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=-1.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 EE90EC07E85 for ; Tue, 11 Dec 2018 17:58:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B65D020855 for ; Tue, 11 Dec 2018 17:58:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544551115; bh=IT+/Sn539b1Hv8g6PSWkXhUMKvsM5oSYYLuIqhpavcs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=kOFerPOGQzPScrJqOM7bx1dGdQh/nfvYDgeSJh3bU5xkioEJWvp7TkTatca8Oxzz+ 2D/ij8/DqL2Oia+MdHOq5BbqjtjlfSlUtt9dWTHnWdvGlm7LdkLEjPeGAtYZ0TySUW cDHge8NzACxPu5ZyDLYsMRIM/nR64Muy7+jkx74g= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B65D020855 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726775AbeLKR6e (ORCPT ); Tue, 11 Dec 2018 12:58:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:46976 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726485AbeLKR6e (ORCPT ); Tue, 11 Dec 2018 12:58:34 -0500 Received: from mail-wm1-f46.google.com (mail-wm1-f46.google.com [209.85.128.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0321F208E7 for ; Tue, 11 Dec 2018 17:58:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544551113; bh=IT+/Sn539b1Hv8g6PSWkXhUMKvsM5oSYYLuIqhpavcs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=KzPMVCIasypCyr/lG9ew7dulA9cm+XNoq7h1/vatjcUMLSWnwovRqtB0FCoa9oEG+ 3sNT2Kd29o/3Mlbbll7HAaSHlJc+55hE+ERi8s9Rl20c2d3cpdVv3DC5oROgbT6dq+ Yo241SoQrwAjqZQZULXXHnxfRs+NI30mhvrlsKD8= Received: by mail-wm1-f46.google.com with SMTP id m22so3263765wml.3 for ; Tue, 11 Dec 2018 09:58:32 -0800 (PST) X-Gm-Message-State: AA+aEWZjJH3r50xQPDMtDVUZAzBiLVp7umzahiQXq17lfRh6xSuLKnKz tV5OTVt7uUYnlf8W8akSurzYqvvfcWddiYPBSbQ4jA== X-Google-Smtp-Source: AFSGD/VZqjpsAKbB53VjIJvHUw8HgLmuFtHxraUUCrmVWwQsuDerPo/JeZR7SnVU9e2mbHYCy63hBJUbTsU5dCMewtk= X-Received: by 2002:a1c:aa0f:: with SMTP id t15mr3219252wme.108.1544551111470; Tue, 11 Dec 2018 09:58:31 -0800 (PST) MIME-Version: 1.0 References: <20181210232141.5425-1-sean.j.christopherson@intel.com> <20181210232449.GA11843@localhost> <20181211165253.GB14731@linux.intel.com> In-Reply-To: <20181211165253.GB14731@linux.intel.com> From: Andy Lutomirski Date: Tue, 11 Dec 2018 09:58:19 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU To: "Christopherson, Sean J" Cc: Josh Triplett , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , Jarkko Sakkinen , Dave Hansen , Andrew Lutomirski , Peter Zijlstra , "H. Peter Anvin" , LKML , linux-sgx@vger.kernel.org, Haitao Huang , Jethro Beekman , "Dr. Greg Wettstein" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > 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 wro= te: >>>> >>>> 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 cod= e. >>> >>> 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. > >> and for another reason: >> while this new one looks very very simple, it still has the hidden >> complexity that the magic values written to registers in the event of an >> exception are very much Linux specific. > > Definitely more magical, but not necessarily more difficult to document. > It'd essentially be an extension of hardware's AEE/AEP behavior. > >> OTOH, the old approach clobbered more regs than needed, but that=E2=80= =99s a easy fix.