From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752646AbcGFCfd (ORCPT ); Tue, 5 Jul 2016 22:35:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51185 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751252AbcGFCfa (ORCPT ); Tue, 5 Jul 2016 22:35:30 -0400 From: Jessica Yu To: Josh Poimboeuf , Miroslav Benes , Petr Mladek , Jiri Kosina , Chris J Arges , Eugene Shatokhin Cc: live-patching@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Jessica Yu Subject: [PATCH 0/2] Fix issue with alternatives/paravirt patches Date: Tue, 5 Jul 2016 22:34:58 -0400 Message-Id: <1467772500-26092-1-git-send-email-jeyu@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 06 Jul 2016 02:35:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, A few months ago, Chris Arges reported a bug involving alternatives/paravirt patching that was discussed here [1] and here [2]. To briefly summarize the bug, patch modules that contained .altinstructions or .parainstructions sections would break because these alternative/paravirt patches would be applied first by the module loader (see x86 module_finalize()), then livepatch would later clobber these patches when applying per-object relocations. This lead to crashes and unpredictable behavior. One conclusion we reached from our last discussion was that we will need to introduce some arch-specific code to address this problem. This patchset presents a possible fix for the bug by adding a new arch-specific arch_klp_init_object_loaded() function that by default does nothing but can be overridden by different arches. To fix this issue for x86, since we can access a patch module's Elf sections through mod->klp_info, we can simply delay the calls to apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(), which is called after relocations have been written for an object. In addition, for patch modules, .parainstructions and .altinstructions are prefixed by ".klp.arch.${objname}" so that the module loader ignores them and livepatch can apply them manually. Currently for kpatch, we don't support including jump table sections in the patch module, and supporting .smp_locks is currently broken, so we don't consider those sections (for now). I did some light testing with some patches to kvm and verified that the original issue reported in [2] was fixed. Based on linux-next. [1] http://thread.gmane.org/gmane.linux.kernel/2185604/ [2] https://github.com/dynup/kpatch/issues/580 Jessica Yu (2): livepatch: use arch_klp_init_object_loaded() to finish arch-specific tasks livepatch/x86: apply alternatives and paravirt patches after relocations arch/x86/kernel/Makefile | 1 + arch/x86/kernel/livepatch.c | 66 +++++++++++++++++++++++++++++++++++++++++++++ include/linux/livepatch.h | 3 +++ kernel/livepatch/core.c | 12 +++++++-- 4 files changed, 80 insertions(+), 2 deletions(-) create mode 100644 arch/x86/kernel/livepatch.c -- 2.4.3