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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 D5010C67839 for ; Tue, 11 Dec 2018 22:23:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A59802086D for ; Tue, 11 Dec 2018 22:23:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A59802086D 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 S1726243AbeLKWXP (ORCPT ); Tue, 11 Dec 2018 17:23:15 -0500 Received: from mga12.intel.com ([192.55.52.136]:47542 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726158AbeLKWXP (ORCPT ); Tue, 11 Dec 2018 17:23:15 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Dec 2018 14:23:14 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,343,1539673200"; d="scan'208";a="117998359" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.154]) by orsmga001.jf.intel.com with ESMTP; 11 Dec 2018 14:23:12 -0800 Date: Tue, 11 Dec 2018 14:23:12 -0800 From: Sean Christopherson To: Andy Lutomirski Cc: Josh Triplett , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , Jarkko Sakkinen , Dave Hansen , Peter Zijlstra , "H. Peter Anvin" , LKML , linux-sgx@vger.kernel.org, Haitao Huang , Jethro Beekman , "Dr. Greg Wettstein" Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU Message-ID: <20181211222312.GI14731@linux.intel.com> References: <20181210232141.5425-1-sean.j.christopherson@intel.com> <20181210232449.GA11843@localhost> <20181211165253.GB14731@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Tue, Dec 11, 2018 at 09:58:19AM -0800, Andy Lutomirski wrote: > > On Dec 11, 2018, at 8:52 AM, Sean Christopherson wrote: > > > >> On Tue, Dec 11, 2018 at 07:41:27AM -0800, Andy Lutomirski wrote: > >> > >> > >>>> On Dec 10, 2018, at 3:24 PM, Josh Triplett wrote: > >>>> > >>>> On Mon, Dec 10, 2018 at 03:21:37PM -0800, Sean Christopherson wrote: > >>>> At that point I realized it's a hell of a lot easier to simply provide > >>>> an IOCTL via /dev/sgx that allows userspace to register a per-process > >>>> ENCLU exception handler. At a high level, the basic idea is the same > >>>> as the vDSO approach: provide a hardcoded fixup handler for ENCLU and > >>>> attempt to fixup select unhandled exceptions that occurred in user code. > >>> > >>> So, on the one hand, this is *absolutely* much cleaner than the VDSO > >>> approach. On the other hand, this is global process state and has some > >>> of the same problems as a signal handler as a result. > >> > >> I liked the old version better for this reason > > > > This isn't fundamentally different than forcing all EENTER calls through > > the vDSO, which is also per-process. Technically this is more flexible > > in that regard since userspace gets to choose where their one ENCLU gets > > to reside. Userspace can have per-enclave entry flows so long as the > > actual ENLU[EENTER] is common, same as vDSO. > > Right. The problem is that user libraries have a remarkably hard time > agreeing on where their one copy of anything lives. Are you concerned about userspace shooting themselves in the foot, e.g. unknowingly overwriting their handler? Requiring unregister->register to change the handler would mitigate that issue for the most part. Or we could even say it's a write-once property. That obviously doesn't solve the issue of a userspace application deliberately using two different libraries to run enclaves in a single process, but I have a hard time envisioning a scenario where someone would want to use two different *SGX* libraries in a single process. Don't most of the signal issue arise due to loading multiple libraries that provide *different* services needing to handle signals?