ModifyFunctionPatch

Consider a simple C program:

examples/modify_function_patch/add.c

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main() {
    printf("2 + 3 = %d\n", add(2, 3));
    return 0;
}

After compiling and executing this program, the output is:

$ gcc -o add add.c && ./add
2 + 3 = 5

Now, we can use Patcherex2 to modify the add function to multiply the two arguments instead of adding them.

examples/modify_function_patch/patch.py

from patcherex2 import *

p = Patcherex("add")

new_add_func = """
int add(int a, int b) {
    return a * b;
}
"""

p.patches.append(ModifyFunctionPatch("add", new_add_func))

p.apply_patches()
p.binfmt_tool.save_binary("add_patched")

Executing the patched program yields a different result:

$ ./add_patched
2 + 3 = 6

💥 We've successfully modified the binary with Patcherex2!