copy and call function

Question

I'd like to copy and call a function, but the code below segfaults when calling the buffer. What do I have to change? (Linux, x86)

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

int foo () { return 12; }
void foo_end () {}

int main () {
  int s = (unsigned long long) foo_end - (unsigned long long) foo;
  int (*f) () = (int (*)()) malloc (s);
  memcpy ((void*) f, (const void*) foo, s);
  printf ("%d %d\n", f (), foo ());
}

EDIT: Working solution:

#include <string.h>
#include <malloc.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>

int foo () { return 12; }
void foo_end () {}

int main () {
  int s = (unsigned long long) foo_end - (unsigned long long) foo;
  int (*f) () = (int (*)()) malloc (s);
  memcpy ((void*) f, (const void*) foo, s);
  long ps = sysconf (_SC_PAGESIZE);
  void *fp = (void*) ((unsigned long long) f & ~((unsigned long long) (ps-1)));
  if (mprotect ((void*) fp, ps, PROT_READ | PROT_WRITE | PROT_EXEC)) return -1;
  printf ("%d %d\n", f (), foo ());
}

Answer 1

Potentially you're using an OS which does not grant execute permission to data segments.

Some environments will protect data pages against execution, to avoid various types of security problems (or exploits for them).

Consider calling mprotect() to enable execute for that page and report what happens.