1

I have following code:

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

int main()
{
        int *ptr1 = malloc(16);
        int val1 = 0x12345678;
        printf("stack: %p\nheap: %p\n", &val1, ptr1);
        return 0;
}

Compilation: gcc -fpie -pie main.c

I wanted to test how aslr behaves under debugger, so i started gdb session, broke at main and ran the program. At main I show memory layout using 'info proc mappings': enter image description here

And those values should be randomized as far as i know due to aslr. But every time I re-run the program those values remains the same. I'm using Centos 8, x86_64. I also disabled built-in kernel ASLR by 'echo 0 > /proc/sys/kernel/randomize_va_space', but I don't think it matters.

I also checked if ALSR is enabled using checksec: enter image description here

Is it normal behavior or am I missing something?

EDIT: I saw that when I run binary without gdb everything works totally fine. What can I do to make it work under debugger?

qwertyuiqwertyui
  • 11
  • 2

1 Answers1

2

To make debugging easier, GDB turns off ASLR by default. To turn it back on, do set disable-randomization off before you start running the program being debugged. See https://sourceware.org/gdb/onlinedocs/gdb/Starting.html for more details.

Joseph Sible-Reinstate Monica
  • 7,110
  • 3
  • 21
  • 35