;
; Derived from source code of TrueCrypt 7.1a, which is
; Copyright (c) 2008-2012 TrueCrypt Developers Association and which is governed
; by the TrueCrypt License 3.0.
;
; Modifications and additions to the original source code (contained in this file)
; and all other portions of this file are Copyright (c) 2013-2017 IDRIX
; and are governed by the Apache License 2.0 the full text of which is
; contained in the file License.txt included in VeraCrypt binary and source
; code distribution packages.
;
.MODEL tiny
.386
_TEXT SEGMENT USE16
INCLUDE BootDefs.i
ORG 7C00h ; Standard boot sector offset
start:
; BIOS executes boot sector from 0:7C00 or 7C0:0000 (default CD boot loader address).
; Far jump to the next instruction sets IP to the standard offset 7C00.
db 0EAh ; jmp 0:main
dw main, 0
loader_name_msg:
db ' VeraCrypt Boot Loader', 13, 10, 0
main:
cli
xor ax, ax
mov ds, ax
mov ss, ax
mov sp, 7C00h
sti
; Display boot loader name
test byte ptr [start + TC_BOOT_SECTOR_USER_CONFIG_OFFSET], TC_BOOT_USER_CFG_FLAG_SILENT_MODE
jnz skip_loader_name_msg
lea si, loader_name_msg
call print
skip_loader_name_msg:
; Determine boot loader segment
mov ax, word ptr [ds:413h] ;available kB from BIOS
sub ax, TC_BOOT_MEMORY_REQUIRED ;minus TC_BOOT_MEMORY_REQUIRED
jc mem_toolow
and ax, 0FFE0h ;32K align
shl ax, 6 ;convert kB to segment addr (*1024/16)
cmp ax, 8000h
jb mem_toolow ;we can't load below 8000h
cmp ax, TC_BOOT_LOADER_SEGMENT
jbe memory_ok ;don't load above TC_BOOT_LOADER_SEGMENT (9000h)
mov ax, TC_BOOT_LOADER_SEGMENT
jmp memory_ok
mem_toolow:
mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
memory_ok:
mov es, ax
; Clear BSS section
xor al, al
mov di, TC_COM_EXECUTABLE_OFFSET
mov cx, TC_BOOT_MEMORY_REQUIRED * 1024 - TC_COM_EXECUTABLE_OFFSET - 1
cld
rep stosb
mov ax, es
sub ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16 ; Decompressor segment
mov es, ax
; Load decompressor
mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR
retry_backup:
mov al, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
mov bx, TC_COM_EXECUTABLE_OFFSET
call read_sectors
; Decompressor checksum
xor ebx, ebx
mov si, TC_COM_EXECUTABLE_OFFSET
mov cx, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT * TC_LB_SIZE
call checksum
push ebx
; Load compressed boot loader
mov bx, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
mov cl, TC_BOOT_LOADER_START_SECTOR
mov al, TC_MAX_BOOT_LOADER_SECTOR_COUNT
test backup_loader_used, 1
jz non_backup
mov al, TC_BOOT_LOADER_BACKUP_SECTOR_COUNT - TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
mov cl, TC_BOOT_LOADER_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
non_backup:
call read_sectors
; Boot loader checksum
pop ebx
mov si, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
mov cx, word ptr [start + TC_BOOT_SECTOR_LOADER_LENGTH_OFFSET]
call checksum
; Verify checksum
cmp ebx, dword ptr [start + TC_BOOT_SECTOR_LOADER_CHECKSUM_OFFSET]
je checksum_ok
; Checksum incorrect - try using backup if available
test backup_loader_used, 1
jnz loader_damaged
mov backup_loader_used, 1
mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
test TC_BOOT_CFG_FLAG_BACKUP_LOADER_AVAILABLE, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
jnz retry_backup
loader_damaged:
lea si, loader_damaged_msg
call print
lea si, loader_name_msg
call print
jmp $
checksum_ok:
; Set up decompressor segment
mov ax, es
mov ds, ax
cli
mov ss, ax
mov sp, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE
sti
push dx
; Decompress boot loader
mov cx, word ptr [start + TC_BOOT_SECTOR_LOADER_LENGTH_OFFSET]
sub cx, TC_GZIP_HEADER_SIZE
push cx ; Compressed data size
push TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET + TC_GZIP_HEADER_SIZE ; Compressed data
push TC_MAX_BOOT_LOADER_DECOMPRESSED_SIZE ; Output buffer size
push TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE + TC_COM_EXECUTABLE_OFFSET ; Output buffer
push cs
push decompressor_ret
push es
push TC_COM_EXECUTABLE_OFFSET
retf
decompressor_ret:
add sp, 8
pop dx
; Restore boot sector segment
push cs
pop ds
; Check decompression result
test ax, ax
jz decompression_ok
lea si, loader_damaged_msg
call print
jmp $
decompression_ok:
; DH = boot sector flags
mov dh, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
; Set up boot loader segment
mov ax, es
add ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16
mov es, ax
mov ds, ax
cli
mov ss, ax
mov sp, TC_BOOT_LOADER_STACK_TOP
sti
; Execute boot loader
push es
push TC_COM_EXECUTABLE_OFFSET
retf
; Print string
print:
xor bx, bx
mov ah, 0eh
cld
@@: lodsb
test al, al
jz print_end
int 10h
jmp @B
print_end:
ret
; Read sectors of the first cylinder
read_sectors:
mov ch, 0 ; Cylinder
mov dh, 0 ; Head
; DL = drive number passed from BIOS
mov ah, 2
int 13h
jnc read_ok
lea si, disk_error_msg
call print
read_ok:
ret
; Calculate checksum
checksum:
push ds
push es
pop ds
xor eax, eax
cld
@@: lodsb
add ebx, eax
rol ebx, 1
loop @B
pop ds
ret
backup_loader_used db 0
disk_error_msg db 'Disk error', 13, 10, 7, 0
loader_damaged_msg db 7, 'Loader damaged! Repair with Rescue Disk', 0
ORG 7C00h + 510
dw 0AA55h ; Boot sector signature
_TEXT ENDS
END start
a id='n57' href='#n57'>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
|