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

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 <>
parent 1ff56830
......@@ -129,15 +129,19 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
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)
ebp = *(unsigned long *)ebp;
ebp = new_ebp;
while (valid_stack_ptr(tinfo, stack)) {
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