stackprotector: Increase the per-task stack canary's random range from 32 bits to 64 bits on 64-bit platforms

The stack canary is an 'unsigned long' and should be fully initialized to
random data rather than only 32 bits of random data.

Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Arjan van Ven <arjan@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-hardening@lists.openwall.com
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170504133209.3053-1-danielmicay@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/fork.c

@@ -536,7 +536,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	set_task_stack_end_magic(tsk);
 
 #ifdef CONFIG_CC_STACKPROTECTOR
-	tsk->stack_canary = get_random_int();
+	tsk->stack_canary = get_random_long();
 #endif
 
 	/*