Received: by 2002:a05:6358:7058:b0:131:369:b2a3 with SMTP id 24csp267084rwp; Wed, 12 Jul 2023 13:01:14 -0700 (PDT) X-Google-Smtp-Source: APBJJlGHiFCRAh5tw8eiP7UUSbuxfXaOu4LYbcj8c4haz5VQZfSJeFywYv7MsgQvZOu3Nz2cDKi0 X-Received: by 2002:a2e:700e:0:b0:2b5:97a3:3ba5 with SMTP id l14-20020a2e700e000000b002b597a33ba5mr16931810ljc.10.1689192074293; Wed, 12 Jul 2023 13:01:14 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1689192074; cv=none; d=google.com; s=arc-20160816; b=l+vQws4sbAU6yjj6yKNCV6Yceo+raKWeuHzEcHMczNlJCjEyfguEBRe4LMFAY/wuv1 89BYQ7Apjf6+YmicyqR8xDwdjDIlpUyLSyp1+iI8HlM1O4KQTpSQ99fgQGjPHTt7H5gU yODvX4lXtxBX0OykUD0F1Oomc1lQ/Ot+vTsuD0ekqR6kGfLQvSPhX2/wBsGs2KNEGcJz 9Ox52czzr+jq6+H2b6a+KXkQ+kTIEBknDwg9zAvfr0A96DHQQYz7S/KLMvv015OG5YJU QrGwECODyeRPAYNzJl6cbsOGGy/paPjpbModGjHTJUP/Mdaw4XAcC29XSqyixphUDRbU Imkw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:dkim-signature; bh=nNWmY600V/PLRHoZZiov2iopw51kXSqX0Yxuxxsh3Nc=; fh=saGguLTWLQEvWI+Icc3BWJzHdo6ZtTQgRr/suedWUsI=; b=jQS2HrfINMH2bPHElDth5/MRXZjchgtyix+RLRCH1RQF4ggJrePlqjr3vx4W3DP2XG +kKzvOpqdbeHz2WuqHi5m41k/s4XK12zLQrrT93WxphfpQT40QP+xykLFXxAe1UBsNru DdI9J2tSEv5EZTmXHRJeOjSLkZFV2SoNxogLVYCZmTvLN7dbaysK8uLOd8xdBvBpiILg LtCV+xbtwRCONLWm/XJrjXrJaIZIfuVH3htN+WFg+F55sm9VDs/Eg7lGl92/Wv2E2NsE IidmrSIBNG/BhWuxP7IFv+Lg4IXsR3rPzjiossyeorURyuhtp8q/1Sgl6kNwZcfz/ekk 8lkg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b="U/qhzHOJ"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Return-Path: Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id i3-20020a1709063c4300b00988e963c3adsi5260659ejg.755.2023.07.12.13.00.49; Wed, 12 Jul 2023 13:01:14 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b="U/qhzHOJ"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232184AbjGLTFr (ORCPT + 99 others); Wed, 12 Jul 2023 15:05:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232203AbjGLTFq (ORCPT ); Wed, 12 Jul 2023 15:05:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72221198A for ; Wed, 12 Jul 2023 12:05:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B6CAD618E1 for ; Wed, 12 Jul 2023 19:05:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97D99C433C8; Wed, 12 Jul 2023 19:05:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1689188743; bh=3DbaRTzEFa6CkTmOVe6DWh7txs54oIASotaLhI9p7xs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=U/qhzHOJdeEl9IHpJf18gix0KpKzIC78LoV+GTlV4RLWWL6MQk5nyxaXfhURBeIhg tfG1gJyKuYVbJ/rWX1Qf4ql9gqbqkhSzgn54azZcMoOEUrwLgEC/RiD9z9Zq+uCHoq OywqMU/TTg0oyvFUeYdMerEAbP6Ox7ebwGG0ZHI8= Date: Wed, 12 Jul 2023 21:05:40 +0200 From: Greg KH To: Luca Boccassi Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Borislav Petkov , Emanuele Giuseppe Esposito , "H. Peter Anvin" , x86@kernel.org, Thomas Gleixner , lennart@poettering.net, Ingo Molnar , Dave Hansen , Andrew Morton , Masahiro Yamada , Alexander Potapenko , Nick Desaulniers , Vitaly Kuznetsov , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2] x86/boot: add .sbat section to the bzImage Message-ID: <2023071229-dusk-repacking-da3a@gregkh> References: <7E9D397B-439F-484C-B950-9094605A7B4D@zytor.com> <5e01b6a5-f993-f99d-41a0-ab671ec598f8@redhat.com> <20230712120002.GIZK6Vwga6DlJqdjEh@fat_crate.local> <20230712132840.GKZK6qiK70m1O90jFL@fat_crate.local> <2023071200-unopposed-unbuckled-cde8@gregkh> <2023071239-progress-molasses-3b3d@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 12, 2023 at 07:59:12PM +0100, Luca Boccassi wrote: > On Wed, 12 Jul 2023 at 17:57, Greg KH wrote: > > > > On Wed, Jul 12, 2023 at 05:23:18PM +0100, Luca Boccassi wrote: > > > On Wed, 12 Jul 2023 at 16:43, Greg KH wrote: > > > > > > > > On Wed, Jul 12, 2023 at 03:06:46PM +0100, Daniel P. Berrang? wrote: > > > > > On Wed, Jul 12, 2023 at 03:28:40PM +0200, Borislav Petkov wrote: > > > > > > On Wed, Jul 12, 2023 at 01:48:45PM +0100, Daniel P. Berrang? wrote: > > > > > > > That doesn't make it useless, as the 3rd/4th/5th fields in the SBAT > > > > > > > file are just human targetted metadata. The validation process just > > > > > > > works off the 1st/2nd field. > > > > > > > > > > > > It's a good thing I asked - feels like I'm just scratching the surface > > > > > > on what this thing actually is and the commit message is not explaining > > > > > > any of that. > > > > > > > > > > > > First, second field, that's what, "linux,1"? > > > > > > > > > > Each sbat CSV file line has following fields: > > > > > > > > > > component_name: the name we're comparing > > > > > component_generation: the generation number for the comparison > > > > > vendor_name: human readable vendor name > > > > > vendor_package_name: human readable package name > > > > > vendor_version: human readable package version (maybe machine parseable too, not specified here) > > > > > vendor_url: url to look stuff up, contact, whatever. > > > > > > > > > > So 'linux' is 'component_name' and '1' is component_generation > > > > > > > > > > > > From a functional POV, it doesn't have to be unique identified, > > > > > > > as it is just a human targetted metadata field. A friendly git > > > > > > > version as from 'git describe' is more appropriate than a build > > > > > > > ID sha. > > > > > > > > > > > > So can you explain what exactly that version is supposed to describe? > > > > > > Exact kernel sources the kernel was built from? Or a random, increasing > > > > > > number which tools can use to mark as bad? > > > > > > > > > > AFAICT beyond being "human readable package version", it is a fairly > > > > > arbitrary decision. A release version number for formal releases, or > > > > > a 'git describe' version string for git snapshots both satisfy the > > > > > versioning requirement IMHO. > > > > > > > > > > > How do you prevent people from binary-editing that section? Secure boot > > > > > > does that because that changes the signed kernel image? > > > > > > > > > > The PE files are signed by the vendor who builds them, using their > > > > > SecureBoot signing key. The data covered by the signature includes > > > > > the '.sbat' section. > > > > > > > > > > IOW, if you binary edit the section, the SecureBoot signature > > > > > verification fails and the kernel won't be booted. > > > > > > > > > > > > > And then why does it have to be a separate section? All those > > > > > > > > requirements need to be written down. > > > > > > > > > > > > You missed this question. > > > > > > > > > > That's simply what the spec defines as the approach. > > > > > > > > > > The PE file format used by EFI applications has multiple > > > > > sections and the spec has declare that the '.sbat' section > > > > > is where this data shall live. > > > > > > > > > > > > The first line just identifies the file format and should > > > > > > > never change: > > > > > > > > > > > > > > sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md > > > > > > > > > > > > Why do you even need it then? > > > > > > > > > > First it identifies the data format, and second if a > > > > > problem is ever discovered with the SBAT concept, > > > > > a fixed approach can be indicated by changing to > > > > > 'sbat,2,.....' and thus have the effect of revoking > > > > > use of any binaries which declare the 'sbat,1,....' > > > > > version. Pretty unlikely this will happen, but a useful > > > > > backup plan/safety net. > > > > > > > > > > > > The second line identifies the kernel generation > > > > > > > > > > > > > > linux,1,The Linux Developers,linux,6.5.0-rc1,https://linux.org > > > > > > > > > > > > > > The first field 'linux' should never change once decided upon, as it is > > > > > > > the name of the upstream project's EFI component - in this case the > > > > > > > linux kernel. > > > > > > > > > > > > > > The second field '1' is the most important one, as it is the mechanism > > > > > > > through which revokation takes places, and the only one a human upstream > > > > > > > maintainer should manually change. > > > > > > > > > > > > Hold on, how often are those things going to change? And who's going to > > > > > > change them? I sure hope we won't start getting patches constantly > > > > > > updating those numbers? > > > > > > > > > > It is hard to predict the future, but my gut feeling is very infrequently. > > > > > > > > Have you looked at the past as proof of this? > > > > > > I can't quite think of relevant bugs, in the recent past. Are you > > > aware of past instances of kernel module signature verification being > > > broken? Or userspace being allowed to do arbitrary kernel memory > > > manipulation before ExitBootServices? > > > > Yes. > > Then you already know the answer w.r.t. frequency I have a clue, yes. But given that others do not that are proposing this, that's quite worrying. > > And no, I will not provide examples for obvious reasons. > > Security-through-obscurity? Nice! That's not what this is, please see the many places this is explained in detail. If you wish to discuss how the kernel security team handles known security fixes, we can do so on a relevant thread (i.e. not this one.) > > > > > I can't say I recall any specific Linux bugs that would warrant it, but > > > > > those involved in Linux/Bootloade/SecureBoot world can probably answer > > > > > this better than me. IIUC, the scope of bugs relevent to this is quite > > > > > narrow. > > > > > > > > Really? I know a lot of people who would disagree... > > > > > > They'd better have some convincing reasons > > > > > > > > > > If there is discovered a flaw in Linux that allows the Secure Boot chain > > > > > > > to be broken (eg some flaw allowed linux to be exploited as a mechanism > > > > > > > to load an unsigned binary), then this 'generation' number would need > > > > > > > to be incremented when a fix is provided in upstream Linux trees. > > > > > > > > > > > > Oh boy, there it is. And then when those fixes need to be backported to > > > > > > stable, then those patches updating that number would need to be > > > > > > backported too. I can already see the mess on the horizon. > > > > > > > > > > If applicable, yes. > > > > > > > > And how are you going to determine this? > > > > > > Same as it's done for the bootloaders - does it enable a secure boot > > > bypass -> yes/no > > > > And how are you going to determine this? Seriously, please explain the > > auditing you are going to do here and who is going to maintain it and > > fund the effort? > > Same way it is determined for Shim, Grub, sd-boot, Windows BootMngr, > etc - maintainers doing their jobs, researchers poking at them, or if > we are particularly unlucky by live exploits in the wild. I'm not > exactly sure where the confusion comes from, none of this is novel. But why does any of this matter at all? Just use the kernel version (which is already in the image), and be done with it. We always increment it so all should be fine. If a distro wants to track how they add various fixes/changes/hacks/etc to the kernel image, that's fine for them to do so too, but it doesn't deserve some opaque "epoch number" like you all are proposing here. thanks, greg k-h