x86_64

Difference between x86 & x86_64

The first major difference is the size of memory address. No surprise here :) So memory addresses are 64 bits long, but user space only uses the first 47 bits; keep this in mind because if you specified an address greater than 0x00007fffffffffff, you'll raise an exception.

So that means that 0x4141414141414141 will raise exception, but the address 0x0000414141414141 is safe.

I think this is the tricky part while you're fuzzing or developing your exploit. In fact there are tons of others differences, but for the purpose of this paper, it’s not important to know all of them.

Vulnerable code snippet

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

int main(int argc, char **argv) {
    char buffer[256];
    if(argc != 2) {
        exit(0);
    }
    printf("%p\n", buffer);
    strcpy(buffer, argv[1]);
    printf("%s\n", buffer);
    
    return 0;
}

I decide to print the buffer pointer address to save time through the exploit development.

You can compile this code using gcc:

gcc -m64 bof.c -o bof -z execstack -fno-stack-protector

Trigger the overflow