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[68.160.176.52]) by smtp.gmail.com with ESMTPSA id w140-20020a376292000000b006a10aa7908dsm108133qkb.38.2022.05.18.13.03.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 May 2022 13:03:45 -0700 (PDT) Date: Wed, 18 May 2022 16:03:44 -0400 From: Mike Snitzer To: Matthias Kaehlcke Message-ID: References: <20220517233457.1123309-1-mka@chromium.org> <20220517163437.v4.1.I3e928575a23481121e73286874c4c2bdb403355d@changeid> <19149028-ec94-8f64-aed4-1e58f29942a8@gmail.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Subject: Re: [dm-devel] [PATCH v4 1/3] dm: Add verity helpers for LoadPin X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-security-module@vger.kernel.org, Kees Cook , linux-kernel@vger.kernel.org, James Morris , Douglas Anderson , linux-raid@vger.kernel.org, Song Liu , dm-devel@redhat.com, Milan Broz , Alasdair Kergon , "Serge E . Hallyn" Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, May 18 2022 at 11:13P -0400, Matthias Kaehlcke wrote: > Hi Milan, > > On Wed, May 18, 2022 at 09:57:43AM +0200, Milan Broz wrote: > > On 18/05/2022 01:34, Matthias Kaehlcke wrote: > > > LoadPin limits loading of kernel modules, firmware and certain > > > other files to a 'pinned' file system (typically a read-only > > > rootfs). To provide more flexibility LoadPin is being extended > > > to also allow loading these files from trusted dm-verity > > > devices. For that purpose LoadPin can be provided with a list > > > of verity root digests that it should consider as trusted. > > > > > > Add a bunch of helpers to allow LoadPin to check whether a DM > > > device is a trusted verity device. The new functions broadly > > > fall in two categories: those that need access to verity > > > internals (like the root digest), and the 'glue' between > > > LoadPin and verity. The new file dm-verity-loadpin.c contains > > > the glue functions. > > > > > > Signed-off-by: Matthias Kaehlcke > > > > ... > > > > > + > > > + if (dm_verity_get_root_digest(ti, &root_digest, &digest_size)) > > > + return false; > > > > Almost unrelated note, but as there are more and more situations > > that checks verity root digest, shouldn't we export this as read-only > > sysfs attribute for DM verity devices? > > > > Attacker can always calculate (but not change) Merkle tree, so this > > is not something that need to be hidden. > > > > It would allow userspace to easily enumerate trusted DM devices without > > calling kernel ioctls... > > I guess that's an option if there are scenarios where it is useful. It > should probably be a separate patch, since it isn't directly related with > extending LoadPin support to trusted verity devices. > > > > + > > > + table = dm_get_live_table(md, &srcu_idx); > > > + > > > + if (dm_table_get_num_targets(table) != 1) > > > + goto out; > > > + > > > + ti = dm_table_get_target(table, 0); > > > + > > > + if (is_trusted_verity_target(ti)) > > > + trusted = true; > > > > What happens is someone reloads verity table later with > > a different content (or even different target type)? > > Does LoadPin even care here? > > LoadPin cares, but only when new kernel files are loaded. It will then check > against the new verity table, and only allow loading of the file if it comes > from a verity target with a trusted digest. > > > > static struct target_type verity_target = { > > > .name = "verity", > > > .version = {1, 8, 0}, > > > > Please increase the minor version, it is very useful to detect (in logs) > > that the target driver has compatible extensions. > > I can do that, but would like to confirm that this is really needed/desired. > This patch adds kernel-internal APIs which aren't accessible to userspace, > that don't impact verity directly, so I'm not sure an increased minor version > would be useful. Bumping to 1.8.1 is useful to indicate new changes that offer expanded use of the verity target (even if by LoadPin). -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel 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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D90FFC433EF for ; Wed, 18 May 2022 20:03:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242209AbiERUDt (ORCPT ); Wed, 18 May 2022 16:03:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242110AbiERUDs (ORCPT ); Wed, 18 May 2022 16:03:48 -0400 Received: from mail-qk1-f174.google.com (mail-qk1-f174.google.com [209.85.222.174]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5FA7C2370F8 for ; Wed, 18 May 2022 13:03:46 -0700 (PDT) Received: by mail-qk1-f174.google.com with SMTP id a22so2357998qkl.5 for ; Wed, 18 May 2022 13:03:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7Qpd/J7A8SCSKU6yZw0hxy+iztL0Wu+jzDVTa+YGvyo=; b=QuSybfOTcI5PhXb0dq+09mxRifQsN9HGRwYB/Sj4AEbmf7SRd1W50g0SNmqmsZs2v7 0V/jytS3v827Qd0pz4RxQ/4shb4puizPOFamxW9Ds6LMZVrXGiEgtFxoDZeR7lQZw6Y1 xylMB/8QkqNC5ErG+kxsE7c1J1BqCeIBYjXGlfPQy+JZLfXDNsbjqeA0vjfcrgnyKprk 1BCLoYp42S7jIeCOokAP/yT15ZaOedVXOYxJWsUS/cWgxl7Yhq3+xuAWKJ3VAs7QWnS/ +UNsOakYat1xB878yusOPyUKEai+1HP71D6U1u7/yzTpTcTiGfublWfxSyPRjls1MHhw uZnQ== X-Gm-Message-State: AOAM530d+9RmUj8Z8XWYWhFXZV73MjIlh1iY/1aPfwaiFMlZrnX9Ha9I 5g9aYRynOaD2x906J1J+3X0J X-Google-Smtp-Source: ABdhPJwEU5F9uKrOZEN4PLvxlHlsC7JKL94tfNkKx/c8tpQgbDVfOXmn74Adm6rOuDC33973uwbA2A== X-Received: by 2002:a05:620a:4612:b0:6a0:125b:56be with SMTP id br18-20020a05620a461200b006a0125b56bemr821947qkb.369.1652904225547; Wed, 18 May 2022 13:03:45 -0700 (PDT) Received: from localhost (pool-68-160-176-52.bstnma.fios.verizon.net. [68.160.176.52]) by smtp.gmail.com with ESMTPSA id w140-20020a376292000000b006a10aa7908dsm108133qkb.38.2022.05.18.13.03.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 May 2022 13:03:45 -0700 (PDT) Date: Wed, 18 May 2022 16:03:44 -0400 From: Mike Snitzer To: Matthias Kaehlcke Cc: Milan Broz , Alasdair Kergon , Kees Cook , James Morris , "Serge E . Hallyn" , dm-devel@redhat.com, Douglas Anderson , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Song Liu , linux-security-module@vger.kernel.org Subject: Re: [PATCH v4 1/3] dm: Add verity helpers for LoadPin Message-ID: References: <20220517233457.1123309-1-mka@chromium.org> <20220517163437.v4.1.I3e928575a23481121e73286874c4c2bdb403355d@changeid> <19149028-ec94-8f64-aed4-1e58f29942a8@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Wed, May 18 2022 at 11:13P -0400, Matthias Kaehlcke wrote: > Hi Milan, > > On Wed, May 18, 2022 at 09:57:43AM +0200, Milan Broz wrote: > > On 18/05/2022 01:34, Matthias Kaehlcke wrote: > > > LoadPin limits loading of kernel modules, firmware and certain > > > other files to a 'pinned' file system (typically a read-only > > > rootfs). To provide more flexibility LoadPin is being extended > > > to also allow loading these files from trusted dm-verity > > > devices. For that purpose LoadPin can be provided with a list > > > of verity root digests that it should consider as trusted. > > > > > > Add a bunch of helpers to allow LoadPin to check whether a DM > > > device is a trusted verity device. The new functions broadly > > > fall in two categories: those that need access to verity > > > internals (like the root digest), and the 'glue' between > > > LoadPin and verity. The new file dm-verity-loadpin.c contains > > > the glue functions. > > > > > > Signed-off-by: Matthias Kaehlcke > > > > ... > > > > > + > > > + if (dm_verity_get_root_digest(ti, &root_digest, &digest_size)) > > > + return false; > > > > Almost unrelated note, but as there are more and more situations > > that checks verity root digest, shouldn't we export this as read-only > > sysfs attribute for DM verity devices? > > > > Attacker can always calculate (but not change) Merkle tree, so this > > is not something that need to be hidden. > > > > It would allow userspace to easily enumerate trusted DM devices without > > calling kernel ioctls... > > I guess that's an option if there are scenarios where it is useful. It > should probably be a separate patch, since it isn't directly related with > extending LoadPin support to trusted verity devices. > > > > + > > > + table = dm_get_live_table(md, &srcu_idx); > > > + > > > + if (dm_table_get_num_targets(table) != 1) > > > + goto out; > > > + > > > + ti = dm_table_get_target(table, 0); > > > + > > > + if (is_trusted_verity_target(ti)) > > > + trusted = true; > > > > What happens is someone reloads verity table later with > > a different content (or even different target type)? > > Does LoadPin even care here? > > LoadPin cares, but only when new kernel files are loaded. It will then check > against the new verity table, and only allow loading of the file if it comes > from a verity target with a trusted digest. > > > > static struct target_type verity_target = { > > > .name = "verity", > > > .version = {1, 8, 0}, > > > > Please increase the minor version, it is very useful to detect (in logs) > > that the target driver has compatible extensions. > > I can do that, but would like to confirm that this is really needed/desired. > This patch adds kernel-internal APIs which aren't accessible to userspace, > that don't impact verity directly, so I'm not sure an increased minor version > would be useful. Bumping to 1.8.1 is useful to indicate new changes that offer expanded use of the verity target (even if by LoadPin).