Fix end_of_stack() fn and location of stack canary for archs using STACK_GROWSUP

Aaron Tomlin recently posted patches [1] to enable checking the stack canary on every task switch. Looking at the canary code, I realized that every arch (except ia64, which adds some space for register spill above the stack) shares a definition of end_of_stack() that makes it the first long after the threadinfo.

For stacks that grow down, this low address is correct because the stack starts at the end of the thread area and grows toward lower addresses. However, for stacks that grow up, toward higher addresses, this is wrong. (The stack actually grows away from the canary.) On these archs end_of_stack() should return the address of the last long, at the highest possible address for the stack.

[1] http://lkml.org/lkml/2014/9/12/293

---

Compile tested only, with Aaron's patches applied and the new option CONFIG_SCHED_STACK_END_CHECK they add enabled. I have no way to test this any further.

diff a/include/linux/sched.h b/include/linux/sched.h
@@ -2610,7 +2610,11 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
 
 static inline unsigned long *end_of_stack(struct task_struct *p)
 {
+#ifdef CONFIG_STACK_GROWSUP
+	return (unsigned long *)((unsigned long)task_thread_info(p) + THREAD_SIZE) - 1;
+#else
 	return (unsigned long *)(task_thread_info(p) + 1);
+#endif
 }
 
 #endif

Hi Chuck,

BUG: failure at kernel/sched/core.c:2664/schedule_debug()!
Kernel panic - not syncing: BUG!

OK.

Ingo,

I hope it's not too late to get this patch in (once the nit has been addressed) for CONFIG_STACK_GROWSUP?

Regards,

Aaron Tomlin