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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 41CC1C48BDF for ; Wed, 16 Jun 2021 02:39:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2AF2461369 for ; Wed, 16 Jun 2021 02:39:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231959AbhFPClk (ORCPT ); Tue, 15 Jun 2021 22:41:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231997AbhFPCli (ORCPT ); Tue, 15 Jun 2021 22:41:38 -0400 Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF6D5C061574 for ; Tue, 15 Jun 2021 19:39:32 -0700 (PDT) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4G4Tst5V3Xz9sTD; Wed, 16 Jun 2021 12:39:30 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1623811170; bh=imTZXZdnzJHPt2ZWyWGHRNA6wmOp1nSPOi8QzrlkB4s=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=HFV/sTAX53bf9R+6Dm3zy428RVTv2CttzChX6iY6NYOIzRmlgXF3OFoBjB7BPE8BG /bChHWVQOR7cC6khg4yoGgO9VJEYXjaY3vS/juv5fngCzofmfZmCTXmr6xxRbLRS5i BBqUlr6sHCaShQ9THEmts03bqT12lnuLlbc3Apc3yKA17MVqMDfQ6I8meOnV7WLNoQ KbhipHpWWsqqO51dm4r7NuHN5d2KWpjUa1xAzSryYSFUH2NHTUuvf0rv3+QRsX2QXy YGTFkMFMukem+2xGONbdMGSgSFo54KmV0IAN6Jn5gQJOf1pV/cwqEEZV7AEdNmxr5Y +Wfp2MshMxLRw== From: Michael Ellerman To: Segher Boessenkool , Jessica Yu Cc: Nicholas Piggin , Michal =?utf-8?Q?Such=C3=A1nek?= , 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 In-Reply-To: <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> <20210615143038.GH5077@gate.crashing.org> Date: Wed, 16 Jun 2021 12:39:30 +1000 Message-ID: <87sg1isfbx.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Segher Boessenkool writes: > 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 :-/ Yeah elf_check_arch() is already called from elf_validity_check(), and that call would remain. cheers