概述
这个实验是有名的二进制拆弹实验。这是实验指导书和实验源程序。通过阅读汇编代码来判断能够“拆弹”的目标字符串。通过这个实验，学到了怎样读懂x86-64汇编和用gdb来调试汇编代码。
实验内容
给的文档有三个文件，分别是bomb 、bomb.c、README。
objdump -d bomb > bomb.s获得可执行程序bomb的汇编代码。实验共有6个phase，也就是通过6种不同的方法寻找目标字符串，难度逐步增加。
1. phase_1
下面这段汇编通过调用strings_not_equal函数来判断输入字符串（首地址在%rdi中）和目标字符串（首地址在%rsi中）是否不等来判断是否解开炸弹。mov $0x402400,%esi直接指明目标字符串位置，十分简单。
0000000000400ee0 :
400ee0: 48 83 ec 08 sub $0x8,%rsp
400ee4: be 00 24 40 00 mov $0x402400,%esi
400ee9: e8 4a 04 00 00 callq 401338
400eee: 85 c0 test %eax,%eax
400ef0: 74 05 je 400ef7
400ef2: e8 43 05 00 00 callq 40143a
400ef7: 48 83 c4 08 add $0x8,%rsp
400efb: c3 retq
2. phase_2
这段汇编代码首先 read_six_numbers到寄存器%rsp，%rsp+4，%rsp+8，%rsp+12，%rsp+16，%rsp+20上，然后检测它们是否与1,2,4,8,16,32分别相当。说白了这就是一个公比为2的等比数列。从
400f1a: 01 c0 add %eax,%eax; 400f1c: 39 03 cmp %eax,(%rbx)中可以琢磨些端倪。
0000000000400efc :
400efc: 55 push %rbp
400efd: 53 push %rbx
400efe: 48 83 ec 28 sub $0x28,%rsp
400f02: 48 89 e6 mov %rsp,%rsi
400f05: e8 52 05 00 00 callq 40145c
400f0a: 83 3c 24 01 cmpl $0x1,(%rsp)
400f0e: 74 20 je 400f30
400f10: e8 25 05 00 00 callq 40143a
400f15: eb 19 jmp 400f30
400f17: 8b 43 fc mov -0x4(%rbx),%eax
400f1a: 01 c0 add %eax,%eax
400f1c: 39 03 cmp %eax,(%rbx)
400f1e: 74 05 je 400f25
400f20: e8 15 05 00 00 callq 40143a
400f25: 48 83 c3 04 add $0x4,%rbx
400f29: 48 39 eb cmp %rbp,%rbx
400f2c: 75 e9 jne 400f17
400f2e: eb 0c jmp 400f3c
400f30: 48 8d 5c 24 04 lea 0x4(%rsp),%rbx
400f35: 48 8d 6c 24 18 lea 0x18(%rsp),%rbp
400f3a: eb db jmp 400f17
400f3c: 48 83 c4 28 add $0x28,%rsp
400f40: 5b pop %rbx
400f41: 5d pop %rbp
400f42: c3 retq
3. phase_3
查看地址0x4025cf存的什么，发现是"%d %d"，从后续的sscanf函数的调用来看，应该是要求用户输入两个整数。
通过后文奇怪的跳转
jmpq *0x402470(,%rax,8)和一系列的mov然后跳转可以想起这是switch语句结构。那么程序是将第一个数作为switch的key，然后调到特定的地址获得相应的value。查看0x402470对应的跳转表内容
| number1 | number2 |
|---|---|
| 0 | 0xcf |
| 1 | 0x137 |
| 2 | 0x2c3 |
| 3 | 0x100 |
| 4 | 0x185 |
| 5 | 0xce |
| 6 | 0x2aa |
| 7 | 0x147 |
都可以通过，不过要记得输入十进制数。
0000000000400f43 :
400f43: 48 83 ec 18 sub $0x18,%rsp
400f47: 48 8d 4c 24 0c lea 0xc(%rsp),%rcx
400f4c: 48 8d 54 24 08 lea 0x8(%rsp),%rdx
400f51: be cf 25 40 00 mov $0x4025cf,%esi
400f56: b8 00 00 00 00 mov $0x0,%eax
400f5b: e8 90 fc ff ff callq 400bf0 <__isoc99_sscanf@plt>
400f60: 83 f8 01 cmp $0x1,%eax
400f63: 7f 05 jg 400f6a
400f65: e8 d0 04 00 00 callq 40143a
400f6a: 83 7c 24 08 07 cmpl $0x7,0x8(%rsp)
400f6f: 77 3c ja 400fad
400f71: 8b 44 24 08 mov 0x8(%rsp),%eax
400f75: ff 24 c5 70 24 40 00 jmpq *0x402470(,%rax,8)
400f7c: b8 cf 00 00 00 mov $0xcf,%eax
400f81: eb 3b jmp 400fbe
400f83: b8 c3 02 00 00 mov $0x2c3,%eax
400f88: eb 34 jmp 400fbe
400f8a: b8 00 01 00 00 mov $0x100,%eax
400f8f: eb 2d jmp 400fbe
400f91: b8 85 01 00 00 mov $0x185,%eax
400f96: eb 26 jmp 400fbe
400f98: b8 ce 00 00 00 mov $0xce,%eax
400f9d: eb 1f jmp 400fbe
400f9f: b8 aa 02 00 00 mov $0x2aa,%eax
400fa4: eb 18 jmp 400fbe
400fa6: b8 47 01 00 00 mov $0x147,%eax
400fab: eb 11 jmp 400fbe
400fad: e8 88 04 00 00 callq 40143a
400fb2: b8 00 00 00 00 mov $0x0,%eax
400fb7: eb 05 jmp 400fbe
400fb9: b8 37 01 00 00 mov $0x137,%eax
400fbe: 3b 44 24 0c cmp 0xc(%rsp),%eax
400fc2: 74 05 je 400fc9
400fc4: e8 71 04 00 00 callq 40143a
400fc9: 48 83 c4 18 add $0x18,%rsp
400fcd: c3 retq
4. phase_4
在这个phase中也是读入两个数，且第一个数小于<=0xe，第二个数为0。第一个数调用函数func4，然后func4里面又是奇怪的递归，最后可用的结果是
| number1 | number2 |
|---|---|
| 1 | 0 |
| 3 | 0 |
| 7 | 0 |
兴许是满足X(i+1) = 2X(i)+1这种关系的序列。
000000000040100c :
40100c: 48 83 ec 18 sub $0x18,%rsp
401010: 48 8d 4c 24 0c lea 0xc(%rsp),%rcx
401015: 48 8d 54 24 08 lea 0x8(%rsp),%rdx
40101a: be cf 25 40 00 mov $0x4025cf,%esi
40101f: b8 00 00 00 00 mov $0x0,%eax
401024: e8 c7 fb ff ff callq 400bf0 <__isoc99_sscanf@plt>
401029: 83 f8 02 cmp $0x2,%eax
40102c: 75 07 jne 401035
40102e: 83 7c 24 08 0e cmpl $0xe,0x8(%rsp)
401033: 76 05 jbe 40103a
401035: e8 00 04 00 00 callq 40143a
40103a: ba 0e 00 00 00 mov $0xe,%edx
40103f: be 00 00 00 00 mov $0x0,%esi
401044: 8b 7c 24 08 mov 0x8(%rsp),%edi
401048: e8 81 ff ff ff callq 400fce
40104d: 85 c0 test %eax,%eax
40104f: 75 07 jne 401058
401051: 83 7c 24 0c 00 cmpl $0x0,0xc(%rsp)
401056: 74 05 je 40105d
401058: e8 dd 03 00 00 callq 40143a
40105d: 48 83 c4 18 add $0x18,%rsp
401061: c3 retq
5. phase_5
phase_5先验证输入字符串长度是否为6。然后通过取每个字符的ASCII码作为下标获得在指定字符串str1中的字符，新字符组成的字符串str2应该相等。
0000000000401062 :
401062: 53 push %rbx
401063: 48 83 ec 20 sub $0x20,%rsp
401067: 48 89 fb mov %rdi,%rbx
40106a: 64 48 8b 04 25 28 00 mov %fs:0x28,%rax
401071: 00 00
401073: 48 89 44 24 18 mov %rax,0x18(%rsp)
401078: 31 c0 xor %eax,%eax
40107a: e8 9c 02 00 00 callq 40131b
40107f: 83 f8 06 cmp $0x6,%eax
401082: 74 4e je 4010d2
401084: e8 b1 03 00 00 callq 40143a
401089: eb 47 jmp 4010d2
40108b: 0f b6 0c 03 movzbl (%rbx,%rax,1),%ecx
40108f: 88 0c 24 mov %cl,(%rsp)
401092: 48 8b 14 24 mov (%rsp),%rdx
401096: 83 e2 0f and $0xf,%edx
401099: 0f b6 92 b0 24 40 00 movzbl 0x4024b0(%rdx),%edx
4010a0: 88 54 04 10 mov %dl,0x10(%rsp,%rax,1)
4010a4: 48 83 c0 01 add $0x1,%rax
4010a8: 48 83 f8 06 cmp $0x6,%rax
4010ac: 75 dd jne 40108b
4010ae: c6 44 24 16 00 movb $0x0,0x16(%rsp)
4010b3: be 5e 24 40 00 mov $0x40245e,%esi
4010b8: 48 8d 7c 24 10 lea 0x10(%rsp),%rdi
4010bd: e8 76 02 00 00 callq 401338
4010c2: 85 c0 test %eax,%eax
4010c4: 74 13 je 4010d9
4010c6: e8 6f 03 00 00 callq 40143a
4010cb: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
4010d0: eb 07 jmp 4010d9
4010d2: b8 00 00 00 00 mov $0x0,%eax
4010d7: eb b2 jmp 40108b
4010d9: 48 8b 44 24 18 mov 0x18(%rsp),%rax
4010de: 64 48 33 04 25 28 00 xor %fs:0x28,%rax
4010e5: 00 00
4010e7: 74 05 je 4010ee
4010e9: e8 42 fa ff ff callq 400b30 <__stack_chk_fail@plt>
4010ee: 48 83 c4 20 add $0x20,%rsp
4010f2: 5b pop %rbx
4010f3: c3 retq
最后结果为"ionefg"。
- phase_6
这个phase的汇编代码超级长，解析起来异常痛苦。大概过程是
- 读取6个数，这6个数应该是1~6中的任一个，且互不相同
- 然后
7-x获得一个新数y - 新序列数y对应链表中的第y个数，按照输入数的顺序重排该链表
- 重排后的链表应该是非递增的
关键是找到链表中的元素，0x6032d0是链表的起始地址。查看链表为
node1(0x14c)-->node2(0xa8)-->node3(0x39c)-->node4(0x2b3)-->node5(0x(1dd)-->node6(0x1bb)。按照降序排列应为node3-->node4-->node5-->node6-->node1-->node2。反推输入序列为为4 3 2 1 6 5。
00000000004010f4 :
4010f4: 41 56 push %r14
4010f6: 41 55 push %r13
4010f8: 41 54 push %r12
4010fa: 55 push %rbp
4010fb: 53 push %rbx
4010fc: 48 83 ec 50 sub $0x50,%rsp
401100: 49 89 e5 mov %rsp,%r13
401103: 48 89 e6 mov %rsp,%rsi
401106: e8 51 03 00 00 callq 40145c
40110b: 49 89 e6 mov %rsp,%r14
40110e: 41 bc 00 00 00 00 mov $0x0,%r12d
401114: 4c 89 ed mov %r13,%rbp
401117: 41 8b 45 00 mov 0x0(%r13),%eax
40111b: 83 e8 01 sub $0x1,%eax
40111e: 83 f8 05 cmp $0x5,%eax
401121: 76 05 jbe 401128
401123: e8 12 03 00 00 callq 40143a
401128: 41 83 c4 01 add $0x1,%r12d
40112c: 41 83 fc 06 cmp $0x6,%r12d
401130: 74 21 je 401153
401132: 44 89 e3 mov %r12d,%ebx
401135: 48 63 c3 movslq %ebx,%rax
401138: 8b 04 84 mov (%rsp,%rax,4),%eax
40113b: 39 45 00 cmp %eax,0x0(%rbp)
40113e: 75 05 jne 401145
401140: e8 f5 02 00 00 callq 40143a
401145: 83 c3 01 add $0x1,%ebx
401148: 83 fb 05 cmp $0x5,%ebx
40114b: 7e e8 jle 401135
40114d: 49 83 c5 04 add $0x4,%r13
401151: eb c1 jmp 401114
401153: 48 8d 74 24 18 lea 0x18(%rsp),%rsi
401158: 4c 89 f0 mov %r14,%rax
40115b: b9 07 00 00 00 mov $0x7,%ecx
401160: 89 ca mov %ecx,%edx
401162: 2b 10 sub (%rax),%edx
401164: 89 10 mov %edx,(%rax)
401166: 48 83 c0 04 add $0x4,%rax
40116a: 48 39 f0 cmp %rsi,%rax
40116d: 75 f1 jne 401160
40116f: be 00 00 00 00 mov $0x0,%esi
401174: eb 21 jmp 401197
401176: 48 8b 52 08 mov 0x8(%rdx),%rdx
40117a: 83 c0 01 add $0x1,%eax
40117d: 39 c8 cmp %ecx,%eax
40117f: 75 f5 jne 401176
401181: eb 05 jmp 401188
401183: ba d0 32 60 00 mov $0x6032d0,%edx
401188: 48 89 54 74 20 mov %rdx,0x20(%rsp,%rsi,2)
40118d: 48 83 c6 04 add $0x4,%rsi
401191: 48 83 fe 18 cmp $0x18,%rsi
401195: 74 14 je 4011ab
401197: 8b 0c 34 mov (%rsp,%rsi,1),%ecx
40119a: 83 f9 01 cmp $0x1,%ecx
40119d: 7e e4 jle 401183
40119f: b8 01 00 00 00 mov $0x1,%eax
4011a4: ba d0 32 60 00 mov $0x6032d0,%edx
4011a9: eb cb jmp 401176
4011ab: 48 8b 5c 24 20 mov 0x20(%rsp),%rbx
4011b0: 48 8d 44 24 28 lea 0x28(%rsp),%rax
4011b5: 48 8d 74 24 50 lea 0x50(%rsp),%rsi
4011ba: 48 89 d9 mov %rbx,%rcx
4011bd: 48 8b 10 mov (%rax),%rdx
4011c0: 48 89 51 08 mov %rdx,0x8(%rcx)
4011c4: 48 83 c0 08 add $0x8,%rax
4011c8: 48 39 f0 cmp %rsi,%rax
4011cb: 74 05 je 4011d2
4011cd: 48 89 d1 mov %rdx,%rcx
4011d0: eb eb jmp 4011bd
4011d2: 48 c7 42 08 00 00 00 movq $0x0,0x8(%rdx)
4011d9: 00
4011da: bd 05 00 00 00 mov $0x5,%ebp
4011df: 48 8b 43 08 mov 0x8(%rbx),%rax
4011e3: 8b 00 mov (%rax),%eax
4011e5: 39 03 cmp %eax,(%rbx)
4011e7: 7d 05 jge 4011ee
4011e9: e8 4c 02 00 00 callq 40143a
4011ee: 48 8b 5b 08 mov 0x8(%rbx),%rbx
4011f2: 83 ed 01 sub $0x1,%ebp
4011f5: 75 e8 jne 4011df
4011f7: 48 83 c4 50 add $0x50,%rsp
4011fb: 5b pop %rbx
4011fc: 5d pop %rbp
4011fd: 41 5c pop %r12
4011ff: 41 5d pop %r13
401201: 41 5e pop %r14
401203: c3 retq