cgdbeip

Control eip/rip register via user input

I have the exercise to control the input of the eip/rip register (in my case rip) arbitrarily. The following program is given:

#include <stdio.h>
#include <string.h>

#define VAR_SIZE 32

void output(int argc, char** argv) {
    char stack[VAR_SIZE];
    strcpy(stack, argv[1]);
    printf("%s\n", stack);
}

int main(int argc, char** argv) {
    output(argc, argv);
    return 0;
}

We may use the debugger gdb. Unfortunately I have no idea where to start.

Solution

  • In order to set the value of the RIP x86-64 register, you can use the following command in gdb:

    set $rip = 20

    This will set the value of the register to 20.