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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 83D09C433E0 for ; Thu, 14 May 2020 19:28:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64AFA20643 for ; Thu, 14 May 2020 19:28:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728240AbgENT2T (ORCPT ); Thu, 14 May 2020 15:28:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726132AbgENT2T (ORCPT ); Thu, 14 May 2020 15:28:19 -0400 Received: from smtp-8fad.mail.infomaniak.ch (smtp-8fad.mail.infomaniak.ch [IPv6:2001:1600:3:17::8fad]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 09427C061A0C for ; Thu, 14 May 2020 12:28:19 -0700 (PDT) Received: from smtp-3-0000.mail.infomaniak.ch (unknown [10.4.36.107]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 49NM5Y60DmzlhGVS; Thu, 14 May 2020 21:28:17 +0200 (CEST) Received: from ns3096276.ip-94-23-54.eu (unknown [94.23.54.103]) by smtp-3-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 49NM5X23j6zljVWn; Thu, 14 May 2020 21:28:16 +0200 (CEST) Subject: Re: [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) To: Deven Bowers , agk@redhat.com, axboe@kernel.dk, snitzer@redhat.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, dm-devel@redhat.com, linux-block@vger.kernel.org, jannh@google.com Cc: tyhicks@linux.microsoft.com, pasha.tatashin@soleen.com, sashal@kernel.org, jaskarankhurana@linux.microsoft.com, nramas@linux.microsoft.com, mdsakib@linux.microsoft.com, linux-kernel@vger.kernel.org, corbet@lwn.net References: <20200415162550.2324-1-deven.desai@linux.microsoft.com> <0001755a-6b2a-b13b-960c-eb0b065c8e3c@linux.microsoft.com> <8ba7b15f-de91-40f7-fc95-115228345fce@linux.microsoft.com> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Message-ID: <44fb36ae-959d-4ff7-ed1f-ccfc2e292232@digikod.net> Date: Thu, 14 May 2020 21:28:15 +0200 User-Agent: MIME-Version: 1.0 In-Reply-To: <8ba7b15f-de91-40f7-fc95-115228345fce@linux.microsoft.com> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/05/2020 22:46, Deven Bowers wrote: > > > On 5/11/2020 11:03 AM, Deven Bowers wrote: >> >> >> On 5/10/2020 2:28 AM, Mickaël Salaün wrote: >> >> [...snip] >> >>>> >>>> Additionally, rules are evaluated top-to-bottom. As a result, any >>>> revocation rules, or denies should be placed early in the file to >>>> ensure >>>> that these rules are evaluated before a rule with "action=ALLOW" is >>>> hit. >>>> >>>> IPE policy is designed to be forward compatible and backwards >>>> compatible, >>>> thus any failure to parse a rule will result in the line being ignored, >>>> and a warning being emitted. If backwards compatibility is not >>>> required, >>>> the kernel commandline parameter and sysctl, ipe.strict_parse can be >>>> enabled, which will cause these warnings to be fatal. >>> >>> Ignoring unknown command may lead to inconsistent beaviors. To achieve >>> forward compatibility, I think it would be better to never ignore >>> unknown rule but to give a way to userspace to known what is the current >>> kernel ABI. This could be done with a securityfs file listing the >>> current policy grammar. >>> >> >> That's a fair point. From a manual perspective, I think this is fine. >> A human-user can interpret a grammar successfully on their own when new >> syntax is introduced. >> >>  From a producing API perspective, I'd have to think about it a bit >> more. Ideally, the grammar would be structured in such a way that the >> userland >> interpreter of this grammar would not have to be updated once new syntax >> is introduced, avoiding the need to update the userland binary. To do so >> generically ("op=%s") is easy, but doesn't necessarily convey sufficient >> information (what happens when a new "op" token is introduced?). I think >> this may come down to regular expression representations of valid values >> for these tokens, which worries me as regular expressions are incredibly >> error-prone[1]. >> >> I'll see what I can come up with regarding this. > > I have not found a way that I like to expose some kind of grammar > through securityfs that can be understood by usermode to parse the > policy. Here's what I propose as a compromise: > >     1. I remove the unknown command behavior. This address your > first point about inconsistent behaviors, and effectively removes the > strict_parse sysctl (as it is always enabled). > >     2. I introduce a versioning system for the properties > themselves. The valid set of properties and their versions > can be found in securityfs, under say, ipe/config in a key=value > format where `key` indicates the understood token, and `value` > indicates their current version. For example: > >     $ cat $SECURITYFS/ipe/config >     op=1 >     action=1 >     policy_name=1 >     policy_version=1 >     dmverity_signature=1 >     dmverity_roothash=1 >     boot_verified=1 The name ipe/config sounds like a file to configure IPE. Maybe something like ipe/config_abi or ipe/config_grammar? > > if new syntax is introduced, the version number is increased. > >     3. The format of those versions are documented as part of > the admin-guide around IPE. If user-mode at that point wants to rip > the documentation formats and correlate with the versioning, then > it fulfills the same functionality as above, with out the complexity > around exposing a parsing grammar and interpreting it on-the-fly. > Many of these are unlikely to move past version 1, however. > > Thoughts? > That seems reasonable.