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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 52133C11F67 for ; Tue, 29 Jun 2021 19:27:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 35C2861DE3 for ; Tue, 29 Jun 2021 19:27:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232866AbhF2T32 (ORCPT ); Tue, 29 Jun 2021 15:29:28 -0400 Received: from mga09.intel.com ([134.134.136.24]:63786 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232116AbhF2T31 (ORCPT ); Tue, 29 Jun 2021 15:29:27 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10030"; a="208168663" X-IronPort-AV: E=Sophos;i="5.83,309,1616482800"; d="scan'208";a="208168663" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2021 12:26:58 -0700 X-IronPort-AV: E=Sophos;i="5.83,309,1616482800"; d="scan'208";a="643830001" Received: from bzhang2-mobl1.amr.corp.intel.com (HELO [10.255.231.86]) ([10.255.231.86]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2021 12:26:57 -0700 Subject: Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state To: "Bae, Chang Seok" Cc: "Lutomirski, Andy" , Borislav Petkov , Thomas Gleixner , Ingo Molnar , X86 ML , "Brown, Len" , "Liu, Jing2" , "Shankar, Ravi V" , LKML References: <20210523193259.26200-1-chang.seok.bae@intel.com> <20210523193259.26200-15-chang.seok.bae@intel.com> <872cb0a2-3659-2e6c-52a8-33f1a2f0a2cd@kernel.org> <36D0486A-D955-4C32-941A-A2A4985A450C@intel.com> <48e86785-838d-f5d4-c93c-3232b8ffd915@intel.com> <3AB6DECB-2A53-4EC2-84A6-0CACE44CFC1C@intel.com> <6754330a-bbbb-aa29-7800-f2d16216ad8c@intel.com> <406DB587-F598-484F-A128-990E2DB6EC78@intel.com> <842d8e8a-44c6-a8c5-c580-a77fc52d267f@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/29/21 12:13 PM, Bae, Chang Seok wrote: >> >> Is it actually important to make sure that they are dynamic features? >> Is there *any* case where a feature (dynamic or not) can have XFD armed >> and be out of its init state? > In this AMX series, XFD is only used for the xstate buffer management. The > code is made in a such way that XFD and dynamic states are a bit coupled. > > But I think XFD can be extended for other usages in the future. Then, yes. > (This warning is also for future code changes.) > > So, reading the MSR is just simple and clean here, but it consumes cycles. Or, > a task may have a field for XFD value per se unless this conversion is > acceptable. I'm not following. All that I see here is that you made what could be a very generic check: Thou shalt never XSAVE a xfeature which is XFD-armed and made it more specific: Thou shalt never XSAVE a *dynamic* xfeature which is XFD-armed I'm just saying that I don't see the value in a less-broad check. Let's make the sanity check as broad as possible. That actually makes the code simpler.