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 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 8575EC32789 for ; Tue, 6 Nov 2018 17:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DBB32081D for ; Tue, 6 Nov 2018 17:00:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4DBB32081D 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 S2389449AbeKGC0q (ORCPT ); Tue, 6 Nov 2018 21:26:46 -0500 Received: from mga05.intel.com ([192.55.52.43]:59686 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389285AbeKGC0q (ORCPT ); Tue, 6 Nov 2018 21:26:46 -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 09:00:38 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,472,1534834800"; d="scan'208";a="106367061" 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 09:00:38 -0800 Subject: Re: RFC: userspace exception fixups To: Sean Christopherson , Andy Lutomirski , Jann Horn Cc: 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> 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: <1541518670.7839.31.camel@intel.com> 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: <20181106170038.0r5i5joo_2vpgdDepp2yg7PfnT9smuBw5XA0NJ93JnM@z> On 11/6/18 7:37 AM, Sean Christopherson wrote: > > void *sgx_alloc_untrusted_stack(size_t size) > { > struct sgx_encl_tls *tls = get_encl_tls(); > struct sgx_out_call_context *context; > void *tmp; > > /* create a frame on the trusted stack to hold the out-call context */ > tls->trusted_stack -= sizeof(struct sgx_out_call_context); > > /* save the untrusted %RSP into the out-call context */ > context = (struct sgx_out_call_context *)tls->trusted_stack; > context->untrusted_stack = tls->save_state_area[SSA_RSP]; > > /* allocate space on the untrusted stack */ > tmp = (void *)(tls->save_state_area[SSA_RSP] - size); > tls->save_state_area[SSA_RSP] = tmp; > > return tmp; > } Why does it bother to go to all the trouble of mucking with the untrusted stack? It could *easily* just leave it alone and do out-calls if it needs to allocate memory for parameter storage. Heck, that could theoretically even be _on_ the stack if the untrusted runtime was being clever. The only downside would be that the untrusted runtime would have to keep track of the space a bit more explicitly so it could be cleaned up if the enclave didn't do it.