORD
            DW      ?
            DQ      ?

;------------------------------------------------------------------------------
; _BackFromUserCode() takes control in real mode after 'retf' has been executed
; by user code. It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_BackFromUserCode   PROC
    ;
    ; The order of saved registers on the stack matches the order they appears
    ; in IA32_REGS structure. This facilitates wrapper function to extract them
    ; into that structure.
    ;
    ; Some instructions for manipulation of segment registers have to be written
    ; in opcode since 64-bit MASM prevents accesses to those registers.
    ;
    DB      16h                         ; push ss
    DB      0eh                         ; push cs
    DB      66h
    call    @Base                       ; push eip
@Base:
    DB      66h
    push    0                           ; reserved high order 32 bits of EFlags
    pushf                               ; pushfd actually
    cli                                 ; disable interrupts
    push    gs
    push    fs
    DB      6                           ; push es
    DB      1eh                         ; push ds
    DB      66h, 60h                    ; pushad
    DB      66h, 0bah                   ; mov edx, imm32
_ThunkAttr  DD      ?
    test    dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
    jz      @1
    mov     eax, 15cd2401h              ; mov ax, 2401h & int 15h
    cli                                 ; disable interrupts
    jnc     @2
@1:
    test    dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
    jz      @2
    in      al, 92h
    or      al, 2
    out     92h, al                     ; deactivate A20M#
@2:
    mov     eax, ss
    lea     bp, [esp + sizeof (IA32_REGS)]
    ;
    ; rsi in the following 2 instructions is indeed bp in 16-bit code
    ;
    mov     word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
    DB      66h
    mov     ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
    shl     ax, 4                       ; shl eax, 4
    add     bp, ax                      ; add ebp, eax
    mov     ax, cs
    shl     ax, 4
    lea     ax, [eax + ebx + (@64BitCode - @Base)]
    DB      66h, 2eh, 89h, 87h          ; mov cs:[bx + (@64Eip - @Base)], eax
    DW      @64Eip - @Base
    DB      66h, 0b8h                   ; mov eax, imm32
SavedCr4    DD      ?
    mov     cr4, rax
    ;
    ; rdi in the instruction below is indeed bx in 16-bit code
    ;
    DB      66h, 2eh                    ; 2eh is "cs:" segment override
    lgdt    fword ptr [rdi + (SavedGdt - @Base)]
    DB      66h
    mov     ecx, 0c0000080h
    rdmsr
    or      ah, 1
    wrmsr
    DB      66h, 0b8h                   ; mov eax, imm32
SavedCr0    DD      ?
    mov     cr0, rax
    DB      66h, 0eah                   ; jmp far cs:@64Bit
@64Eip      DD      ?
SavedCs     DW      ?
@64BitCode:
    mov     rsp, r8                     ; restore stack
    ret
_BackFromUserCode   ENDP

_EntryPoint DD      _ToUserCode - m16Start
            DW      CODE16
_16Gdtr     LABEL   FWORD
            DW      GDT_SIZE - 1
_16GdtrBase DQ      _NullSeg
_16Idtr     FWORD   (1 SHL 10) - 1

;------------------------------------------------------------------------------
; _ToUserCode() takes control in real mode before passing control to user code.
; It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_ToUserCode PROC
    mov     ss, edx                     ; set new segment selectors
    mov     ds, edx
    mov     es, edx
    mov     fs, edx
    mov     gs, edx
    DB      66h
    mov     ecx, 0c0000080h
    mov     cr0, rax                    ; real mode starts at next instruction
    rdmsr
    and     ah, NOT 1
    wrmsr
    mov     cr4, rbp
    mov     ss, esi                     ; set up 16-bit stack segment
    mov     sp, bx                      ; set up 16-bit stack pointer
    DB      66h                         ; make the following call 32-bit
    call    @Base                       ; push eip
@Base:
    pop     bp                          ; ebp <- address of @Base
    push    [esp + sizeof (IA32_REGS) + 2]
    lea     eax, [rsi + (@RealMode - @Base)]    ; rsi is "bp" in 16-bit code
    push    rax
    retf                                ; execution begins at next instruction
@RealMode:
    DB      66h, 2eh                    ; CS and operand size override
    lidt    fword ptr [rsi + (_16Idtr - @Base)]
    DB      66h, 61h                    ; popad
    DB      1fh                         ; pop ds
    DB      07h                         ; pop es
    pop     fs
    pop     gs
    popf                                ; popfd
    lea     sp, [esp + 4]               ; skip high order 32 bits of EFlags
    DB      66h                         ; make the following retf 32-bit
    retf                                ; transfer control to user code
_ToUserCode ENDP

CODE16  = _16Code - $
DATA16  = _16Data - $
DATA32  = _32Data - $

_NullSeg    DQ      0
_16Code     LABEL   QWORD
            DW      -1
            DW      0
            DB      0
            DB      9bh
            DB      8fh                 ; 16-bit segment, 4GB limit
            DB      0
_16Data     LABEL   QWORD
            DW      -1
            DW      0
            DB      0
            DB      93h
            DB      8fh                 ; 16-bit segment, 4GB limit
            DB      0
_32Data     LABEL   QWORD
            DW      -1
            DW      0
            DB      0
            DB      93h
            DB      0cfh                ; 16-bit segment, 4GB limit
            DB      0

GDT_SIZE = $ - _NullSeg

;------------------------------------------------------------------------------
; IA32_REGISTER_SET *
; EFIAPI
; InternalAsmThunk16 (
;   IN      IA32_REGISTER_SET         *RegisterSet,
;   IN OUT  VOID                      *Transition
;   );
;------------------------------------------------------------------------------
InternalAsmThunk16  PROC    USES    rbp rbx rsi rdi
    mov     r10d, ds                    ; r9 ~ r11 are not accessible in 16-bit
    mov     r11d, es                    ; so use them for saving seg registers
    mov     r9d, ss
    push    fs
    push    gs
    mov     rsi, rcx
    movzx   r8d, (IA32_REGS ptr [rsi])._SS
    mov     edi, (IA32_REGS ptr [rsi])._ESP
    lea     rdi, [edi - (sizeof (IA32_REGS) + 4)]
    imul    eax, r8d, 16                ; eax <- r8d(stack segment) * 16
    mov     ebx, edi                    ; ebx <- stack for 16-bit code
    push    sizeof (IA32_REGS) / 4
    add     edi, eax                    ; edi <- linear address of 16-bit stack
    pop     rcx
    rep     movsd                       ; copy RegSet
    lea     ecx, [rdx + (SavedCr4 - m16Start)]
    mov     eax, edx                    ; eax <- transition code address
    and     edx, 0fh
    shl     eax, 12                     ; segment address in high order 16 bits
    lea     ax, [rdx + (_BackFromUserCode - m16Start)]  ; offset address
    stosd                               ; [edi] <- return address of user code
    sgdt    fword ptr [rcx + (SavedGdt - SavedCr4)]
    sidt    fword ptr [rsp + 38h]       ; save IDT stack in argument space
    mov     rax, cr0
    mov     [rcx + (SavedCr0 - SavedCr4)], eax
    and     eax, 7ffffffeh              ; clear PE, PG bits
    mov     rbp, cr4
    mov     [rcx], ebp                  ; save CR4 in SavedCr4
    and     ebp, 300h                   ; clear all but PCE and OSFXSR bits
    mov     esi, r8d                    ; esi <- 16-bit stack segment
    DB      6ah, DATA32                 ; push DATA32
    pop     rdx                         ; rdx <- 32-bit data segment selector
    lgdt    fword ptr [rcx + (_16Gdtr - SavedCr4)]
    mov     ss, edx
    pushfq
    lea     edx, [rdx + DATA16 - DATA32]
    lea     r8, @RetFromRealMode
    push    r8
    mov     r8d, cs
    mov     [rcx + (SavedCs - SavedCr4)], r8w
    mov     r8, rsp
    jmp     fword ptr [rcx + (_EntryPoint - SavedCr4)]
@RetFromRealMode:
    popfq
    lidt    fword ptr [rsp + 38h]       ; restore protected mode IDTR
    lea     eax, [rbp - sizeof (IA32_REGS)]
    pop     gs
    pop     fs
    mov     ss, r9d
    mov     es, r11d
    mov     ds, r10d
    ret
InternalAsmThunk16  ENDP

    END