From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Subject: Re: RFC: userspace exception fixups Date: Thu, 8 Nov 2018 14:04:16 -0800 Message-ID: <20181108220416.GA18263@linux.intel.com> References: <1C426267-492F-4AE7-8BE8-C7FE278531F9@amacapital.net> <209cf4a5-eda9-2495-539f-fed22252cf02@intel.com> <9B76E95B-5745-412E-8007-7FAA7F83D6FB@amacapital.net> <20181108195420.GA14715@linux.intel.com> <7027c3dc-addb-1b96-027e-a57fccf1f812@intel.com> <20181108211600.GA17167@linux.intel.com> <7d965299-0402-f730-6e1a-515a836a3956@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <7d965299-0402-f730-6e1a-515a836a3956@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Dave Hansen Cc: Andy Lutomirski , Andrew Lutomirski , Jann Horn , Linus Torvalds , Rich Felker , Dave Hansen , Jethro Beekman , Jarkko Sakkinen , Florian Weimer , Linux API , X86 ML , linux-arch , LKML , Peter Zijlstra , nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" , shay.katz-zamir@intel.com, linux-sgx@vger.kernel.org, Andy Shevchenko , Thomas Gleixner List-Id: linux-arch.vger.kernel.org On Thu, Nov 08, 2018 at 01:50:31PM -0800, Dave Hansen wrote: > On 11/8/18 1:16 PM, Sean Christopherson wrote: > > On Thu, Nov 08, 2018 at 12:10:30PM -0800, Dave Hansen wrote: > >> On 11/8/18 12:05 PM, Andy Lutomirski wrote: > >>> Hmm. The idea being that the SDK preserves RBP but not RSP. That's > >>> not the most terrible thing in the world. But could the SDK live with > >>> something more like my suggestion where the vDSO supplies a normal > >>> function that takes a struct containing registers that are visible to > >>> the enclave? This would make it extremely awkward for the enclave to > >>> use the untrusted stack per se, but it would make it quite easy (I > >>> think) for the untrusted part of the SDK to allocate some extra memory > >>> and just tell the enclave that *that* memory is the stack. > >> > >> I really think the enclave should keep its grubby mitts off the > >> untrusted stack. There are lots of ways to get memory, even with > >> stack-like semantics, that don't involve mucking with the stack itself. > >> > >> I have not heard a good, hard argument for why there is an absolute > >> *need* to store things on the actual untrusted stack. > > > > Convenience and performance are the only arguments I've heard, e.g. so > > that allocating memory doesn't require an extra EEXIT->EENTER round trip. > > Well, for the first access, it's going to cost a bunch asynchronous > exits to fault in all the stack pages. Instead of that, if you had a > single area, or an explicit out-call to allocate and populate the area, > you could do it in a single EEXIT and zero asynchronous exits for demand > page faults. > > So, it might be convenient, but I'm rather suspicious of any performance > arguments. Ya, I meant versus doing an EEXIT on every allocation, i.e. a very naive allocation scheme. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga03.intel.com ([134.134.136.65]:46002 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730305AbeKIHls (ORCPT ); Fri, 9 Nov 2018 02:41:48 -0500 Date: Thu, 8 Nov 2018 14:04:16 -0800 From: Sean Christopherson Subject: Re: RFC: userspace exception fixups Message-ID: <20181108220416.GA18263@linux.intel.com> References: <1C426267-492F-4AE7-8BE8-C7FE278531F9@amacapital.net> <209cf4a5-eda9-2495-539f-fed22252cf02@intel.com> <9B76E95B-5745-412E-8007-7FAA7F83D6FB@amacapital.net> <20181108195420.GA14715@linux.intel.com> <7027c3dc-addb-1b96-027e-a57fccf1f812@intel.com> <20181108211600.GA17167@linux.intel.com> <7d965299-0402-f730-6e1a-515a836a3956@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7d965299-0402-f730-6e1a-515a836a3956@intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Hansen Cc: Andy Lutomirski , Andrew Lutomirski , Jann Horn , Linus Torvalds , Rich Felker , Dave Hansen , Jethro Beekman , Jarkko Sakkinen , Florian Weimer , Linux API , X86 ML , linux-arch , LKML , Peter Zijlstra , nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" , shay.katz-zamir@intel.com, linux-sgx@vger.kernel.org, Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Carlos O'Donell , adhemerval.zanella@linaro.org Message-ID: <20181108220416.fnTE6_zFk2pfbcq_W4nysx4KvoxTgDrGP7DvGgDx9k0@z> On Thu, Nov 08, 2018 at 01:50:31PM -0800, Dave Hansen wrote: > On 11/8/18 1:16 PM, Sean Christopherson wrote: > > On Thu, Nov 08, 2018 at 12:10:30PM -0800, Dave Hansen wrote: > >> On 11/8/18 12:05 PM, Andy Lutomirski wrote: > >>> Hmm. The idea being that the SDK preserves RBP but not RSP. That's > >>> not the most terrible thing in the world. But could the SDK live with > >>> something more like my suggestion where the vDSO supplies a normal > >>> function that takes a struct containing registers that are visible to > >>> the enclave? This would make it extremely awkward for the enclave to > >>> use the untrusted stack per se, but it would make it quite easy (I > >>> think) for the untrusted part of the SDK to allocate some extra memory > >>> and just tell the enclave that *that* memory is the stack. > >> > >> I really think the enclave should keep its grubby mitts off the > >> untrusted stack. There are lots of ways to get memory, even with > >> stack-like semantics, that don't involve mucking with the stack itself. > >> > >> I have not heard a good, hard argument for why there is an absolute > >> *need* to store things on the actual untrusted stack. > > > > Convenience and performance are the only arguments I've heard, e.g. so > > that allocating memory doesn't require an extra EEXIT->EENTER round trip. > > Well, for the first access, it's going to cost a bunch asynchronous > exits to fault in all the stack pages. Instead of that, if you had a > single area, or an explicit out-call to allocate and populate the area, > you could do it in a single EEXIT and zero asynchronous exits for demand > page faults. > > So, it might be convenient, but I'm rather suspicious of any performance > arguments. Ya, I meant versus doing an EEXIT on every allocation, i.e. a very naive allocation scheme.