1

How can i hook functions with frida? Can someone give me an example please, for something that do that?

Hook at 0x412312 and change the assembly code to "mov eax, 999"

I Arleady tried something like: https://pastebin.com/eGPf5k0R

but it doesn't work for me, thx for helping!

  • 1
    What do you want to achieve exactly? If you want to just patch 1 instruction, use Memory.patchCode or Memory.writeByteArray to write this instruction or its raw representation. – sudhackar Oct 12 '19 at 13:20
2

Try using Memory.patchCode to achieve this. Here's a short example.

int test() { return 1024; }

int main(int argc, char **argv) {
    printf("%d\n", test());
    return 0;
}

When compiled this looks like

[0x00400560]> s sym.test
[0x00400656]> pdf
┌ (fcn) sym.test 11
│   sym.test ();
│           ; CALL XREF from main @ 0x400670
│           0x00400656      55             push rbp
│           0x00400657      4889e5         mov rbp, rsp
│           0x0040065a      b800040000     mov eax, 0x400              ; 1024
│           0x0040065f      5d             pop rbp
└           0x00400660      c3             ret
[0x00400656]> s sym.main
[0x00400661]> pdf
┌ (fcn) main 44
│   int main (int argc, char **argv, char **envp);
│           ; var char **var_10h @ rbp-0x10
│           ; var int32_t var_4h @ rbp-0x4
│           ; arg int argc @ rdi
│           ; arg char **argv @ rsi
│           ; DATA XREF from entry0 @ 0x40057d
│           0x00400661      55             push rbp
│           0x00400662      4889e5         mov rbp, rsp
│           0x00400665      4883ec10       sub rsp, 0x10
│           0x00400669      897dfc         mov dword [var_4h], edi     ; argc
│           0x0040066c      488975f0       mov qword [var_10h], rsi    ; argv
│           0x00400670      e8e1ffffff     call sym test()             ; sym.test
│           0x00400675      89c6           mov esi, eax
│           0x00400677      bf24084000     mov edi, 0x400824           ; const char *format
│           0x0040067c      b800000000     mov eax, 0
│           0x00400681      e89afeffff     call sym.imp.printf         ; int printf(const char *format)
│           0x00400686      b800000000     mov eax, 0
│           0x0040068b      c9             leave
└           0x0040068c      c3             ret

At 0x0040065a, the constant 1024(0x400) is copied to eax. When run this looks like

$ ./test
1024

This can be patched at runtime by frida using patchCode

var pc = new NativePointer(0x0040065a)
Memory.patchCode(pc, 5, function (code) {
  var cw = new X86Writer(code, { pc: pc });
  cw.putMovRegU32('eax', 999);
  cw.flush();
});

When run

$ frida -q -l patch_code.js -f ./test --no-pause
Spawned `./test`. Resuming main thread!                                  
999
Process terminated
| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.