Messages in this thread | | | From | Vince Weaver <> | Date | Thu, 17 Nov 2016 12:15:54 -0500 (EST) | Subject | Re: perf: fuzzer KASAN unwind_get_return_address |
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On Thu, 17 Nov 2016, Dmitry Vyukov wrote:
> On Thu, Nov 17, 2016 at 3:36 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > On Thu, Nov 17, 2016 at 09:25:58AM -0500, Vince Weaver wrote: > >> 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. > > > > I believe KASAN only works with gcc 5 and later, so that would explain > > why you aren't seeing it with gcc 4.9. > > Right. 4.9 has limited support for KASAN. It supports general > instrumentation, but only with CONFIG_KASAN_OUTLINE, and it does not > support stack poisoning. Which is required to detect stack OOBs.
I guess it's time to update the other machines to debian-unstable then. I didn't really need to be able to run dmesg as non-root anyway.
I would actually be compiling the kernels with gcc-6.2 rather than gcc-5 but that seems to not work currently. Haven't had time to see if that's a known issue or not.
Vince
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