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 Signed-off-by: Chuck Ebbert <cebbert.l...@gmail.com> Tested-by: James Hogan <james.ho...@imgtec.com> [metag] Acked-by: James Hogan <james.ho...@imgtec.com> Acked-by: Aaron Tomlin <atom...@redhat.com> --- V3: Fix line length, add comment. diff a/include/linux/sched.h b/include/linux/sched.h --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2609,9 +2609,23 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct task_thread_info(p)->task = p; } +/* + * Return the address of the last usable long on the stack. + * + * When the stack grows down, this is just above the thread + * info struct. Going any lower will corrupt the threadinfo. + * + * When the stack grows up, this is the highest address. + * Beyond that position, we corrupt data on the next page. + */ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
