Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030481AbbD1OVj (ORCPT ); Tue, 28 Apr 2015 10:21:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37600 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965825AbbD1OVh (ORCPT ); Tue, 28 Apr 2015 10:21:37 -0400 Date: Tue, 28 Apr 2015 09:21:05 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Michal Marek , x86@kernel.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] x86, stackvalidate: Compile-time stack frame pointer validation Message-ID: <20150428142105.GB17315@treble.redhat.com> References: <0c54981fcba75d6a32ad4074786b99bbf0fc0810.1430142416.git.jpoimboe@redhat.com> <20150428121606.GX23123@twins.programming.kicks-ass.net> <20150428140454.GA17315@treble.redhat.com> <20150428140842.GC23123@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150428140842.GC23123@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2101 Lines: 41 On Tue, Apr 28, 2015 at 04:08:42PM +0200, Peter Zijlstra wrote: > On Tue, Apr 28, 2015 at 09:04:54AM -0500, Josh Poimboeuf wrote: > > On Tue, Apr 28, 2015 at 02:16:06PM +0200, Peter Zijlstra wrote: > > > On Mon, Apr 27, 2015 at 08:56:27AM -0500, Josh Poimboeuf wrote: > > > > Frame pointer based stack traces aren't always reliable. One big reason > > > > is that most asm functions don't set up the frame pointer. > > > > > > > > Fix that by enforcing that all asm functions honor CONFIG_FRAME_POINTER. > > > > This is done with a new stackvalidate host tool which is automatically > > > > run for every compiled .S file and which validates that every asm > > > > function does the proper frame pointer setup. > > > > > > Would it make sense (maybe as an additional CONFIG_*_DEBUG thing) to > > > also process the output of GCC with this tool? To both double check GCC > > > and to give the tool more input? > > > > I tried that, but I discovered that gcc's usage of frame pointers would > > be a lot harder to validate. It only sets up the frame pointer in code > > paths which have call instructions. There are a lot of functions which > > have conditional jumps at the beginning which can jump straight to a > > return instruction without first doing the frame pointer setup. > > Hmm, would not such code break your patching? No, because we'll also do some runtime stack validation (which will be a future patch set). If we detect preemption or an irq frame on the stack, we'll assume the stack is unreliable and delay the patching of the task (*). Otherwise the stack will only consist of calls down to schedule() which will be guaranteed to have frame pointers. (*) This can be even further improved by making _all_ stacks reliable if we can ensure that dwarf call frame information is reliable (more future patch sets). -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/