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06 Nov 2018 11:22:05 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,472,1534834800"; d="scan'208";a="106403046" Received: from ray.jf.intel.com (HELO [10.7.201.133]) ([10.7.201.133]) by orsmga002.jf.intel.com with ESMTP; 06 Nov 2018 11:22:05 -0800 Subject: Re: RFC: userspace exception fixups To: Andy Lutomirski Cc: "Christopherson, Sean J" , 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: <20181102163034.GB7393@linux.intel.com> <7050972d-a874-dc08-3214-93e81181da60@intel.com> <20181102170627.GD7393@linux.intel.com> <20181102173350.GF7393@linux.intel.com> <20181102182712.GG7393@linux.intel.com> <20181102220437.GI7393@linux.intel.com> <1541518670.7839.31.camel@intel.com> <1541524750.7839.51.camel@intel.com> <22596E35-F5D1-4935-86AB-B510DCA0FABE@amacapital.net> 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 11/6/18 11:02 AM, Andy Lutomirski wrote: > On Tue, Nov 6, 2018 at 10:41 AM Dave Hansen wrote: >> >> On 11/6/18 10:20 AM, Andy Lutomirski wrote: >>> I almost feel like the right solution is to call into SGX on its own >>> private stack or maybe even its own private address space. >> >> Yeah, I had the same gut feeling. Couldn't the debugger even treat the >> enclave like its own "thread" with its own stack and its own set of >> registers and context? That seems like a much more workable model than >> trying to weave it together with the EENTER context. > > So maybe the API should be, roughly > > sgx_exit_reason_t sgx_enter_enclave(pointer_to_enclave, struct > host_state *state); > sgx_exit_reason_t sgx_resume_enclave(same args); > > where host_state is something like: > > struct host_state { > unsigned long bp, sp, ax, bx, cx, dx, si, di; > }; > > and the values in host_state explicitly have nothing to do with the > actual host registers. So, if you want to use the outcall mechanism, > you'd allocate some memory, point sp to that memory, call > sgx_enter_enclave(), and then read that memory to do the outcall. Ah, so instead of the enclave rudely "hijacking" the EENTER context, we have it nicely return and nicely _hint_ to the calling context what it would like to do. Then, the EENTER context can make a controlled transition over to the requested context. > Actually implementing this would be distinctly nontrivial, and would > almost certainly need some degree of kernel help to avoid an explosion > when a signal gets delivered while we have host_state.sp loaded into > the actual SP register. Maybe rseq could help with this? As long as the memory pointed to by host_state.sp is valid and can hold the signal frame (grows down without clobbering anything), what goes boom? The signal handling would push a signal frame and call the handler. It would have a shallow-looking stack, but the handler could just do its normal business and return from the signal where the frame would get popped and continue with %rsp=host_state.sp, blissfully unaware of the signal ever having happened.