Re: perf: fuzzer KASAN unwind_get_return_address

From: Josh Poimboeuf
Date: Thu Nov 17 2016 - 12:39:40 EST

On Thu, Nov 17, 2016 at 10:48:27AM +0100, Dmitry Vyukov wrote:
> Just in case, there is currently a known KASAN false positive related
> to longjmp's on GPFs. When a syscall hits GPF stack is unwound to
> kernel entry point, this leaves a bunch of stray poisoned redzones on
> the thread stack. They later cause false stack-out-of-bounds reports.
> But this does not seem to be the case here. Kernel is not tainted. And
> shadow at the bottom of the reports looks sane.
> But if that's the case somehow, we will need to add
> kasan_unpoison_remaining_stack() call before a longjmp like we did for
> jprobe_return():

I'm pretty sure this isn't a KASAN false positive. The unwinder does
actually seem to be accessing a bad area of the stack, in the middle of
a function's stack frame.