中国DOS联盟

发信人: Netguy (造梦人), 信区: DOS
标 题: 硬盘主引导程序剖析
发信站: BBS 水木清华站 (Wed Aug 27 13:32:41 1997)

如果是从硬盘起动,则
开机起动时,ROM BIOS程序把硬盘上0面0道1扇区的主引导程序加载到内存0000:7C00处,并
开始执行它.因此,下面的第一条指令CLI的绝对地址是0000:7C00H
通过修改主引导扇区,可以实现一定的加密效果,若被病毒利用...

偏移 机器码 符号指令 说明
==============================================================================
0000 FA CLI ;屏蔽中断
0001 33C0 XOR AX,AX
0003 8ED0 MOV SS,AX ;(SS)=0000H
0005 BC007C MOV SP,7C00 ;(SP)=7C00H
0008 8BF4 MOV SI,SP ;(SI)=7C00H
000A 50 PUSH AX
000B 07 POP ES ;(ES)=0000H
000C 50 PUSH AX
000D 1F POP DS ;(DS)=0000H
000E FB STI
000F FC CLD
0010 BF0006 MOV DI,0600
0013 B90001 MOV CX,0100 ;共512字节
0016 F2 REPNZ
0017 A5 MOVSW ;主引导程序把自己从0000:7C00处搬到
;0000:0600处,为Dos分区的引导程序腾
;出空间
0018 EA1D060000 JMP 0000:061D ;跳到0000:061D处继续执行,实际上就是
;执行下面的MOV指令(001D偏移处)
001D BEBE07 MOV SI,07BE ;07BE-0600=01BE,01BE是分区表的首址
0020 B304 MOV BL,04 ;分区表最多4项,即最多4个分区
0022 803C80 CMP BYTE PTR ,80 ;80H表示活动分区
0025 740E JZ 0035 ;找到活动分区则跳走
0027 803C00 CMP BYTE PTR ,00 ;00H为有效分区的标志
002A 751C JNZ 0048 ;既非80H亦非00H则分区表无效
002C 83C610 ADD SI,+10 ;下一个分区表项,每项16字节
002F FECB DEC BL ;循环计数减一
0031 75EF JNZ 0022 ;检查下一个分区表项
0033 CD18 INT 18 ;4个都不能引导则进入ROM Basic
0035 8B14 MOV DX,
0037 8B4C02 MOV CX, ;取活动分区的引导扇区的面,柱面,扇区
003A 8BEE MOV BP,SI ;然后继续检查后面的分区表项
003C 83C610 ADD SI,+10
003F FECB DEC BL
0041 741A JZ 005D ;4个都查完则去引导活动分区
0043 803C00 CMP BYTE PTR ,00 ;00H为分区有效标志
0046 74F4 JZ 003C ;此分区表项有效则继续查下一个
0048 BE8B06 MOV SI,068B ;068B-0600=018B,取"无效分区"字符串
004B AC LODSB ;从字符串中取一字符
004C 3C00 CMP AL,00 ;00H表示串尾
004E 740B JZ 005B ;串显示完了则进入死循环
0050 56 PUSH SI
0051 BB0700 MOV BX,0007
0054 B40E MOV AH,0E
0056 CD10 INT 10 ;显示一个字符
0058 5E POP SI
0059 EBF0 JMP 004B ;循环显示下一个字符
005B EBFE JMP 005B ;此处为死循环
005D BF0500 MOV DI,0005 ;读入活动分区的引导扇,最多试读5次
0060 BB007C MOV BX,7C00
0063 B80102 MOV AX,0201
0066 57 PUSH DI
0067 CD13 INT 13 ;读
0069 5F POP DI
006A 730C JNB 0078 ;读盘成功则跳走
006C 33C0 XOR AX,AX
006E CD13 INT 13 ;读失败则复位磁盘
0070 4F DEC DI
0071 75ED JNZ 0060 ;不到5次则再试读
0073 BEA306 MOV SI,06A3 ;06A3-0600=00A3,即"Error loading"串
0076 EBD3 JMP 004B ;去显示字符串,然后进入死循环
0078 BEC206 MOV SI,06C2 ;06C2-0600=00C2,即"Missing.."串
0076 EBD3 JMP 004B ;去显示字符串,然后进入死循环
0078 BEC206 MOV SI,06C2 ;06C2-0600=00C2,即"Missing.."串
007B BFFE7D MOV DI,7DFE ;7DFE-7C00=01FE,即活动分区的引导扇
;区的最后两字节的首址
007E 813D55AA CMP WORD PTR ,AA55;最后两字节为AA55H则有效
0082 75C7 JNZ 004B ;无效则显示字符串并进入死循环
0084 8BF5 MOV SI,BP
0086 EA007C0000 JMP 0000:7C00 ;有效则跳去引导该分区
0080 49 6E 76 61 6C Inval
0090 69 64 20 70 61 72 74 69-74 69 6F 6E 20 74 61 62 id partition tab
00A0 6C 65 00 45 72 72 6F 72-20 6C 6F 61 64 69 6E 67 le.Error loading
00B0 20 6F 70 65 72 61 74 69-6E 67 20 73 79 73 74 65 operating syste
00C0 6D 00 4D 69 73 73 69 6E-67 20 6F 70 65 72 61 74 m.Missing operat
00D0 69 6E 67 20 73 79 73 74-65 6D 00 00 FB 4C 38 1D ing system...L8.
00E0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
00F0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0100 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0110 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0120 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0130 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0140 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0150 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0160 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0170 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0180 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0190 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
01A0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
01B0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 80 01 ................;分区表
01C0 01 00 06 0F 7F 9C 3F 00-00 00 F1 59 06 00 00 00 ......?....Y....
01D0 41 9D 05 0F FF 38 30 5A-06 00 40 56 06 00 00 00 A....80Z..@V....
01E0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
01F0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 55 AA ..............U.

Dos的引导程序我还要查些资料,下次吧.
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※ 来源:·BBS 水木清华站 bbs.net.tsinghua.edu.cn·

(本文采用S-Term文章拷贝脚本拷贝)
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THANK YOU!