Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 808dbbb6 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

x86: be more careful when walking back the frame pointer chain 



When showing the stack backtrace, make sure that we never accept not
only an unchanging frame pointer, but also a frame pointer that moves
back down the stack frame.  It must always grow up (toward older stack
frames).

I doubt this has triggered, but a subtly corrupt stack with extremely
unlucky contents could cause us to loop forever on a bogus endless frame
pointer chain.

This review was triggered by much worse problems happening in some of
the other stack unwinding code.

Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1ff56830

arch/i386/kernel/traps.c

+7 −3
Original line number Diff line number Diff line
@@ -129,15 +129,19 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo, 


#ifdef	CONFIG_FRAME_POINTER

	while (valid_stack_ptr(tinfo, (void *)ebp)) {

		unsigned long new_ebp;

		addr = *(unsigned long *)(ebp + 4);

		ops->address(data, addr);

		/*

		 * break out of recursive entries (such as

		 * end_of_stack_stop_unwind_function):

		 * end_of_stack_stop_unwind_function). Also,

		 * we can never allow a frame pointer to

		 * move downwards!

	 	 */

		if (ebp == *(unsigned long *)ebp)

	 	new_ebp = *(unsigned long *)ebp;

		if (new_ebp <= ebp)

			break;

		ebp = *(unsigned long *)ebp;

		ebp = new_ebp;

	}

#else

	while (valid_stack_ptr(tinfo, stack)) {