From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1F6DEC41514 for ; Wed, 4 Sep 2019 08:49:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 011B92339D for ; Wed, 4 Sep 2019 08:49:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729220AbfIDIte (ORCPT ); Wed, 4 Sep 2019 04:49:34 -0400 Received: from mx2.suse.de ([195.135.220.15]:57098 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726240AbfIDIte (ORCPT ); Wed, 4 Sep 2019 04:49:34 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 4592CADFE; Wed, 4 Sep 2019 08:49:33 +0000 (UTC) Date: Wed, 4 Sep 2019 10:49:32 +0200 From: Petr Mladek To: Miroslav Benes Cc: Joe Lawrence , jikos@kernel.org, Josh Poimboeuf , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [RFC PATCH 2/2] livepatch: Clear relocation targets on a module removal Message-ID: <20190904084932.gndrtewubqiaxmzy@pathway.suse.cz> References: <20190728200427.dbrojgu7hafphia7@treble> <20190814151244.5xoaxib5iya2qjco@treble> <20190816094608.3p2z73oxcoqavnm4@pathway.suse.cz> <20190822223649.ptg6e7qyvosrljqx@treble> <20190823081306.kbkm7b4deqrare2v@pathway.suse.cz> <20190826145449.wyo7avwpqyriem46@treble> <5c649320-a9bf-ae7f-5102-483bc34d219f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170912 (1.9.0) Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Tue 2019-09-03 15:02:34, Miroslav Benes wrote: > On Mon, 2 Sep 2019, Joe Lawrence wrote: > > > On 9/2/19 12:13 PM, Miroslav Benes wrote: > > >> I can easily foresee more problems like those in the future. Going > > >> forward we have to always keep track of which special sections are > > >> needed for which architectures. Those special sections can change over > > >> time, or can simply be overlooked for a given architecture. It's > > >> fragile. > > > > > > Indeed. It bothers me a lot. Even x86 "port" is not feature complete in > > > this regard (jump labels, alternatives,...) and who knows what lurks in > > > the corners of the other architectures we support. > > > > > > So it is in itself reason enough to do something about late module > > > patching. > > > > > > > Hi Miroslav, > > > > I was tinkering with the "blue-sky" ideas that I mentioned to Josh the other > > day. > > > I dunno if you had a chance to look at what removing that code looks > > like, but I can continue to flesh out that idea if it looks interesting: > > Unfortunately no and I don't think I'll come up with something useful > before LPC, so anything is really welcome. > > > > > https://github.com/joe-lawrence/linux/tree/blue-sky > > > > A full demo would require packaging up replacement .ko's with a livepatch, as > > well as "blacklisting" those deprecated .kos, etc. But that's all I had time > > to cook up last week before our holiday weekend here. > > Frankly, I'm not sure about this approach. I'm kind of torn. The current > solution is far from ideal, but I'm not excited about the other options > either. It seems like the choice is basically between "general but > technically complicated fragile solution with nontrivial maintenance > burden", or "something safer and maybe cleaner, but limiting for > users/distros". Of course it depends on whether the limitation is even > real and how big it is. Unfortunately we cannot quantify it much and that > is probably why our opinions (in the email thread) differ. I wonder what is necessary for a productive discussion on Plumbers: + Josh would like to see what code can get removed when late handling of modules gets removed. I think that it might be partially visible from Joe's blue-sky patches. + I would like to better understand the scope of the current problems. It is about modifying code in the livepatch that depends on position of the related code: + relocations are rather clear; we will need them anyway to access non-public (static) API from the original code. + What are the other changes? + Do we use them in livepatches? How often? + How often new problematic features appear? + Would be possible to detect potential problems, for example by comparing the code in the binary and in memory when the module is loaded the normal way? + Would be possible to reset the livepatch code in memory when the related module is unloaded and safe us half of the troubles? + It might be useful to prepare overview of the existing proposals and agree on the positives and negatives. I am afraid that some of them might depend on the customer base and use cases. Sometimes we might not have enough information. But it might be good to get on the same page where possible. Anyway, it might rule out some variants so that we could better concentrate on the acceptable ones. Or come with yet another proposal that would avoid the real blockers. Any other ideas? Would it be better to discuss this in a separate room with a whiteboard or paperboard? Best Regards, Petr