From mboxrd@z Thu Jan 1 00:00:00 1970 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" , , , "Ayoun, Serge" , , , Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "Carlos O'Donell" , 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 Message-ID: Date: Tue, 6 Nov 2018 11:22:05 -0800 In-Reply-To: Content-Type: text/plain; charset="utf-8" Return-Path: dave.hansen@intel.com MIME-Version: 1.0 List-ID: 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. 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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 C9F7EC32789 for ; Tue, 6 Nov 2018 19:22:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 956E62085B for ; Tue, 6 Nov 2018 19:22:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 956E62085B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-sgx-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388227AbeKGEsu (ORCPT ); Tue, 6 Nov 2018 23:48:50 -0500 Received: from mga05.intel.com ([192.55.52.43]:6971 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387862AbeKGEsu (ORCPT ); Tue, 6 Nov 2018 23:48:50 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 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-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org Message-ID: <20181106192205.R6tdR-MZBuTv2Y6cuairv1ZsHe6QZUgCWjrJfnq0X2c@z> 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.