Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754963AbbFLQA5 (ORCPT ); Fri, 12 Jun 2015 12:00:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43690 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750803AbbFLQA4 (ORCPT ); Fri, 12 Jun 2015 12:00:56 -0400 Message-ID: <557B0232.50108@redhat.com> Date: Fri, 12 Jun 2015 17:00:50 +0100 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Josh Poimboeuf CC: Ingo Molnar , Andy Lutomirski , Michal Marek , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "linux-kernel@vger.kernel.org" , Andi Kleen , live-patching@vger.kernel.org, X86 ML , "H. Peter Anvin" , Linus Torvalds , Peter Zijlstra Subject: Re: [PATCH v5 02/10] x86: Compile-time asm code validation References: <20150610175320.GD29724@treble.redhat.com> <20150610185845.GA1125@treble.redhat.com> <20150611061050.GB30720@gmail.com> <20150611141000.GC11517@treble.redhat.com> <557ABFF8.5040304@redhat.com> <20150612141030.GA18807@treble.hsd1.ky.comcast.net> In-Reply-To: <20150612141030.GA18807@treble.hsd1.ky.comcast.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2143 Lines: 48 On 06/12/2015 03:10 PM, Josh Poimboeuf wrote: > On Fri, Jun 12, 2015 at 12:18:16PM +0100, Pedro Alves wrote: >> On 06/11/2015 03:10 PM, Josh Poimboeuf wrote: >> >>> C would definitely make more sense when analyzing object code. In fact, >>> asmvalidate is written in C. But then I guess we'd have to re-implement >>> the .cfi stuff and populate the DWARF sections manually instead of >>> letting the assembler do it. >> >> Was doing all this directly in the assembler considered? That is, >> e.g., add some knob that makes it error/warn in the same conditions >> you're making the validator catch. For tail calls, you'd e.g., add >> some new ".nonlocal" directive that you'd use to whitelist the >> following jump. And then if it's possible run a CFI generator >> as a separate step over the source, it sounds like it should also >> be possible to have the assembler do it instead too (again with >> some new high level directive to trigger/help it). > > In general I think doing these types of things in the assembler would be > a good idea. Missing or inaccurate debug data for asm code seems to be > a common problem for other projects as well. As Andy pointed out, > they're doing similar things in musl [1]. Thanks for the pointer. > So it might be useful to add > an option to the assembler which validates that the code conforms to > certain structural rules, and then inserts frame pointer and/or .cfi > directives. > That said, the kernel has much more custom features than other projects. > There are some sneaky macros, like _ASM_EXTABLE and ALTERNATIVE, which > hide code in various sections. Unless we're able to somehow either stop > using these macros or isolate them to a few places, I doubt that such a > general purpose assembler option would work. How does the asmvalidator handle these? > [1] http://www.openwall.com/lists/musl/2015/05/31/5 Thanks, Pedro Alves -- 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/