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=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 C0B08C10F14 for ; Wed, 2 Oct 2019 18:18:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A983A218DE for ; Wed, 2 Oct 2019 18:18:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728543AbfJBSSX (ORCPT ); Wed, 2 Oct 2019 14:18:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50130 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726669AbfJBSSX (ORCPT ); Wed, 2 Oct 2019 14:18:23 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BBDAD18CB8F3; Wed, 2 Oct 2019 18:18:22 +0000 (UTC) Received: from treble (ovpn-121-106.rdu2.redhat.com [10.10.121.106]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5A00160A97; Wed, 2 Oct 2019 18:18:19 +0000 (UTC) Date: Wed, 2 Oct 2019 13:18:17 -0500 From: Josh Poimboeuf To: Miroslav Benes 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 Message-ID: <20191002181817.xpiqiisg5ybtwhru@treble> References: <20190905124514.8944-1-mbenes@suse.cz> <20190905124514.8944-2-mbenes@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190905124514.8944-2-mbenes@suse.cz> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.63]); Wed, 02 Oct 2019 18:18:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. But this patch gives me a bad feeling :-/ Not that I have a better idea. 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. -- Josh