Stack Smashing Protector

GCC Stack-Smashing Protector (ProPolice)

What is it?

The GCC SSP protects the stack from buffer overflows. If a buffer overflow occurs, you're informed instantly.

How to implement it?

When you started with OS developing, you might have seen that following error:

... undefined reference to __stack_chk_fail

... undefined reference to __stack_chk_guard

That's the SSP! You probably just didn't care about it and disabled it.

Now, implementing this feature is dead easy and it is a really handy thing.

   void * __stack_chk_guard = NULL;

   void __stack_chk_guard_setup()
   {
       unsigned char * p;
       p = (unsigned char *) &__stack_chk_guard;
       p[sizeof(__stack_chk_guard)-1] = 255;  /* <- this should be probably randomized */
       p[sizeof(__stack_chk_guard)-2] = '\n';
       p[0] = 0;
   }

   void __sttribute__((noreturn)) __stack_chk_fail()
   { /* put you're panic or whatever in here */
       unsigned char * vid = (unsigned char *)0xB8000;
       vid[1] = 7;
       for(;;)
       vid[0]++;
   }

Call __stack_chk_guard_setup at early boot stage, from there on you're protected from most buffer overflows.

Don't forget to add -fstack-protector-all to the gcc flags.