Stack Alignment

스택 정렬(Stack Alignment)은 스택을 16바이트 경계에 정렬하는 것을 의미한다.

32bit binary에서 정렬 코드

gdb-peda$ pd main
Dump of assembler code for function main:
   0x080485d3 <+0>:     lea    ecx,[esp+0x4]			// Stack Alignment
   0x080485d7 <+4>:     and    esp,0xfffffff0			// 하위 1비트 -> 0
   0x080485da <+7>:     push   DWORD PTR [ecx-0x4]		// ret
   0x080485dd <+10>:    push   ebp				// sfp
   0x080485de <+11>:    mov    ebp,esp
   0x080485e0 <+13>:    push   ecx
   0x080485e1 <+14>:    sub    esp,0x4
   0x080485e4 <+17>:    mov    eax,ecx
   0x080485e6 <+19>:    cmp    DWORD PTR [eax],0x1
   0x080485e9 <+22>:    jg     0x8048605 <main+50>
   0x080485eb <+24>:    sub    esp,0xc
   0x080485ee <+27>:    push   0x80486e4
   0x080485f3 <+32>:    call   0x8048430 <puts@plt>
   0x080485f8 <+37>:    add    esp,0x10
   0x080485fb <+40>:    sub    esp,0xc
   0x080485fe <+43>:    push   0x0
   0x08048600 <+45>:    call   0x8048450 <exit@plt>
   0x08048605 <+50>:    call   0x804857b <vuln>
   0x0804860a <+55>:    nop
   0x0804860b <+56>:    mov    ecx,DWORD PTR [ebp-0x4]
   0x0804860e <+59>:    leave
   0x0804860f <+60>:    lea    esp,[ecx-0x4]
   0x08048612 <+63>:    ret
End of assembler dump.
gdb-peda$

 

---

참고문헌

https://stackoverflow.com/questions/672461/what-is-stack-alignment

what is "stack alignment"?

https://www.lazenca.net/display/TEC/01.Frame+Pointer+Overwrite%28One-byte+Overflow%29+-+x86

01.Frame Pointer Overwrite(One-byte Overflow) - x86 - TechNote - Lazenca.0x0