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08 Nov 2018 12:10:31 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,480,1534834800"; d="scan'208";a="106622477" Received: from ray.jf.intel.com (HELO [10.7.201.15]) ([10.7.201.15]) by orsmga001.jf.intel.com with ESMTP; 08 Nov 2018 12:10:30 -0800 Subject: Re: RFC: userspace exception fixups To: Andy Lutomirski , "Christopherson, Sean J" Cc: 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 References: <1541518670.7839.31.camel@intel.com> <1541524750.7839.51.camel@intel.com> <22596E35-F5D1-4935-86AB-B510DCA0FABE@amacapital.net> <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> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. We could quite easily have the untrusted code just promise to allocate a stack-sized virtual area (even derived from the stack rlimit size) and pass that into the enclave for parameter use.