可执行文件中通用字符串的含义? [英] Meaning of a Common String In Executables?
问题描述
在Mach-O 64位可执行文件和ELF 64位LSB可执行文件中，似乎存在一些外观相似的长字母数字字符串，以及其他非字母数字符号:
There appear to be some similar-looking long alphanumeric strings that commonly occur in Mach-O 64 bit executables and ELF 64-bit LSB executables among other symbols that are not alphanumeric:
cat /bin/bash | grep -c "AWAVAUATSH"
有181个结果，
cat /usr/bin/gzip | grep -c "AWAVAUATSH"
有9个结果.
这些字符串是什么?
推荐答案
有趣的问题.由于我不知道答案，因此请按照以下步骤找出答案:
Interesting question. Since I didn't know the answer, here are the steps I took to figure it out:
该字符串在文件中的何处出现?
Where in the file does the string occur?
strings -otx /bin/gzip | grep AWAVAUATUSH
35e0 AWAVAUATUSH
69a0 AWAVAUATUSH
7920 AWAVAUATUSH
8900 AWAVAUATUSH
92a0 AWAVAUATUSH
其中哪个部分?
readelf -WS /bin/gzip
There are 28 section headers, starting at offset 0x16860:
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] .interp PROGBITS 0000000000400238 000238 00001c 00 A 0 0 1
[ 2] .note.ABI-tag NOTE 0000000000400254 000254 000020 00 A 0 0 4
[ 3] .note.gnu.build-id NOTE 0000000000400274 000274 000024 00 A 0 0 4
[ 4] .gnu.hash GNU_HASH 0000000000400298 000298 000038 00 A 5 0 8
[ 5] .dynsym DYNSYM 00000000004002d0 0002d0 000870 18 A 6 1 8
[ 6] .dynstr STRTAB 0000000000400b40 000b40 000360 00 A 0 0 1
[ 7] .gnu.version VERSYM 0000000000400ea0 000ea0 0000b4 02 A 5 0 2
[ 8] .gnu.version_r VERNEED 0000000000400f58 000f58 000080 00 A 6 1 8
[ 9] .rela.dyn RELA 0000000000400fd8 000fd8 000090 18 A 5 0 8
[10] .rela.plt RELA 0000000000401068 001068 0007e0 18 A 5 12 8
[11] .init PROGBITS 0000000000401848 001848 00001a 00 AX 0 0 4
[12] .plt PROGBITS 0000000000401870 001870 000550 10 AX 0 0 16
[13] .text PROGBITS 0000000000401dc0 001dc0 00f1ba 00 AX 0 0 16
[14] .fini PROGBITS 0000000000410f7c 010f7c 000009 00 AX 0 0 4
... etc.
从上面的输出中，我们看到AWAVAUATUSH的所有实例都在.text节中(该节涵盖了文件的[0x1dc0, 0x10f7a)偏移量.
From above output, we see that all instances of AWAVAUATUSH are in .text section (which covers [0x1dc0, 0x10f7a) offsets of the file.
由于这是.text，我们希望在那里找到可执行指令.我们感兴趣的地址是0x401dc0(.text地址)+ 0x35e0(文件中AWAVAUATUSH的偏移量)-0x1dc0(文件中.text的偏移量)== 0x4035e0.
Since this is .text, we expect to find executable instructions there. The address we are interested in is 0x401dc0 (.text address) + 0x35e0 (offset of AWAVAUATUSH in the file) - 0x1dc0 (offset of .text in the file) == 0x4035e0.
首先，让我们检查一下上述算法是否正确:
First, let's check that the above arithmetic is correct:
gdb -q /bin/gzip
(gdb) x/s 0x4035e0
0x4035e0: "AWAVAUATUSH\203\354HdH\213\004%("
是的.接下来，那里的指示是什么?
Yes, it is. Next, what are the instructions there?
(gdb) x/20i 0x4035e0
0x4035e0: push %r15
0x4035e2: push %r14
0x4035e4: push %r13
0x4035e6: push %r12
0x4035e8: push %rbp
0x4035e9: push %rbx
0x4035ea: sub $0x48,%rsp
0x4035ee: mov %fs:0x28,%rax
0x4035f7: mov %rax,0x38(%rsp)
0x4035fc: xor %eax,%eax
0x4035fe: mov 0x213363(%rip),%rax # 0x616968
0x403605: mov %rdi,(%rsp)
0x403609: mov %rax,0x212cf0(%rip) # 0x616300
0x403610: cmpb $0x7a,(%rax)
0x403613: je 0x403730
0x403619: mov $0x616300,%ebx
0x40361e: mov (%rsp),%rdi
0x403622: callq 0x4019f0 <strlen@plt>
0x403627: cmp $0x20,%eax
0x40362a: mov %rax,0x8(%rsp)
这些确实看起来像普通的可执行指令. push %r15的操作码是什么? 此表显示0x41，0x57确实是push %r15，这些操作码只是 happen 在ASCII中拼写AW.同样，push %r14被编码为0x41，0x56，而这恰好是拼写AV.等等.
These indeed look like normal executable instructions. What is the opcode of push %r15? This table shows that 0x41, 0x57 is indeed push %r15, and these opcodes just happen to spell AW in ASCII. Similarly, push %r14 is encoded as 0x41, 0x56, which just happens spell AV. Etc.
P.S.我的gzip版本已被完全剥离，这就是为什么GDB在上述反汇编中未显示任何符号的原因.如果我改用非剥离版本，则会看到:
P.S. My version of gzip is fully stripped, which is why GDB shows no symbols in the above disassembly. If I use a non-stripped version instead, I see:
strings -o -tx gzip | grep AWAVAUATUSH | head -1
6be0 AWAVAUATUSH
readelf -WS gzip | grep text
[13] .text PROGBITS 0000000000401b00 001b00 00d102 00 AX 0 0 16
因此该字符串仍位于.text中.
So the string is still in .text.
gdb -q ./gzip
(gdb) p/a 0x0000000000401b00 + 0x6be0 - 0x001b00
$1 = 0x406be0 <inflate_dynamic>
(gdb) disas/r 0x406be0
Dump of assembler code for function inflate_dynamic:
0x0000000000406be0 <+0>: 41 57 push %r15
0x0000000000406be2 <+2>: 41 56 push %r14
0x0000000000406be4 <+4>: 41 55 push %r13
0x0000000000406be6 <+6>: 41 54 push %r12
0x0000000000406be8 <+8>: 55 push %rbp
0x0000000000406be9 <+9>: 53 push %rbx
0x0000000000406bea <+10>: 48 81 ec 38 05 00 00 sub $0x538,%rsp
...
现在您可以清楚地看到ASCII 0x4157415641554154...操作码序列.
Now you can clearly see the ASCII 0x4157415641554154... sequence of opcodes.
P.P.S.最初的问题询问有关AWAVAUATSH的问题，该问题确实出现在我的Mach-O bash和gzip中，但没有出现在Linux中.相反，AWAVAUATUSH不会出现在我的Mach-O二进制文件中.
P.P.S. The original question asks about AWAVAUATSH, which does appear in my Mach-O bash and gzip, but not in Linux ones. Conversely, AWAVAUATUSH does not appear in my Mach-O binaries.
答案是一样的. AWAVAUATSH序列与AWAVAUATUSH相同，但省略了push %rbp.
The answer is however the same. The AWAVAUATSH sequence is the same as AWAVAUATUSH, but with push %rbp omitted.
P.P.P.S以下是其他一些具有相同性质的有趣"字串:
P.P.P.S Here are some other "fun" strings of the same nature:
strings /bin/bash | grep '^A.A.A.' | sort | uniq -c | sort -nr | head
44 AWAVAUATUSH
27 AVAUATUSH
16 AWAVAUA
15 AVAUATUH
14 AWAVAUI
14 AWAVAUATUH
12 AWAVAUATI
8 AWAVAUE1
8 AVAUATI
6 AWAVAUATU
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