Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941896AbcKQSTy (ORCPT ); Thu, 17 Nov 2016 13:19:54 -0500 Received: from mail-yb0-f195.google.com ([209.85.213.195]:33263 "EHLO mail-yb0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S941831AbcKQSR7 (ORCPT ); Thu, 17 Nov 2016 13:17:59 -0500 From: Vince Weaver X-Google-Original-From: Vince Weaver Date: Thu, 17 Nov 2016 09:25:58 -0500 (EST) X-X-Sender: vince@macbook-air To: Josh Poimboeuf cc: Dmitry Vyukov , Peter Zijlstra , Vince Weaver , "linux-kernel@vger.kernel.org" , Ingo Molnar , Arnaldo Carvalho de Melo , "davej@codemonkey.org.uk" , Stephane Eranian Subject: Re: perf: fuzzer KASAN unwind_get_return_address In-Reply-To: <20161117140150.o6vy7bsrbjkg2nzd@treble> Message-ID: References: <20161115205748.xtroftp55igs55bz@treble> <20161116130337.GT3142@twins.programming.kicks-ass.net> <20161116143746.zoxdxrfqvmx35wln@treble> <20161116144943.GB3117@twins.programming.kicks-ass.net> <20161116145849.GR3157@twins.programming.kicks-ass.net> <20161117044828.vedc3whqkuki624r@treble> <20161117090446.GC3142@twins.programming.kicks-ass.net> <20161117091341.GS3157@twins.programming.kicks-ass.net> <20161117093028.GT3157@twins.programming.kicks-ass.net> <20161117140150.o6vy7bsrbjkg2nzd@treble> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1225 Lines: 28 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