lkml.org 
[lkml]   [2016]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: perf: fuzzer KASAN unwind_get_return_address
    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

    \
     
     \ /
      Last update: 2016-11-17 18:17    [W:5.864 / U:0.728 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site