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1.1 root 1: ;
2: ; Copyright (c) 2008 TrueCrypt Foundation. All rights reserved.
3: ;
1.1.1.5 ! root 4: ; Governed by the TrueCrypt License 2.6 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:
26: main:
1.1.1.2 root 27: xor ax, ax
1.1 root 28: mov ds, ax
29:
1.1.1.5 ! root 30: ; Display boot loader name
! 31: test byte ptr [start + TC_BOOT_SECTOR_USER_CONFIG_OFFSET], TC_BOOT_USER_CFG_FLAG_SILENT_MODE
! 32: jnz skip_loader_name_msg
! 33:
1.1.1.3 root 34: lea si, loader_name_msg
1.1 root 35: call print
1.1.1.5 ! root 36: skip_loader_name_msg:
! 37:
1.1 root 38: mov ax, TC_BOOT_LOADER_SEGMENT
1.1.1.3 root 39: mov es, ax ; Default boot loader segment
1.1 root 40:
41: ; Check available memory
1.1.1.2 root 42: cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
1.1.1.3 root 43: jge memory_ok
1.1 root 44:
45: ; Insufficient memory
46: mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
47: mov es, ax
1.1.1.3 root 48: memory_ok:
1.1 root 49:
1.1.1.3 root 50: ; Clear BSS section
1.1 root 51: xor al, al
1.1.1.3 root 52: mov di, TC_COM_EXECUTABLE_OFFSET
53: mov cx, TC_BOOT_MEMORY_REQUIRED * 1024 - TC_COM_EXECUTABLE_OFFSET - 1
1.1.1.2 root 54: cld
1.1 root 55: rep stosb
56:
1.1.1.3 root 57: mov ax, es
58: sub ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16 ; Decompressor segment
59: mov es, ax
60:
61: ; Load decompressor
62: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR
63: retry_backup:
64: mov al, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
65: mov bx, TC_COM_EXECUTABLE_OFFSET
66: call read_sectors
67:
68: ; Decompressor checksum
69: xor ebx, ebx
70: mov si, TC_COM_EXECUTABLE_OFFSET
71: mov cx, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT * TC_LB_SIZE
72: call checksum
73: push ebx
74:
75: ; Load compressed boot loader
76: mov bx, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
77: mov cl, TC_BOOT_LOADER_START_SECTOR
78: mov al, TC_MAX_BOOT_LOADER_SECTOR_COUNT
79:
80: test backup_loader_used, 1
81: jz non_backup
82: mov al, TC_BOOT_LOADER_BACKUP_SECTOR_COUNT - TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
83: mov cl, TC_BOOT_LOADER_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
84:
85: non_backup:
86: call read_sectors
87:
88: ; Boot loader checksum
89: pop ebx
90: mov si, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
91: mov cx, word ptr [start + TC_BOOT_SECTOR_LOADER_LENGTH_OFFSET]
92: call checksum
93:
94: ; Verify checksum
95: cmp ebx, dword ptr [start + TC_BOOT_SECTOR_LOADER_CHECKSUM_OFFSET]
96: je checksum_ok
97:
98: ; Checksum incorrect - try using backup if available
99: test backup_loader_used, 1
100: jnz loader_damaged
101:
102: mov backup_loader_used, 1
103: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
1.1 root 104:
1.1.1.3 root 105: test TC_BOOT_CFG_FLAG_BACKUP_LOADER_AVAILABLE, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
106: jnz retry_backup
107:
108: loader_damaged:
109: lea si, loader_damaged_msg
110: call print
111: lea si, loader_name_msg
112: call print
113: lea si, beep_msg
1.1 root 114: call print
115: jmp $
1.1.1.3 root 116: checksum_ok:
117:
118: ; Set up decompressor segment
119: mov ax, es
120: mov ds, ax
121: cli
122: mov ss, ax
123: mov sp, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE
124: sti
1.1 root 125:
1.1.1.3 root 126: push dx
127:
128: ; Decompress boot loader
129: push TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET + TC_GZIP_HEADER_SIZE ; Compressed data
130: push TC_MAX_BOOT_LOADER_DECOMPRESSED_SIZE ; Output buffer size
131: push TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE + TC_COM_EXECUTABLE_OFFSET ; Output buffer
132:
133: mov word ptr [cs:decompressor_seg], es
134: db 9Ah ; call [decompressor_seg]:TC_COM_EXECUTABLE_OFFSET
135: dw TC_COM_EXECUTABLE_OFFSET
136: decompressor_seg:
137: dw 0
138:
139: add sp, 6
140: pop dx
141:
142: ; Restore boot sector segment
143: mov bx, cs
144: mov ds, bx
145:
146: ; Check decompression result
147: test ax, ax
148: jz decompression_ok
149:
150: lea si, decompression_err_msg
151: call print
152: jmp $
153: decompression_ok:
1.1 root 154:
155: ; DH = boot sector flags
156: mov dh, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
157:
1.1.1.3 root 158: ; Set up boot loader segment
1.1 root 159: mov ax, es
1.1.1.3 root 160: add ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16
161: mov es, ax
1.1 root 162: mov ds, ax
163: cli
164: mov ss, ax
1.1.1.3 root 165: mov sp, TC_BOOT_LOADER_STACK_TOP
1.1 root 166: sti
167:
1.1.1.3 root 168: ; Execute boot loader
169: push es
170: push TC_COM_EXECUTABLE_OFFSET
171: retf
172:
1.1 root 173: ; Print string
174: print:
175: xor bx, bx
176: mov ah, 0eh
1.1.1.3 root 177: cld
1.1 root 178:
179: @@: lodsb
180: test al, al
181: jz print_end
182:
183: int 10h
184: jmp @B
185:
186: print_end:
187: ret
1.1.1.3 root 188:
189: ; Read sectors of the first cylinder
190: read_sectors:
191: mov ch, 0 ; Cylinder
192: mov dh, 0 ; Head
193: ; DL = drive number passed from BIOS
194: mov ah, 2
195: int 13h
196: jnc read_ok
197:
198: lea si, disk_error_msg
199: call print
200: read_ok:
201: ret
202:
203: ; Calculate checksum
204: checksum:
205: push ds
206: push es
207: pop ds
208: xor eax, eax
209: cld
210:
211: @@: lodsb
212: add ebx, eax
213: rol ebx, 1
214: loop @B
215:
216: pop ds
217: ret
218:
219: backup_loader_used db 0
1.1 root 220:
1.1.1.3 root 221: beep_msg db 7, 0
222: disk_error_msg db 'Disk error', 13, 10, 7, 0
223: loader_damaged_msg db 'Loader damaged! Use Rescue Disk: Repair Options > Restore', 0
1.1.1.5 ! root 224: decompression_err_msg db 'DC', 0
1.1 root 225:
1.1.1.3 root 226: ORG 7C00h + 508
1.1 root 227: dw 0, 0AA55h ; Boot sector signature
228:
229: _TEXT ENDS
230: END start
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