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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 6402DC31E45 for ; Fri, 14 Jun 2019 00:46:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 425F220850 for ; Fri, 14 Jun 2019 00:46:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726455AbfFNAqC (ORCPT ); Thu, 13 Jun 2019 20:46:02 -0400 Received: from mga11.intel.com ([192.55.52.93]:18675 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725778AbfFNAqC (ORCPT ); Thu, 13 Jun 2019 20:46:02 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Jun 2019 17:46:01 -0700 X-ExtLoop1: 1 Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.36]) by fmsmga007.fm.intel.com with ESMTP; 13 Jun 2019 17:46:00 -0700 Date: Thu, 13 Jun 2019 17:46:00 -0700 From: Sean Christopherson To: Stephen Smalley Cc: Cedric Xing , linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org, jarkko.sakkinen@linux.intel.com, luto@kernel.org, jmorris@namei.org, serge@hallyn.com, paul@paul-moore.com, eparis@parisplace.org, jethro@fortanix.com, dave.hansen@intel.com, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, nhorman@redhat.com, pmccallum@redhat.com, serge.ayoun@intel.com, shay.katz-zamir@intel.com, haitao.huang@intel.com, andriy.shevchenko@linux.intel.com, kai.svahn@intel.com, bp@alien8.de, josh@joshtriplett.org, kai.huang@intel.com, rientjes@google.com, william.c.roberts@intel.com, philip.b.tricca@intel.com Subject: Re: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux Message-ID: <20190614004600.GF18385@linux.intel.com> References: <20190611220243.GB3416@linux.intel.com> <8d99d8fb-a921-286a-8cf0-cd522e09b37c@tycho.nsa.gov> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d99d8fb-a921-286a-8cf0-cd522e09b37c@tycho.nsa.gov> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Thu, Jun 13, 2019 at 01:02:17PM -0400, Stephen Smalley wrote: > On 6/11/19 6:02 PM, Sean Christopherson wrote: > >On Tue, Jun 11, 2019 at 09:40:25AM -0400, Stephen Smalley wrote: > >>I haven't looked at this code closely, but it feels like a lot of > >>SGX-specific logic embedded into SELinux that will have to be repeated or > >>reused for every security module. Does SGX not track this state itself? > > > >SGX does track equivalent state. > > > >There are three proposals on the table (I think): > > > > 1. Require userspace to explicitly specificy (maximal) enclave page > > permissions at build time. The enclave page permissions are provided > > to, and checked by, LSMs at enclave build time. > > > > Pros: Low-complexity kernel implementation, straightforward auditing > > Cons: Sullies the SGX UAPI to some extent, may increase complexity of > > SGX2 enclave loaders. > > > > 2. Pre-check LSM permissions and dynamically track mappings to enclave > > pages, e.g. add an SGX mprotect() hook to restrict W->X and WX > > based on the pre-checked permissions. > > > > Pros: Does not impact SGX UAPI, medium kernel complexity > > Cons: Auditing is complex/weird, requires taking enclave-specific > > lock during mprotect() to query/update tracking. > > > > 3. Implement LSM hooks in SGX to allow LSMs to track enclave regions > > from cradle to grave, but otherwise defer everything to LSMs. > > > > Pros: Does not impact SGX UAPI, maximum flexibility, precise auditing > > Cons: Most complex and "heaviest" kernel implementation of the three, > > pushes more SGX details into LSMs. > > > >My RFC series[1] implements #1. My understanding is that Andy (Lutomirski) > >prefers #2. Cedric's RFC series implements #3. > > > >Perhaps the easiest way to make forward progress is to rule out the > >options we absolutely *don't* want by focusing on the potentially blocking > >issue with each option: > > > > #1 - SGX UAPI funkiness > > > > #2 - Auditing complexity, potential enclave lock contention > > > > #3 - Pushing SGX details into LSMs and complexity of kernel implementation > > > > > >[1] https://lkml.kernel.org/r/20190606021145.12604-1-sean.j.christopherson@intel.com > > Given the complexity tradeoff, what is the clear motivating example for why > #1 isn't the obvious choice? That the enclave loader has no way of knowing a > priori whether the enclave will require W->X or WX? But aren't we better > off requiring enclaves to be explicitly marked as needing such so that we > can make a more informed decision about whether to load them in the first > place? Andy and/or Cedric, can you please weigh in with a concrete (and practical) use case that will break if we go with #1? The auditing issues for #2/#3 are complex to say the least...