execute system command (bash) using assembly?

Question

Basically I am trying to execute the command /bin/ls using assembly, but unfortunately I am failing:

SECTION .data
    buf: db "Hello", 5
SECTION .text
global _start

_start:
    xor eax, eax
    mov edx, eax
    push edx
    mov eax, 0x736c2f2f     ; "sl/"
    push eax
    mov eax, 0x6e69622f     ; "nib/"
    push eax
    mov ebx, esp
    push edx
    mov eax, 0x2f
    push eax
    mov ecx, esp
    mov eax, 11
    xor edx, edx
    int 0x80

    mov eax, 1
    int 0x80

But If I change the mov eax, 11 to mov eax, 4 and add mov edx, 7 after xor edx, edx. It do print /bin/ls

Can anyone point the mistake I am making? Compiling the code with nasm -g -f elf -F dwarf ./shell.asm && ld -m elf_i386 -o shell shell.o and my arc is Linux kali 5.2.0-kali2-amd64 #1 SMP Debian 5.2.9-2kali1 (2019-08-22) x86_64 GNU/Linux

The filename argument goes into ebx not ecx. Use strace to see what you are doing. — Jester
– Jester, Commented Feb 5, 2020 at 20:21
@jester, updated my script, is it suppose to be that way now? still not working — Noobx
– Noobx, Commented Feb 5, 2020 at 20:53

Noobx · Accepted Answer · 2020-02-05 21:13:30Z

3

Found the problem, as pointed by @Jestor (thank you), I needed to store the executing file at ebx and all the arguments including the filename in ecx and set edx to null as below:

SECTION .data
buf: db "./", 0
SECTION .text
global _start

_start:
xor eax, eax
xor edx, edx
push eax
push long 0x736c2f2f    ; "sl/"
push long 0x6e69622f    ; "nib/"
mov ebx, esp
push eax
push byte 0x2f
mov esi, esp

push eax
push esi
push ebx
mov ecx, esp
mov eax, 0x0b
int 0x80

mov eax, 1
int 0x80

after my working shell, the ecx looked like below:

(gdb) x/50x $ecx
0xffffd370:     0xffffd384      0xffffd37c      0x00000000      0x0000002f
0xffffd380:     0x00000000      0x6e69622f      0x736c2f2f      0x00000000

answered Feb 5, 2020 at 21:13

Noobx

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