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1.1 root 1: ;
2: ; Copyright (c) 2008 TrueCrypt Foundation. All rights reserved.
3: ;
1.1.1.4 ! root 4: ; Governed by the TrueCrypt License 2.5 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:
1.1.1.3 root 30: lea si, loader_name_msg
1.1 root 31: call print
32:
33: mov ax, TC_BOOT_LOADER_SEGMENT
1.1.1.3 root 34: mov es, ax ; Default boot loader segment
1.1 root 35:
36: ; Check available memory
1.1.1.2 root 37: cmp word ptr [ds:413h], TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED
1.1.1.3 root 38: jge memory_ok
1.1 root 39:
40: ; Insufficient memory
41: mov ax, TC_BOOT_LOADER_LOWMEM_SEGMENT
42: mov es, ax
1.1.1.3 root 43: memory_ok:
1.1 root 44:
1.1.1.3 root 45: ; Clear BSS section
1.1 root 46: xor al, al
1.1.1.3 root 47: mov di, TC_COM_EXECUTABLE_OFFSET
48: mov cx, TC_BOOT_MEMORY_REQUIRED * 1024 - TC_COM_EXECUTABLE_OFFSET - 1
1.1.1.2 root 49: cld
1.1 root 50: rep stosb
51:
1.1.1.3 root 52: mov ax, es
53: sub ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16 ; Decompressor segment
54: mov es, ax
55:
56: ; Load decompressor
57: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR
58: retry_backup:
59: mov al, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
60: mov bx, TC_COM_EXECUTABLE_OFFSET
61: call read_sectors
62:
63: ; Decompressor checksum
64: xor ebx, ebx
65: mov si, TC_COM_EXECUTABLE_OFFSET
66: mov cx, TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT * TC_LB_SIZE
67: call checksum
68: push ebx
69:
70: ; Load compressed boot loader
71: mov bx, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
72: mov cl, TC_BOOT_LOADER_START_SECTOR
73: mov al, TC_MAX_BOOT_LOADER_SECTOR_COUNT
74:
75: test backup_loader_used, 1
76: jz non_backup
77: mov al, TC_BOOT_LOADER_BACKUP_SECTOR_COUNT - TC_BOOT_LOADER_DECOMPRESSOR_SECTOR_COUNT
78: mov cl, TC_BOOT_LOADER_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
79:
80: non_backup:
81: call read_sectors
82:
83: ; Boot loader checksum
84: pop ebx
85: mov si, TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET
86: mov cx, word ptr [start + TC_BOOT_SECTOR_LOADER_LENGTH_OFFSET]
87: call checksum
88:
89: ; Verify checksum
90: cmp ebx, dword ptr [start + TC_BOOT_SECTOR_LOADER_CHECKSUM_OFFSET]
91: je checksum_ok
92:
93: ; Checksum incorrect - try using backup if available
94: test backup_loader_used, 1
95: jnz loader_damaged
96:
97: mov backup_loader_used, 1
98: mov cl, TC_BOOT_LOADER_DECOMPRESSOR_START_SECTOR + TC_BOOT_LOADER_BACKUP_SECTOR_COUNT
1.1 root 99:
1.1.1.3 root 100: test TC_BOOT_CFG_FLAG_BACKUP_LOADER_AVAILABLE, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
101: jnz retry_backup
102:
103: loader_damaged:
104: lea si, loader_damaged_msg
105: call print
106: lea si, loader_name_msg
107: call print
108: lea si, beep_msg
1.1 root 109: call print
110: jmp $
1.1.1.3 root 111: checksum_ok:
112:
113: ; Set up decompressor segment
114: mov ax, es
115: mov ds, ax
116: cli
117: mov ss, ax
118: mov sp, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE
119: sti
1.1 root 120:
1.1.1.3 root 121: push dx
122:
123: ; Decompress boot loader
124: push TC_BOOT_LOADER_COMPRESSED_BUFFER_OFFSET + TC_GZIP_HEADER_SIZE ; Compressed data
125: push TC_MAX_BOOT_LOADER_DECOMPRESSED_SIZE ; Output buffer size
126: push TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE + TC_COM_EXECUTABLE_OFFSET ; Output buffer
127:
128: mov word ptr [cs:decompressor_seg], es
129: db 9Ah ; call [decompressor_seg]:TC_COM_EXECUTABLE_OFFSET
130: dw TC_COM_EXECUTABLE_OFFSET
131: decompressor_seg:
132: dw 0
133:
134: add sp, 6
135: pop dx
136:
137: ; Restore boot sector segment
138: mov bx, cs
139: mov ds, bx
140:
141: ; Check decompression result
142: test ax, ax
143: jz decompression_ok
144:
145: lea si, decompression_err_msg
146: call print
147: jmp $
148: decompression_ok:
1.1 root 149:
150: ; DH = boot sector flags
151: mov dh, byte ptr [start + TC_BOOT_SECTOR_CONFIG_OFFSET]
152:
1.1.1.3 root 153: ; Set up boot loader segment
1.1 root 154: mov ax, es
1.1.1.3 root 155: add ax, TC_BOOT_LOADER_DECOMPRESSOR_MEMORY_SIZE / 16
156: mov es, ax
1.1 root 157: mov ds, ax
158: cli
159: mov ss, ax
1.1.1.3 root 160: mov sp, TC_BOOT_LOADER_STACK_TOP
1.1 root 161: sti
162:
1.1.1.3 root 163: ; Execute boot loader
164: push es
165: push TC_COM_EXECUTABLE_OFFSET
166: retf
167:
1.1 root 168: ; Print string
169: print:
170: xor bx, bx
171: mov ah, 0eh
1.1.1.3 root 172: cld
1.1 root 173:
174: @@: lodsb
175: test al, al
176: jz print_end
177:
178: int 10h
179: jmp @B
180:
181: print_end:
182: ret
1.1.1.3 root 183:
184: ; Read sectors of the first cylinder
185: read_sectors:
186: mov ch, 0 ; Cylinder
187: mov dh, 0 ; Head
188: ; DL = drive number passed from BIOS
189: mov ah, 2
190: int 13h
191: jnc read_ok
192:
193: lea si, disk_error_msg
194: call print
195: read_ok:
196: ret
197:
198: ; Calculate checksum
199: checksum:
200: push ds
201: push es
202: pop ds
203: xor eax, eax
204: cld
205:
206: @@: lodsb
207: add ebx, eax
208: rol ebx, 1
209: loop @B
210:
211: pop ds
212: ret
213:
214: backup_loader_used db 0
1.1 root 215:
1.1.1.3 root 216: beep_msg db 7, 0
217: disk_error_msg db 'Disk error', 13, 10, 7, 0
218: loader_damaged_msg db 'Loader damaged! Use Rescue Disk: Repair Options > Restore', 0
219: decompression_err_msg db 'Decompression error', 7, 0
1.1 root 220:
1.1.1.3 root 221: ORG 7C00h + 508
1.1 root 222: dw 0, 0AA55h ; Boot sector signature
223:
224: _TEXT ENDS
225: END start
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