Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933341AbcKPOtu (ORCPT ); Wed, 16 Nov 2016 09:49:50 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:60316 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933202AbcKPOtt (ORCPT ); Wed, 16 Nov 2016 09:49:49 -0500 Date: Wed, 16 Nov 2016 15:49:43 +0100 From: Peter Zijlstra To: Josh Poimboeuf Cc: Vince Weaver , "linux-kernel@vger.kernel.org" , Ingo Molnar , Arnaldo Carvalho de Melo , "davej@codemonkey.org.uk" , "dvyukov@google.com" , Stephane Eranian Subject: Re: perf: fuzzer KASAN unwind_get_return_address Message-ID: <20161116144943.GB3117@twins.programming.kicks-ass.net> References: <20161115185756.GL3142@twins.programming.kicks-ass.net> <20161115205748.xtroftp55igs55bz@treble> <20161116130337.GT3142@twins.programming.kicks-ass.net> <20161116143746.zoxdxrfqvmx35wln@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161116143746.zoxdxrfqvmx35wln@treble> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1275 Lines: 29 On Wed, Nov 16, 2016 at 08:37:46AM -0600, Josh Poimboeuf wrote: > On Wed, Nov 16, 2016 at 02:03:37PM +0100, Peter Zijlstra wrote: > > On Tue, Nov 15, 2016 at 02:57:48PM -0600, Josh Poimboeuf wrote: > > > Would you mind posting a disassembly of unwind_get_return_address()? > > > Any idea how recreatable it is? (In particular I'd be interested in > > > seeing this dump with the latest unwinder improvements in the -tip tree, > > > which dump the pt_regs associated with an interrupt.) > > > > Fairly reproducable it seems, doesn't seem to include pt_regs dumps > > though :/ > > > > tip/master as of this morning. > > Thanks. This is actually a different issue than the one reported by > Vince. In this case FRAME_POINTER is disabled, so it uses the "guess" > unwinder which scans every address on the stack, looking for text > addresses. So the kasan errors are expected. > > (The missing pt_regs are also expected: the guess unwinder doesn't show > them.) > > I'll work up a patch to fix this. I still have no idea what's causing > Vince's bug in the frame pointer unwinder. Hurm,.. by the number of '?' entries in Vince's backtrace I was assuming it was without frame pointers. Let me enable those and run again, it didn't insta-trigger like it does without.