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=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 58BD3C31E4A for ; Thu, 13 Jun 2019 17:00:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B307206BB for ; Thu, 13 Jun 2019 17:00:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730026AbfFMQ7r convert rfc822-to-8bit (ORCPT ); Thu, 13 Jun 2019 12:59:47 -0400 Received: from mga06.intel.com ([134.134.136.31]:22262 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729804AbfFMAKj (ORCPT ); Wed, 12 Jun 2019 20:10:39 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jun 2019 17:10:38 -0700 X-ExtLoop1: 1 Received: from orsmsx103.amr.corp.intel.com ([10.22.225.130]) by fmsmga008.fm.intel.com with ESMTP; 12 Jun 2019 17:10:38 -0700 Received: from orsmsx116.amr.corp.intel.com ([169.254.7.166]) by ORSMSX103.amr.corp.intel.com ([169.254.5.232]) with mapi id 14.03.0415.000; Wed, 12 Jun 2019 17:10:37 -0700 From: "Xing, Cedric" To: "Christopherson, Sean J" , "Andy Lutomirski" CC: Stephen Smalley , LSM List , "selinux@vger.kernel.org" , LKML , "linux-sgx@vger.kernel.org" , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Paul Moore , Eric Paris , Jethro Beekman , "Hansen, Dave" , Thomas Gleixner , Linus Torvalds , Andrew Morton , "nhorman@redhat.com" , "pmccallum@redhat.com" , "Ayoun, Serge" , "Katz-zamir, Shay" , "Huang, Haitao" , Andy Shevchenko , "Svahn, Kai" , Borislav Petkov , Josh Triplett , "Huang, Kai" , David Rientjes , "Roberts, William C" , "Tricca, Philip B" Subject: RE: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux Thread-Topic: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux Thread-Index: AQHVH1ilvNGS2ZisK0eWTCWidam/YaaW7RmAgACMWICAAWfBAIAAKpIA//+YzvA= Date: Thu, 13 Jun 2019 00:10:37 +0000 Message-ID: <960B34DE67B9E140824F1DCDEC400C0F65503261@ORSMSX116.amr.corp.intel.com> References: <20190611220243.GB3416@linux.intel.com> <20190612220242.GJ20308@linux.intel.com> In-Reply-To: <20190612220242.GJ20308@linux.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiMDhmOWQxYWItZGYxOC00NDE5LWI5YmQtMjdkNDE0ZTdmYjVmIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoiYmM4cGFEMU03UU9yd1pLVSs0bEU5czk2RUNacmxySk1RU2w5b1puWjlWTkRIQ3BLdnZJeEVoa1VsTHdMV2pJMiJ9 x-ctpclassification: CTP_NT dlp-product: dlpe-windows dlp-version: 11.2.0.6 dlp-reaction: no-action x-originating-ip: [10.22.254.138] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: > From: Christopherson, Sean J > Sent: Wednesday, June 12, 2019 3:03 PM > > > I think this model works quite well in an SGX1 world. The main thing > > that makes me uneasy about this model is that, in SGX2, it requires > > that an SGX2-compatible enclave loader must pre-declare to the kernel > > whether it intends for its dynamically allocated memory to be > > ALLOW_EXEC. If ALLOW_EXEC is set but not actually needed, it will > > still fail if DENY_X_IF_ALLOW_WRITE ends up being set. The other > > version below does not have this limitation. > > I'm not convinced this will be a meaningful limitation in practice, > though that's probably obvious from my RFCs :-). That being said, the > UAPI quirk is essentially a dealbreaker for multiple people, so let's > drop #1. > > I discussed the options with Cedric offline, and he is ok with option #2 > *if* the idea actually translates to acceptable code and doesn't present > problems for userspace and/or future SGX features. > > So, I'll work on an RFC series to implement #2 as described below. If > it works out, yay! If not, i.e. option #2 is fundamentally broken, I'll > shift my focus to Cedric's code (option #3). > > > > 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. > > > > Here's how this looks in my mind. It's quite similar, except that > > ALLOW_READ, ALLOW_WRITE, and ALLOW_EXEC are replaced with a little > > state machine. > > > > EADD does not take any special flags. It calls this LSM hook: > > > > int security_enclave_load(struct vm_area_struct *source); > > > > This hook can return -EPERM. Otherwise it 0 or > > ALLOC_EXEC_IF_UNMODIFIED (i.e. 1). This hook enforces permissions (a) > and (b). > > > > The driver tracks a state for each page, and the possible states are: > > > > - CLEAN_MAYEXEC /* no W or X VMAs have existed, but X is okay */ > > - CLEAN_NOEXEC /* no W or X VMAs have existed, and X is not okay */ > > - CLEAN_EXEC /* no W VMA has existed, but an X VMA has existed */ > > - DIRTY /* a W VMA has existed */ > > > > The initial state for a page is CLEAN_MAYEXEC if the hook said > > ALLOW_EXEC_IF_UNMODIFIED and CLEAN_NOEXEC otherwise. > > > > The future EAUG does not call a hook at all and puts pages into the > > state CLEAN_NOEXEC. If SGX3 or later ever adds EAUG-but-don't-clear, > > it can call security_enclave_load() and add CLEAN_MAYEXEC pages if > appropriate. > > > > EINIT takes a sigstruct pointer. SGX calls a new hook: > > > > unsigned int security_enclave_init(struct sigstruct *sigstruct, > > struct vm_area_struct *source, unsigned int flags); > > > > This hook can return -EPERM. Otherwise it returns 0 or a combination > > of flags DENY_WX and DENY_X_DIRTY. The driver saves this value. > > These represent permissions (c) and (d). > > > > If we want to have a permission for "execute code supplied from > > outside the enclave that was not measured", we could have a flag like > > HAS_UNMEASURED_CLEAN_EXEC_PAGE that the LSM could consider. > > > > mmap() and mprotect() enforce the following rules: > > > > - If VM_EXEC is requested and (either the page is DIRTY or VM_WRITE > is > > requested) and DENY_X_DIRTY, then deny. > > > > - If VM_WRITE and VM_EXEC are both requested and DENY_WX, then deny. > > > > - If VM_WRITE is requested, we need to update the state. If it was > > CLEAN_EXEC, then we reject if DENY_X_DIRTY. Otherwise we change > the > > state to DIRTY. > > > > - If VM_EXEC is requested and the page is CLEAN_NOEXEC, then deny. > > > > mprotect() and mmap() do *not* call SGX-specific LSM hooks to ask for > > permission, although they can optionally call an LSM hook if they hit > > one of the -EPERM cases for auditing purposes. > > > > Before the SIGSTRUCT is provided to the driver, the driver acts as > > though DENY_X_DIRTY and DENY_WX are both set. I think we've been discussing 2 topics simultaneously, one is the state machine that accepts/rejects mmap/mprotect requests, while the other is where is the best place to put it. I think we have an agreement on the former, and IMO option #2 and #3 differ only in the latter. Option #2 keeps the state machine inside SGX subsystem, so it could reuse existing data structures for page tracking/locking to some extent. Sean may have smarter ideas, but it looks to me like the existing 'struct sgx_encl_page' tracks individual enclave pages while the FSM states apply to ranges. So in order *not* to test page by page in mmap/mprotect, I guess some new range oriented structures are still necessary. But I don't think it very important anyway. My major concern is more from the architecture/modularity perspective. Specifically, the state machine is defined by LSM but SGX does the state transitions. That's a brittle relationship that'd break easily if the state machine changes in future, or if different LSM modules want to define different FSMs (comprised of different set of states and/or triggers). After all, what's needed by the SGX subsystem is just the decision, not the FSM definition. I think we should take a closer look at this area once Sean's patch comes out.