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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 188B5C3A5A5 for ; Thu, 5 Sep 2019 13:15:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4A5A2067D for ; Thu, 5 Sep 2019 13:15:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388379AbfIENPL (ORCPT ); Thu, 5 Sep 2019 09:15:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34742 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731758AbfIENPL (ORCPT ); Thu, 5 Sep 2019 09:15:11 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4B8B130860D1; Thu, 5 Sep 2019 13:15:11 +0000 (UTC) Received: from treble (ovpn-120-170.rdu2.redhat.com [10.10.120.170]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CDB4C5D6A3; Thu, 5 Sep 2019 13:15:04 +0000 (UTC) Date: Thu, 5 Sep 2019 08:15:02 -0500 From: Josh Poimboeuf To: Petr Mladek Cc: jikos@kernel.org, Joe Lawrence , Miroslav Benes , 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: <20190905131502.mgiaplb3grlxsahp@treble> References: <20190822223649.ptg6e7qyvosrljqx@treble> <20190823081306.kbkm7b4deqrare2v@pathway.suse.cz> <20190826145449.wyo7avwpqyriem46@treble> <5c649320-a9bf-ae7f-5102-483bc34d219f@redhat.com> <20190904084932.gndrtewubqiaxmzy@pathway.suse.cz> <20190905025055.36loaatxtkhdo4q5@treble> <20190905110955.wl4lwjbnpqybhkcn@pathway.suse.cz> <20190905130832.dznviqrrg6lfrxvx@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190905130832.dznviqrrg6lfrxvx@treble> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 05 Sep 2019 13:15:11 +0000 (UTC) Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, Sep 05, 2019 at 08:08:32AM -0500, Josh Poimboeuf wrote: > On Thu, Sep 05, 2019 at 01:09:55PM +0200, Petr Mladek wrote: > > > I don't have a number, but it's very common to patch a function which > > > uses jump labels or alternatives. > > > > Really? My impression is that both alternatives and jump_labels > > are used in hot paths. I would expect them mostly in core code > > that is always loaded. > > > > Alternatives are often used in assembly that we are not able > > to livepatch anyway. > > > > Or are they spread widely via some macros or inlined functions? > > Jump labels are used everywhere. Looking at vmlinux.o in my kernel: > > Relocation section [19621] '.rela__jump_table' for section [19620] '__jump_table' at offset 0x197873c8 contains 11913 entries: > > Each jump label entry has 3 entries, so 11913/3 = 3971 jump labels. > > $ readelf -s vmlinux.o |grep FUNC |wc -l > 46902 > > 3971/46902 = ~8.5% > > ~8.5% of functions use jump labels. Obviously some functions may use more than one jump label so this isn't exactly bulletproof math. But it gives a rough idea of how widespread they are. > > > > > + How often new problematic features appear? > > > > > > I'm not exactly sure what you mean, but it seems that anytime we add a > > > new feature, we have to try to wrap our heads around how it interacts > > > with the weirdness of late module patching. > > > > I agree that we need to think about it and it makes complications. > > Anyway, I think that these are never the biggest problems. > > > > I would be more concerned about arch-specific features that might need > > special handling in the livepatch code. Everyone talks only about > > alternatives and jump_labels that were added long time ago. > > Jump labels have been around for many years, but we somehow missed > implementing klp.arch for them. As I said this resulted in panics. > > There may be other similar cases lurking, both in x86 and other arches. > It's not a comforting thought! > > And each case requires special klp code in addition to the real code. > > -- > Josh -- Josh