Re: perf: fuzzer KASAN unwind_get_return_address

[Vince Weaver]

On Thu, 17 Nov 2016, Josh Poimboeuf wrote:

> 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():
> > https://groups.google.com/d/msg/kasan-dev/Hzox58yZ4MU/TOdFoWMuBQAJ
> 
> 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.

I'm having trouble reproducing it on a few other machines I have fuzzing.
So there might be some kernel option contributing, I need to compare 
.configs.

Also the machine that easily triggers the problem I'm compiling with 
gcc-5.4 where the machines I can't are using gcc-4.9.

Vince