Exec-shield can't be disabled?

[btopia]

Hi,

I'm running Fedora 14 x86_64.

I have

#cat /proc/sys/kernel/exec-shield
0
#cat /proc/sys/kernel/randomize_va_space
0


However, when I attempted to run the following piece of code, I still got a segmentation fault right at the first instruction after branching onto the address of buf (*fn).

I thought when we have /proc/sys/kernel/exec-shield = 0, then it should be allowed to execute code on the stack?

--------------------------------------------------------------------------


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

unsigned char shellcode[]="\xb0\x01\x31\xdb\xcd\x80";

int main()
{
char buf[512];

typedef void (*pfn)();

memcpy(buf, shellcode, 512);

pfn fn = (pfn)buf;

(*fn)(); /// Segmentation fault !

return 0;
}

-----------------------------------------------------------------

Following is the GDB output

(gdb) run
Starting program: /home/kat/t/a.out

Program received signal SIGSEGV, Segmentation fault.
0x00007fffffffdfe0 in ?? ()
Missing separate debuginfos, use: debuginfo-install glibc-2.12.1-3.x86_64 libgcc-4.4.4-10.fc13.x86_64 libstdc++-4.4.4-10.fc13.x86_64
(gdb) x/5i 0x7fffffffdfe0
=> 0x7fffffffdfe0: mov $0x1,%al
0x7fffffffdfe2: xor %ebx,%ebx
0x7fffffffdfe4: int $0x80
0x7fffffffdfe6: add %al,(%rax)
0x7fffffffdfe8: add %al,(%rax)
(gdb)