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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 46F2ACA9EA0 for ; Fri, 18 Oct 2019 13:03:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 177BC222C3 for ; Fri, 18 Oct 2019 13:03:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571403832; bh=lL8Za+mOfGulu5d9ptAB5Ims459ZMBbh69VwNRLPf3I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=viGpf8H6E42lwFd4eUIvzpvRti3J406yNROgmcSKzYUTz8lJOBeYZkRf346H2ZmKc LKbZ8nfMLp7GWBo0cYJNggwc7ZhSEAHqbnWcyT+ytyQz40vvk3A1Oc8db6aJhTv6z4 dzssIWfA5Ku9E4ZipFpLduXQ/AFTyum+Ts3h0Pec= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2442786AbfJRNDu (ORCPT ); Fri, 18 Oct 2019 09:03:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:38870 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732402AbfJRNDu (ORCPT ); Fri, 18 Oct 2019 09:03:50 -0400 Received: from linux-8ccs (charybdis-ext.suse.de [195.135.221.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 629022089C; Fri, 18 Oct 2019 13:03:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571403828; bh=lL8Za+mOfGulu5d9ptAB5Ims459ZMBbh69VwNRLPf3I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=2PiFZp/ttMIY0FneBPAgdpZDNxHFqsWozEphWvtfDcs97tJtvEztr1vZP3g5ZMMuy 5HyfKb5d65lgzxLvRCKTXY9XjZPaYTmEJhMmds0R9KCaiYqOV2Ftg9Sgl3EYieVKdZ T0ca42vumyRuk9azSYRFw5DgGUVRMYvGeXM9cvHg= Date: Fri, 18 Oct 2019 15:03:42 +0200 From: Jessica Yu To: Miroslav Benes Cc: Peter Zijlstra , Steven Rostedt , Joe Lawrence , x86@kernel.org, linux-kernel@vger.kernel.org, mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com, torvalds@linux-foundation.org, tglx@linutronix.de, mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org, ard.biesheuvel@linaro.org, jpoimboe@redhat.com, live-patching@vger.kernel.org, pmladek@suse.com Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke() Message-ID: <20191018130342.GA4625@linux-8ccs> References: <20191015130739.GA23565@linux-8ccs> <20191015135634.GK2328@hirez.programming.kicks-ass.net> <88bab814-ea24-ece9-2bc0-7a1e10a62f12@redhat.com> <20191015153120.GA21580@linux-8ccs> <7e9c7dd1-809e-f130-26a3-3d3328477437@redhat.com> <20191015182705.1aeec284@gandalf.local.home> <20191016074951.GM2328@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-OS: Linux linux-8ccs 4.12.14-lp150.12.28-default x86_64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +++ Miroslav Benes [16/10/19 15:29 +0200]: >On Wed, 16 Oct 2019, Miroslav Benes wrote: > >> On Wed, 16 Oct 2019, Peter Zijlstra wrote: >> >> > On Tue, Oct 15, 2019 at 06:27:05PM -0400, Steven Rostedt wrote: >> > >> > > (7) Seventh session, titled "klp-convert and livepatch relocations", was led >> > > by Joe Lawrence. >> > > >> > > Joe started the session with problem statement: accessing non exported / static >> > > symbols from inside the patch module. One possible workardound is manually via >> > > kallsyms. Second workaround is klp-convert, which actually creates proper >> > > relocations inside the livepatch module from the symbol database during the >> > > final .ko link. >> > > Currently module loader looks for special livepatch relocations and resolves >> > > those during runtime; kernel support for these relocations have so far been >> > > added for x86 only. Special livepatch relocations are supported and processed >> > > also on other architectures. Special quirks/sections are not yet supported. >> > > Plus klp-convert would still be needed even with late module patching update. >> > > vmlinux or modules could have ambiguous static symbols. >> > > >> > > It turns out that the features / bugs below have to be resolved before we >> > > can claim the klp-convert support for relocation complete: >> > > - handle all the corner cases (jump labels, static keys, ...) properly and >> > > have a good regression tests in place >> > >> > I suppose all the patches in this series-of-series here will make life >> > harder for KLP, static_call() and 2 byte jumps etc.. >> >> Yes, I think so. We'll have to deal with that once it lands. That is why >> we want to get rid of all this arch-specific code in livepatch and >> reinvent the late module patching. So it is perhaps better to start >> working on it sooner than later. Adding Petr, who hesitantly signed up for >> the task... > >Thinking about it more... crazy idea. I think we could leverage these new >ELF .text per vmlinux/module sections for the reinvention I was talking >about. If we teach module loader to relocate (and apply alternatives and >so on, everything in arch-specific module_finalize()) not the whole module >in case of live patch modules, but separate ELF .text sections, it could >solve the issue with late module patching we have. It is a variation on >Steven's idea. When live patch module is loaded, only its section for >present modules would be processed. Then whenever a to-be-patched module >is loaded, its .text section in all present patch module would be >processed. > >The upside is that almost no work would be required on patch modules >creation side. The downside is that klp_modinfo must stay. Module loader >needs to be hacked a lot in both cases. So it remains to be seen which >idea is easier to implement. > >Jessica, do you think it would be feasible? I think that does sound feasible. I'm trying to visualize how that would look. I guess there would need to be various livepatching hooks called during the different stages (apply_relocate_add(), module_finalize(), module_enable_ro/x()). So maybe something like the following? When a livepatch module loads: apply_relocate_add() klp hook: apply .klp.rela.$objname relocations *only* for already loaded modules module_finalize() klp hook: apply .klp.arch.$objname changes for already loaded modules module_enable_ro() klp hook: only enable ro/x for .klp.text.$objname for already loaded modules When a to-be-patched module loads: apply_relocate_add() klp hook: for each patch module that patches the coming module, apply .klp.rela.$objname relocations for this object module_finalize() klp hook: for each patch module that patches the coming module, apply .klp.arch.$objname changes for this object module_enable_ro() klp hook: for each patch module, apply ro/x permissions for .klp.text.$objname for this object Then, in klp_module_coming, we only need to do the callbacks and enable the patch, and get rid of the module_disable_ro->apply relocs->module_enable_ro block. Does that sound like what you had in mind or am I totally off? Thanks! Jessica