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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 0D71FC2D0FA for ; Tue, 12 May 2020 20:46:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D5DDA20747 for ; Tue, 12 May 2020 20:46:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="WVkcmgJK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731279AbgELUqD (ORCPT ); Tue, 12 May 2020 16:46:03 -0400 Received: from linux.microsoft.com ([13.77.154.182]:32968 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731230AbgELUqB (ORCPT ); Tue, 12 May 2020 16:46:01 -0400 Received: from [10.137.106.115] (unknown [131.107.174.243]) by linux.microsoft.com (Postfix) with ESMTPSA id 8F07520B717B; Tue, 12 May 2020 13:46:00 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8F07520B717B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1589316360; bh=5CBxyt/dWjF6Q8OMToqpHYiSWTCEtvdB+pOe8gCrEfY=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=WVkcmgJKlWO5sd4Ym7b0twaJ+ocp8Snnig3oIZ4pkHn5pnUqY1BXmXCY3Bw+51Z+s X90hUe60ZiR2AqWXSpEUbn/uS2FeXHExR8GoMGidsjLfC2sHzVzjim1o7dW4T+oGkA YCQzgAz1MQbdE6JNrLOTlL8TZo6s1APo8nKYqtFc= Subject: Re: [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) From: Deven Bowers To: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= , 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> Message-ID: <8ba7b15f-de91-40f7-fc95-115228345fce@linux.microsoft.com> Date: Tue, 12 May 2020 13:46:00 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <0001755a-6b2a-b13b-960c-eb0b065c8e3c@linux.microsoft.com> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: 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 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?