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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 1964CC33C9E for ; Wed, 15 Jan 2020 02:48:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0D7C24679 for ; Wed, 15 Jan 2020 02:48:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jSf0U8Oq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728877AbgAOCsh (ORCPT ); Tue, 14 Jan 2020 21:48:37 -0500 Received: from mail-pj1-f68.google.com ([209.85.216.68]:39142 "EHLO mail-pj1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728862AbgAOCsh (ORCPT ); Tue, 14 Jan 2020 21:48:37 -0500 Received: by mail-pj1-f68.google.com with SMTP id e11so5374786pjt.4; Tue, 14 Jan 2020 18:48:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=Sg5fwXgqypeNGg0cxshxZC3htmfkTgOsTSwPjyO8KRQ=; b=jSf0U8Oq1NHwfHbPcxjHWZJDCQiKzMJlXB+44XEvkicd1UEelGtlppjRzgl8aisFta zoNAal11qtUewecWoFqR+G1RykswiP/j247XR5CRkKlbvo29vgfVytKJmcVvLBbwn7K+ NJaEjUoawr6RgKbb1dt9AwhGTwO8ur2rR0F57JS3AwJAill2h/f7MtbYEP8g6Ny13Gi4 h2pFRz2rXoHjVirsMKzlPS1hDtTIvZhw4TTJDReo9zR4hI7VFIQnsitcm3rDx+lNxWo+ 3Y4ljlWjl1cy9hhqOp/wTv5bQCZp360eAfN0pB6Ee3QgwANxHA2zwn+E8U6Y5Q3RZGVB tiiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=Sg5fwXgqypeNGg0cxshxZC3htmfkTgOsTSwPjyO8KRQ=; b=TfTCNCk0ACDFuntim3ysvnzGsgbMhQok/4ROxOAPU/2FGLWMHBA9XiJ+k90zcN+ENe 4cYQvNoZ9ahA4P9xEkCIxV6HsbOCBMRI1rg012I53gGrrHnwbZRbrXxx5TzoR9mWYjpm KVAJYvTuAWWaffmcdOy25GK6CAomNVxdSX3DU2Ee+pOzuK69oBbWQgouDJT7V8frBFRZ uqpd3lN0HOuHeJ/rMfZR3DE20OFelW9pHQShEJgwanTZyf0bEFH1nCTqF0gkymxXWkh3 fZvBncLdqgHeGoOTNBLE+XDqYSjZTmTTzVjslu+v7BIaHVvqKD0FlnMyQ0/3EqcfRJmq Li8Q== X-Gm-Message-State: APjAAAW1f71bpB6+1hTX+3g++WA/kkcCOompec+O95hOXCCNqhO/3uqB 7Bi8E/Laq46UefxoZiRwSd8= X-Google-Smtp-Source: APXvYqzprJY/PXBVzlf3V6acMBTwUyrkNwszghAXBDVHCbqurohXr5NrtphwnRX50hsSrnYsWGJPsQ== X-Received: by 2002:a17:90b:f0f:: with SMTP id br15mr32499554pjb.138.1579056516270; Tue, 14 Jan 2020 18:48:36 -0800 (PST) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:180::cae7]) by smtp.gmail.com with ESMTPSA id c1sm20049859pfa.51.2020.01.14.18.48.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Jan 2020 18:48:35 -0800 (PST) Date: Tue, 14 Jan 2020 18:48:32 -0800 From: Alexei Starovoitov To: Stephen Smalley Cc: KP Singh , James Morris , Kees Cook , Casey Schaufler , open list , bpf , linux-security-module@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Thomas Garnier , Michael Halcrow , Paul Turner , Brendan Gregg , Jann Horn , Matthew Garrett , Christian Brauner , =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , Florent Revest , Brendan Jackman , Martin KaFai Lau , Song Liu , Yonghong Song , "Serge E. Hallyn" , Mauro Carvalho Chehab , "David S. Miller" , Greg Kroah-Hartman , Nicolas Ferre , Stanislav Fomichev , Quentin Monnet , Andrey Ignatov , Joe Stringer , Paul Moore Subject: Re: [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI) Message-ID: <20200115024830.4ogd3mi5jy5hwr2v@ast-mbp.dhcp.thefacebook.com> References: <20200109194302.GA85350@google.com> <8e035f4d-5120-de6a-7ac8-a35841a92b8a@tycho.nsa.gov> <20200110152758.GA260168@google.com> <20200110175304.f3j4mtach4mccqtg@ast-mbp.dhcp.thefacebook.com> <554ab109-0c23-aa82-779f-732d10f53d9c@tycho.nsa.gov> <49a45583-b4fb-6353-a8d4-6f49287b26eb@tycho.nsa.gov> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <49a45583-b4fb-6353-a8d4-6f49287b26eb@tycho.nsa.gov> User-Agent: NeoMutt/20180223 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Tue, Jan 14, 2020 at 12:42:22PM -0500, Stephen Smalley wrote: > On 1/14/20 11:54 AM, Stephen Smalley wrote: > > On 1/10/20 12:53 PM, Alexei Starovoitov wrote: > > > On Fri, Jan 10, 2020 at 04:27:58PM +0100, KP Singh wrote: > > > > On 09-Jan 14:47, Stephen Smalley wrote: > > > > > On 1/9/20 2:43 PM, KP Singh wrote: > > > > > > On 10-Jan 06:07, James Morris wrote: > > > > > > > On Thu, 9 Jan 2020, Stephen Smalley wrote: > > > > > > > > > > > > > > > On 1/9/20 1:11 PM, James Morris wrote: > > > > > > > > > On Wed, 8 Jan 2020, Stephen Smalley wrote: > > > > > > > > > > > > > > > > > > > The cover letter subject line and the > > > > > > > > > > Kconfig help text refer to it as a > > > > > > > > > > BPF-based "MAC and Audit policy".  It > > > > > > > > > > has an enforce config option that > > > > > > > > > > enables the bpf programs to deny access, > > > > > > > > > > providing access control. IIRC, > > > > > > > > > > in > > > > > > > > > > the earlier discussion threads, the BPF > > > > > > > > > > maintainers suggested that Smack > > > > > > > > > > and > > > > > > > > > > other LSMs could be entirely > > > > > > > > > > re-implemented via it in the future, and > > > > > > > > > > that > > > > > > > > > > such an implementation would be more optimal. > > > > > > > > > > > > > > > > > > In this case, the eBPF code is similar to a > > > > > > > > > kernel module, rather than a > > > > > > > > > loadable policy file.  It's a loadable > > > > > > > > > mechanism, rather than a policy, in > > > > > > > > > my view. > > > > > > > > > > > > > > > > I thought you frowned on dynamically loadable > > > > > > > > LSMs for both security and > > > > > > > > correctness reasons? > > > > > > > > > > > > Based on the feedback from the lists we've updated the design for v2. > > > > > > > > > > > > In v2, LSM hook callbacks are allocated dynamically using BPF > > > > > > trampolines, appended to a separate security_hook_heads and run > > > > > > only after the statically allocated hooks. > > > > > > > > > > > > The security_hook_heads for all the other LSMs (SELinux, AppArmor etc) > > > > > > still remains __lsm_ro_after_init and cannot be modified. We are still > > > > > > working on v2 (not ready for review yet) but the general idea can be > > > > > > seen here: > > > > > > > > > > > > https://github.com/sinkap/linux-krsi/blob/patch/v1/trampoline_prototype/security/bpf/lsm.c > > > > > > > > > > > > > > > > > > > > > > > > > > Evaluating the security impact of this is the next > > > > > > > step. My understanding > > > > > > > is that eBPF via BTF is constrained to read only access to hook > > > > > > > parameters, and that its behavior would be entirely restrictive. > > > > > > > > > > > > > > I'd like to understand the security impact more > > > > > > > fully, though. Can the > > > > > > > eBPF code make arbitrary writes to the kernel, or > > > > > > > read anything other than > > > > > > > the correctly bounded LSM hook parameters? > > > > > > > > > > > > > > > > > > > As mentioned, the BPF verifier does not allow writes to BTF types. > > > > > > > > > > > > > > And a traditional security module would necessarily fall > > > > > > > > under GPL; is the eBPF code required to be > > > > > > > > likewise?  If not, KRSI is a > > > > > > > > gateway for proprietary LSMs... > > > > > > > > > > > > > > Right, we do not want this to be a GPL bypass. > > > > > > > > > > > > This is not intended to be a GPL bypass and the BPF verifier checks > > > > > > for license compatibility of the loaded program with GPL. > > > > > > > > > > IIUC, it checks that the program is GPL compatible if it > > > > > uses a function > > > > > marked GPL-only.  But what specifically is marked GPL-only > > > > > that is required > > > > > for eBPF programs using KRSI? > > > > > > > > Good point! If no-one objects, I can add it to the BPF_PROG_TYPE_LSM > > > > specific verification for the v2 of the patch-set which would require > > > > all BPF-LSM programs to be GPL. > > > > > > I don't think it's a good idea to enforce license on the program. > > > The kernel doesn't do it for modules. > > > For years all of BPF tracing progs were GPL because they have to use > > > GPL-ed helpers to do anything meaningful. > > > So for KRSI just make sure that all helpers are GPL-ed as well. > > > > IIUC, the example eBPF code included in this patch series showed a > > program that used a GPL-only helper for the purpose of reporting event > > output to userspace. But it could have just as easily omitted the use of > > that helper and still implemented its own arbitrary access control model > > on the LSM hooks to which it attached.  It seems like the question is > > whether the kernel developers are ok with exposing the entire LSM hook > > interface and all the associated data structures to non-GPLd code, > > irrespective of what helpers it may or may not use. > > Also, to be clear, while kernel modules aren't necessarily GPL, prior to > this patch series, all Linux security modules were necessarily GPLd in order > to use the LSM interface. Because they use securityfs_create_file() GPL-ed api, right? but not because module license is enforced. > So allowing non-GPL eBPF-based LSMs would be a > change. I don't see it this way. seccomp progs technically unlicensed. Yet they can disallow any syscall. Primitive KRSI progs like int bpf-prog(void*) { return REJECT; } would be able to do selectively disable a syscall with an overhead acceptable in production systems (unlike seccomp). I want this use case to be available to people. It's a bait, because to do real progs people would need to GPL them. Key helpers bpf_perf_event_output, bpf_ktime_get_ns, bpf_trace_printk are all GPL-ed. It may look that most networking helpers are not-GPL, but real life is different. To debug programs bpf_trace_printk() is necessary. To have communication with user space bpf_perf_event_output() is necssary. To measure anything or implement timestamps bpf_ktime_get_ns() is necessary. So today all meaninful bpf programs are GPL. Those that are not GPL probably exist, but they're toy programs. Hence I have zero concerns about GPL bypass coming from tracing, networking, and, in the future, KRSI progs too.