为什么在GDB上出现断点问题? GDB停止 [英] Why do i have this problem with breakpoints on GDB? GDB Stops
问题描述
当尝试调用函数 strcpy()时，我试图在GDB上设置一个断点，但是GDB停止了，我不知道如何找到错误，这对GDB和我想研究二进制剥削，因此我正在阅读的论坛对此没有任何解释，这里是输出；
(gdb) disassemble main
Dump of assembler code for function main:
0x00000000000011c9 <+0>: endbr64
0x00000000000011cd <+4>: push rbp
0x00000000000011ce <+5>: mov rbp,rsp
0x00000000000011d1 <+8>: sub rsp,0x50
0x00000000000011d5 <+12>: mov DWORD PTR [rbp-0x44],edi
0x00000000000011d8 <+15>: mov QWORD PTR [rbp-0x50],rsi
0x00000000000011dc <+19>: mov rax,QWORD PTR fs:0x28
0x00000000000011e5 <+28>: mov QWORD PTR [rbp-0x8],rax
0x00000000000011e9 <+32>: xor eax,eax
0x00000000000011eb <+34>: cmp DWORD PTR [rbp-0x44],0x1
0x00000000000011ef <+38>: jne 0x1207 <main+62>
0x00000000000011f1 <+40>: lea rsi,[rip+0xe10] # 0x2008
0x00000000000011f8 <+47>: mov edi,0x1
0x00000000000011fd <+52>: mov eax,0x0
0x0000000000001202 <+57>: call 0x10c0 <errx@plt>
0x0000000000001207 <+62>: mov DWORD PTR [rbp-0x34],0x0
0x000000000000120e <+69>: mov rax,QWORD PTR [rbp-0x50]
0x0000000000001212 <+73>: add rax,0x8
0x0000000000001216 <+77>: mov rdx,QWORD PTR [rax]
0x0000000000001219 <+80>: lea rax,[rbp-0x30]
0x000000000000121d <+84>: mov rsi,rdx
0x0000000000001220 <+87>: mov rdi,rax
0x0000000000001223 <+90>: call 0x1090 <strcpy@plt> // breakpoint here
0x0000000000001228 <+95>: mov eax,DWORD PTR [rbp-0x34]
0x000000000000122b <+98>: test eax,eax
0x000000000000122d <+100>: je 0x1247 <main+126>
0x000000000000122f <+102>: mov eax,DWORD PTR [rbp-0x34]
0x0000000000001232 <+105>: mov esi,eax
0x0000000000001234 <+107>: lea rdi,[rip+0xde5] # 0x2020
0x000000000000123b <+114>: mov eax,0x0
0x0000000000001240 <+119>: call 0x10d0 <printf@plt>
0x0000000000001245 <+124>: jmp 0x1253 <main+138>
0x0000000000001247 <+126>: lea rdi,[rip+0xe12] # 0x2060
0x000000000000124e <+133>: call 0x10a0 <puts@plt>
0x0000000000001253 <+138>: mov eax,0x0
0x0000000000001258 <+143>: mov rcx,QWORD PTR [rbp-0x8]
0x000000000000125c <+147>: xor rcx,QWORD PTR fs:0x28
0x0000000000001265 <+156>: je 0x126c <main+163>
0x0000000000001267 <+158>: call 0x10b0 <__stack_chk_fail@plt>
0x000000000000126c <+163>: leave
0x000000000000126d <+164>: ret
End of assembler dump.
(gdb) break *0x0000000000001223 // I want to set the breakpoint here
Breakpoint 1 at 0x1223
(gdb) r AAAA // I try to run the program providing arguments
Starting program: /home/ryan/liveoverflow_youtube/0x05_simple_crackme_intro_assembler/stackReg AAAA
[1]+ Stopped gdb stackReg // This is the problem?
GDB停止是一个错误，当GDB在尝试放置断点时引发错误时，就会发生此错误，此错误已通过以下补丁在上游GDB中修复:
https://sourceware.org/ml/gdb-patches/2019-05/msg00361.html
一旦看到GDB这样停止:
[1]+ Stopped
您应该放回外壳.只需使用fg命令恢复GDB，然后继续进行调试会话. GDB 9发布后，此错误将得到修复.
正如评论中指出的那样，断点地址不正确的原因是您使用的是位置独立可执行文件(PIE)，该代码将在流程启动时重新定位.
使用starti启动GDB，然后您可以反汇编main并查看代码的实际放置位置.
I tried to set a break-point on GDB when a function strcpy() is called, but GDB stops, and i don't know how to find the error, im new to GDB and i want to study binary exploitation, so the forum i'm reading does not explain nothing about this, here is the output;
(gdb) disassemble main
Dump of assembler code for function main:
0x00000000000011c9 <+0>: endbr64
0x00000000000011cd <+4>: push rbp
0x00000000000011ce <+5>: mov rbp,rsp
0x00000000000011d1 <+8>: sub rsp,0x50
0x00000000000011d5 <+12>: mov DWORD PTR [rbp-0x44],edi
0x00000000000011d8 <+15>: mov QWORD PTR [rbp-0x50],rsi
0x00000000000011dc <+19>: mov rax,QWORD PTR fs:0x28
0x00000000000011e5 <+28>: mov QWORD PTR [rbp-0x8],rax
0x00000000000011e9 <+32>: xor eax,eax
0x00000000000011eb <+34>: cmp DWORD PTR [rbp-0x44],0x1
0x00000000000011ef <+38>: jne 0x1207 <main+62>
0x00000000000011f1 <+40>: lea rsi,[rip+0xe10] # 0x2008
0x00000000000011f8 <+47>: mov edi,0x1
0x00000000000011fd <+52>: mov eax,0x0
0x0000000000001202 <+57>: call 0x10c0 <errx@plt>
0x0000000000001207 <+62>: mov DWORD PTR [rbp-0x34],0x0
0x000000000000120e <+69>: mov rax,QWORD PTR [rbp-0x50]
0x0000000000001212 <+73>: add rax,0x8
0x0000000000001216 <+77>: mov rdx,QWORD PTR [rax]
0x0000000000001219 <+80>: lea rax,[rbp-0x30]
0x000000000000121d <+84>: mov rsi,rdx
0x0000000000001220 <+87>: mov rdi,rax
0x0000000000001223 <+90>: call 0x1090 <strcpy@plt> // breakpoint here
0x0000000000001228 <+95>: mov eax,DWORD PTR [rbp-0x34]
0x000000000000122b <+98>: test eax,eax
0x000000000000122d <+100>: je 0x1247 <main+126>
0x000000000000122f <+102>: mov eax,DWORD PTR [rbp-0x34]
0x0000000000001232 <+105>: mov esi,eax
0x0000000000001234 <+107>: lea rdi,[rip+0xde5] # 0x2020
0x000000000000123b <+114>: mov eax,0x0
0x0000000000001240 <+119>: call 0x10d0 <printf@plt>
0x0000000000001245 <+124>: jmp 0x1253 <main+138>
0x0000000000001247 <+126>: lea rdi,[rip+0xe12] # 0x2060
0x000000000000124e <+133>: call 0x10a0 <puts@plt>
0x0000000000001253 <+138>: mov eax,0x0
0x0000000000001258 <+143>: mov rcx,QWORD PTR [rbp-0x8]
0x000000000000125c <+147>: xor rcx,QWORD PTR fs:0x28
0x0000000000001265 <+156>: je 0x126c <main+163>
0x0000000000001267 <+158>: call 0x10b0 <__stack_chk_fail@plt>
0x000000000000126c <+163>: leave
0x000000000000126d <+164>: ret
End of assembler dump.
(gdb) break *0x0000000000001223 // I want to set the breakpoint here
Breakpoint 1 at 0x1223
(gdb) r AAAA // I try to run the program providing arguments
Starting program: /home/ryan/liveoverflow_youtube/0x05_simple_crackme_intro_assembler/stackReg AAAA
[1]+ Stopped gdb stackReg // This is the problem?
GDB stopping like this is a bug which occurs when GDB throws an error while trying to place a breakpoint, it was fixed in upstream GDB with this patch:
https://sourceware.org/ml/gdb-patches/2019-05/msg00361.html
Once you see GDB stopped like this:
[1]+ Stopped
you should be dropped back to a shell. Just resume GDB with the fg command and continue your debug session. Once GDB 9 is out this bug will be fixed.
As was pointed out in a comment the reason the breakpoint address is incorrect is that you are using a Position Independent Executable (PIE), the code will be relocated when the process starts.
Start GDB with starti, then you can disassemble main and see where the code has actually been placed.
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