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1.1 root 1: ;
1.1.1.6 root 2: ; Copyright (c) 2008-2009 TrueCrypt Foundation. All rights reserved.
1.1 root 3: ;
1.1.1.7 ! root 4: ; Governed by the TrueCrypt License 2.7 the full text of which is contained
1.1 root 5: ; in the file License.txt included in TrueCrypt binary and source code
6: ; distribution packages.
7: ;
8:
9: .MODEL tiny
10: .386
1.1.1.3 root 11: _TEXT SEGMENT USE16
1.1 root 12:
13: INCLUDE BootDefs.i
14:
1.1.1.3 root 15: ORG 7C00h ; Standard boot sector offset
1.1 root 16:
17: start:
18: ; BIOS executes boot sector from 0:7C00 or 7C0:0000 (default CD boot loader address).
1.1.1.3 root 19: ; Far jump to the next instruction sets IP to the standard offset 7C00.
1.1 root 20: db 0EAh ; jmp 0:main
21: dw main, 0
22:
1.1.1.3 root 23: loader_name_msg:
24: db ' TrueCrypt Boot Loader', 13, 10, 0
1.1 root 25:
1.1.1.6 root 26: main:
27: cli
1.1.1.2 root 28: xor ax, ax
1.1 root 29: mov ds, ax
1.1.1.6 root 30: mov ss, ax
31: mov sp, 7C00h
32: sti
33:
1.1.1.5 root 34: ; Display boot loader name
35: test byte ptr [start + TC_BOOT_SECTOR_USER_CONFIG_OFFSET], TC_BOOT_USER_CFG_FLAG_SILENT_MODE
36: jnz skip_loader_name_msg
37:
1.1.1.3 root 38: lea si, loader_name_msg
1.1 root 39: call print
1.1.1.5 root 40: skip_loader_name_msg:
41:
1.1.1.6 root 42: ; Determine boot loader segment
1.1 root 43: mov ax, TC_BOOT_LOADER_SEGMENT
44:
45: ; Check available memory
1.1.1.2 root 46: cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
1.1.1.3 root 47: jge memory_ok
1.1 root 48:
1.1.1.6 root 49: mov ax, TC_BOOT_LOADER_SEGMENT_LOW
50:
51: cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT_LOW / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
52: jge memory_ok
53:
1.1 root 54: ; Insufficient memory
55: mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
1.1.1.6 root 56:
1.1.1.3 root 57: memory_ok:
1.1.1.6 root 58: mov es, ax
1.1 root 59:
1.1.1.3 root 60: ; Clear BSS section
1.1 root 61: xor al, al
1.1.1.3 root 62: mov di, TC_COM_EXECUTABLE_OFFSET
63: mov cx, TC_BOOT_MEMORY_REQUIRED * 1024 - TC_COM_EXECUTABLE_OFFSET - 1
1.1.1.2 root 64: cld
1.1 root 65: rep stosb
66:
1.1.1.3 root 67: mov ax, es
68: sub ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16 ; Decompressor segment
69: mov es, ax
70:
71: ; Load decompressor
72: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR
73: retry_backup:
74: mov al, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
75: mov bx, TC_COM_EXECUTABLE_OFFSET
76: call read_sectors
77:
78: ; Decompressor checksum
79: xor ebx, ebx
80: mov si, TC_COM_EXECUTABLE_OFFSET
81: mov cx, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT * TC_LB_SIZE
82: call checksum
83: push ebx
84:
85: ; Load compressed boot loader
86: mov bx, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
87: mov cl, TC_BOOT_LOADER_START_SECTOR
88: mov al, TC_MAX_BOOT_LOADER_SECTOR_COUNT
89:
90: test backup_loader_used, 1
91: jz non_backup
92: mov al, TC_BOOT_LOADER_BACKUP_SECTOR_COUNT - TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
93: mov cl, TC_BOOT_LOADER_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
94:
95: non_backup:
96: call read_sectors
97:
98: ; Boot loader checksum
99: pop ebx
100: mov si, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
101: mov cx, word ptr [start + TC_BOOT_SECTOR_LOADER_LENGTH_OFFSET]
102: call checksum
103:
104: ; Verify checksum
105: cmp ebx, dword ptr [start + TC_BOOT_SECTOR_LOADER_CHECKSUM_OFFSET]
106: je checksum_ok
107:
108: ; Checksum incorrect - try using backup if available
109: test backup_loader_used, 1
110: jnz loader_damaged
111:
112: mov backup_loader_used, 1
113: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
1.1 root 114:
1.1.1.3 root 115: test TC_BOOT_CFG_FLAG_BACKUP_LOADER_AVAILABLE, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
116: jnz retry_backup
117:
118: loader_damaged:
119: lea si, loader_damaged_msg
120: call print
121: lea si, loader_name_msg
122: call print
1.1 root 123: jmp $
1.1.1.3 root 124: checksum_ok:
125:
126: ; Set up decompressor segment
127: mov ax, es
128: mov ds, ax
129: cli
130: mov ss, ax
131: mov sp, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE
132: sti
1.1 root 133:
1.1.1.3 root 134: push dx
135:
136: ; Decompress boot loader
137: push TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET + TC_GZIP_HEADER_SIZE ; Compressed data
138: push TC_MAX_BOOT_LOADER_DECOMPRESSED_SIZE ; Output buffer size
139: push TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE + TC_COM_EXECUTABLE_OFFSET ; Output buffer
140:
1.1.1.6 root 141: push cs
142: push decompressor_ret
143: push es
144: push TC_COM_EXECUTABLE_OFFSET
145: retf
146: decompressor_ret:
1.1.1.3 root 147:
148: add sp, 6
149: pop dx
150:
151: ; Restore boot sector segment
1.1.1.6 root 152: push cs
153: pop ds
1.1.1.3 root 154:
155: ; Check decompression result
156: test ax, ax
157: jz decompression_ok
158:
1.1.1.6 root 159: lea si, loader_damaged_msg
1.1.1.3 root 160: call print
161: jmp $
162: decompression_ok:
1.1 root 163:
164: ; DH = boot sector flags
165: mov dh, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
166:
1.1.1.3 root 167: ; Set up boot loader segment
1.1 root 168: mov ax, es
1.1.1.3 root 169: add ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16
170: mov es, ax
1.1 root 171: mov ds, ax
172: cli
173: mov ss, ax
1.1.1.3 root 174: mov sp, TC_BOOT_LOADER_STACK_TOP
1.1 root 175: sti
176:
1.1.1.3 root 177: ; Execute boot loader
178: push es
179: push TC_COM_EXECUTABLE_OFFSET
180: retf
181:
1.1 root 182: ; Print string
183: print:
184: xor bx, bx
185: mov ah, 0eh
1.1.1.3 root 186: cld
1.1 root 187:
188: @@: lodsb
189: test al, al
190: jz print_end
191:
192: int 10h
193: jmp @B
194:
195: print_end:
196: ret
1.1.1.3 root 197:
198: ; Read sectors of the first cylinder
199: read_sectors:
200: mov ch, 0 ; Cylinder
201: mov dh, 0 ; Head
202: ; DL = drive number passed from BIOS
203: mov ah, 2
204: int 13h
205: jnc read_ok
206:
207: lea si, disk_error_msg
208: call print
209: read_ok:
210: ret
211:
212: ; Calculate checksum
213: checksum:
214: push ds
215: push es
216: pop ds
217: xor eax, eax
218: cld
219:
220: @@: lodsb
221: add ebx, eax
222: rol ebx, 1
223: loop @B
224:
225: pop ds
226: ret
227:
228: backup_loader_used db 0
1.1 root 229:
1.1.1.3 root 230: disk_error_msg db 'Disk error', 13, 10, 7, 0
1.1.1.6 root 231: loader_damaged_msg db 7, 'Loader damaged! Use Rescue Disk: Repair Options > Restore', 0
1.1 root 232:
1.1.1.3 root 233: ORG 7C00h + 508
1.1 root 234: dw 0, 0AA55h ; Boot sector signature
235:
236: _TEXT ENDS
237: END start
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