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=BAYES_00, 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 91DFFC48BE5 for ; Tue, 15 Jun 2021 14:33:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DDCE61490 for ; Tue, 15 Jun 2021 14:33:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231350AbhFOOfw (ORCPT ); Tue, 15 Jun 2021 10:35:52 -0400 Received: from gate.crashing.org ([63.228.1.57]:54008 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231307AbhFOOfv (ORCPT ); Tue, 15 Jun 2021 10:35:51 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 15FEUdaR001580; Tue, 15 Jun 2021 09:30:39 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 15FEUc51001579; Tue, 15 Jun 2021 09:30:38 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 15 Jun 2021 09:30:38 -0500 From: Segher Boessenkool To: Jessica Yu Cc: Nicholas Piggin , Michal =?iso-8859-1?Q?Such=E1nek?= , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks Message-ID: <20210615143038.GH5077@gate.crashing.org> References: <20210611093959.821525-1-npiggin@gmail.com> <20210611093959.821525-2-npiggin@gmail.com> <1623722110.amu32mwaqs.astroid@bobo.none> <20210615125057.GF5077@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 15, 2021 at 03:41:00PM +0200, Jessica Yu wrote: > +++ Segher Boessenkool [15/06/21 07:50 -0500]: > >On Tue, Jun 15, 2021 at 02:17:40PM +0200, Jessica Yu wrote: > >>+int __weak elf_check_module_arch(Elf_Ehdr *hdr) > >>+{ > >>+ return 1; > >>+} > > > >But is this a good idea? It isn't useful to be able to attempt to load > >a module not compiled for your architecture, and it increases the attack > >surface tremendously. These checks are one of the few things that can > >*not* be weak symbols, imo. > > Hm, could you please elaborate a bit more? This patchset is adding > extra Elf header checks specifically for powerpc, and the module > loader usually provides arch-specific hooks via weak symbols. We are > just providing an new hook here, which should act as a no-op if it > isn't used. > > So if an architecture wants to provide extra header checks, it can do > so by overriding the new weak symbol. Otherwise, the weak function acts as > a noop. We also already have the existing elf_check_arch() check for each > arch and that is *not* a weak symbol. The way I read your patch the default elf_check_module_arch does not call elf_check_arch? Is that clearly called elsewhere and I'm just dumb again? Sorry for the distraction in that case :-/ Segher