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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 703EFC10F14 for ; Thu, 3 Oct 2019 09:18:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4D0D82133F for ; Thu, 3 Oct 2019 09:18:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728769AbfJCJSB (ORCPT ); Thu, 3 Oct 2019 05:18:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:54936 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728767AbfJCJSB (ORCPT ); Thu, 3 Oct 2019 05:18:01 -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 E74DBAD73; Thu, 3 Oct 2019 09:17:59 +0000 (UTC) Date: Thu, 3 Oct 2019 11:17:35 +0200 (CEST) From: Miroslav Benes To: Josh Poimboeuf cc: jikos@kernel.org, pmladek@suse.com, joe.lawrence@redhat.com, nstange@suse.de, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 1/3] livepatch: Clear relocation targets on a module removal In-Reply-To: <20191002181817.xpiqiisg5ybtwhru@treble> Message-ID: References: <20190905124514.8944-1-mbenes@suse.cz> <20190905124514.8944-2-mbenes@suse.cz> <20191002181817.xpiqiisg5ybtwhru@treble> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Wed, 2 Oct 2019, Josh Poimboeuf wrote: > On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes wrote: > > Josh reported a bug: > > > > When the object to be patched is a module, and that module is > > rmmod'ed and reloaded, it fails to load with: > > > > module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c > > livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > > livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > > > > The livepatch module has a relocation which references a symbol > > in the _previous_ loading of nfsd. When apply_relocate_add() > > tries to replace the old relocation with a new one, it sees that > > the previous one is nonzero and it errors out. > > > > On ppc64le, we have a similar issue: > > > > module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd] > > livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > > livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > > > > He also proposed three different solutions. We could remove the error > > check in apply_relocate_add() introduced by commit eda9cec4c9a1 > > ("x86/module: Detect and skip invalid relocations"). However the check > > is useful for detecting corrupted modules. > > > > We could also deny the patched modules to be removed. If it proved to be > > a major drawback for users, we could still implement a different > > approach. The solution would also complicate the existing code a lot. > > > > We thus decided to reverse the relocation patching (clear all relocation > > targets on x86_64, or return back nops on powerpc). The solution is not > > universal and is too much arch-specific, but it may prove to be simpler > > in the end. > > > > Reported-by: Josh Poimboeuf > > Signed-off-by: Miroslav Benes > > Since we decided to fix late module patching at LPC, the commit message > and clear_relocate_add() should both probably clarify that these > functions are hacks which are relatively temporary, until we fix the > root cause. It was the plan, but thanks for pointing it out explicitly. I could forget. > But this patch gives me a bad feeling :-/ Not that I have a better > idea. I know what you are talking about. > Has anybody seen this problem in the real world? If not, maybe we'd be > better off just pretending the problem doesn't exist for now. I don't think so. You reported the issue originally and I guess it happened during the testing. Then there is a report from Huawei, but it suggests testing environment too. Reloading modules seems artificial to me. So I agree, we can pretend the issue does not exist and wait for the real solution. Miroslav