From: Vince Weaver <vincent.weaver@maine.edu>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Vince Weaver <vincent.weaver@maine.edu>,
Peter Zijlstra <peterz@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
"davej@codemonkey.org.uk" <davej@codemonkey.org.uk>,
Stephane Eranian <eranian@gmail.com>
Subject: Re: perf: fuzzer KASAN unwind_get_return_address
Date: Thu, 17 Nov 2016 12:15:54 -0500 (EST) [thread overview]
Message-ID: <alpine.DEB.2.20.1611171213310.11652@macbook-air> (raw)
In-Reply-To: <CACT4Y+ZRCnnB0G=eF-oCqZQ1EiCgFTCdYXdbM07ZztHcqFnoLA@mail.gmail.com>
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
next prev parent reply other threads:[~2016-11-17 17:16 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-15 17:43 perf: fuzzer KASAN unwind_get_return_address Vince Weaver
2016-11-15 18:57 ` Peter Zijlstra
2016-11-15 19:04 ` Dmitry Vyukov
2016-11-15 20:56 ` Josh Poimboeuf
2016-11-15 19:05 ` Vince Weaver
2016-11-15 20:57 ` Josh Poimboeuf
2016-11-16 13:03 ` Peter Zijlstra
2016-11-16 13:18 ` Dmitry Vyukov
2016-11-16 14:37 ` Josh Poimboeuf
2016-11-16 14:49 ` Peter Zijlstra
2016-11-16 14:58 ` Josh Poimboeuf
2016-11-16 14:58 ` Peter Zijlstra
2016-11-17 4:48 ` Josh Poimboeuf
2016-11-17 9:04 ` Peter Zijlstra
2016-11-17 9:13 ` Peter Zijlstra
2016-11-17 9:30 ` Peter Zijlstra
2016-11-17 9:48 ` Dmitry Vyukov
2016-11-17 14:01 ` Josh Poimboeuf
2016-11-17 14:25 ` Vince Weaver
2016-11-17 14:36 ` Josh Poimboeuf
2016-11-17 14:58 ` Dmitry Vyukov
2016-11-17 17:15 ` Vince Weaver [this message]
2016-11-17 15:18 ` Josh Poimboeuf
2016-11-17 16:07 ` Peter Zijlstra
2016-11-17 17:17 ` Peter Zijlstra
2016-11-22 12:30 ` [tip:perf/urgent] perf/x86/intel: Cure bogus unwind from PEBS entries tip-bot for Peter Zijlstra
2016-11-16 15:06 ` perf: fuzzer KASAN unwind_get_return_address Vince Weaver
2016-11-17 15:57 ` [PATCH 1/2] unwind: prevent KASAN false positive warnings in guess unwinder Josh Poimboeuf
2016-11-17 15:57 ` [PATCH 2/2] dumpstack: prevent KASAN false positive warnings Josh Poimboeuf
2016-11-18 9:04 ` [tip:x86/urgent] x86/dumpstack: Prevent " tip-bot for Josh Poimboeuf
2016-11-17 20:26 ` [PATCH 1/2] unwind: prevent KASAN false positive warnings in guess unwinder Josh Poimboeuf
2016-11-18 8:38 ` Ingo Molnar
2016-11-18 9:04 ` [tip:x86/urgent] x86/unwind: Prevent " tip-bot for Josh Poimboeuf
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