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 102C2C433DB for ; Mon, 1 Feb 2021 22:43:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9D01864ECC for ; Mon, 1 Feb 2021 22:43:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9D01864ECC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 001546B0005; Mon, 1 Feb 2021 17:43:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EF3196B0006; Mon, 1 Feb 2021 17:43:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DBB4B6B006E; Mon, 1 Feb 2021 17:43:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0213.hostedemail.com [216.40.44.213]) by kanga.kvack.org (Postfix) with ESMTP id C310E6B0005 for ; Mon, 1 Feb 2021 17:43:46 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 8D3091EF1 for ; Mon, 1 Feb 2021 22:43:46 +0000 (UTC) X-FDA: 77771177652.23.swim26_5012a75275c5 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id 719BC37604 for ; Mon, 1 Feb 2021 22:43:46 +0000 (UTC) X-HE-Tag: swim26_5012a75275c5 X-Filterd-Recvd-Size: 4334 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by imf45.hostedemail.com (Postfix) with ESMTP for ; Mon, 1 Feb 2021 22:43:44 +0000 (UTC) IronPort-SDR: qQnKlDRyZuWfaVh6+r1uX09r7yAezSSDrT3DU1g6Dpez5iISWrwZcGqEEiwg56JVoyito1oPyv rKMVHpoN3jZA== X-IronPort-AV: E=McAfee;i="6000,8403,9882"; a="265595908" X-IronPort-AV: E=Sophos;i="5.79,393,1602572400"; d="scan'208";a="265595908" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Feb 2021 14:43:38 -0800 IronPort-SDR: +5l2L9vjp3HQMsKOzhT+l3CRrMTSzFU8RUybBz3j5N9a3Cn8AWHt3EseUFqtx4p+5iA57Tx60k vxIueP/VCVjA== X-IronPort-AV: E=Sophos;i="5.79,393,1602572400"; d="scan'208";a="370141421" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.112.229]) ([10.212.112.229]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Feb 2021 14:43:37 -0800 Subject: Re: [PATCH v18 05/25] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states To: Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Andrew Cooper References: <20210127212524.10188-1-yu-cheng.yu@intel.com> <20210127212524.10188-6-yu-cheng.yu@intel.com> <7793b36e-6386-3f2e-36ca-b7ca988a88c9@intel.com> <43f264df-2f3a-ea4c-c737-85cdc6714bd8@intel.com> <0a5a80c0-afc7-5f91-9e28-a300e30f1ab3@intel.com> From: "Yu, Yu-cheng" Message-ID: <465836bd-9c80-fed9-d9af-89275ff810eb@intel.com> Date: Mon, 1 Feb 2021 14:43:33 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <0a5a80c0-afc7-5f91-9e28-a300e30f1ab3@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/29/2021 2:53 PM, Dave Hansen wrote: > On 1/29/21 2:35 PM, Yu, Yu-cheng wrote: >>> Andy Cooper just mentioned on IRC about this nugget in the spec: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0XRSTORS on CET state will do reserved bit an= d canonicality >>> =C2=A0=C2=A0=C2=A0=C2=A0checks on the state in similar manner as don= e by the WRMSR to >>> =C2=A0=C2=A0=C2=A0=C2=A0these state elements. >>> >>> We're using copy_kernel_to_xregs_err(), so the #GP *should* be OK. >>> Could we prove this out in practice, please? >>>> >> Do we want to verify that setting reserved bits in CET XSAVES states >> triggers GP?=C2=A0 Then, yes, I just verified it again.=C2=A0 Thanks f= or >> reminding.=C2=A0 Do we have any particular case relating to this? >=20 > I want to confirm that it triggers #GP and kills userspace without the > kernel WARN'ing or otherwise being visibly unhappy. For sigreturn, shadow stack pointer is checked against its restore token=20 and must be smaller than TASK_SIZE_MAX. Sigreturn cannot set any=20 MSR_IA32_U_CET reserved bits. >=20 > What about the return-to-userspace path after a ptracer writes content > to the CET fields? I don't see the same tolerance for errors in > __fpregs_load_activate(), for instance. >=20 Good thought. I have not sent out my revised PTRACE patch, but values=20 from user will be checked for valid address and reserved bits. -- Yu-cheng