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=-5.4 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 B626DC433DB for ; Wed, 3 Feb 2021 21:54:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 264D264F5F for ; Wed, 3 Feb 2021 21:54:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 264D264F5F 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 771636B006E; Wed, 3 Feb 2021 16:54:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 721546B0070; Wed, 3 Feb 2021 16:54:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5E9F86B0071; Wed, 3 Feb 2021 16:54:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0192.hostedemail.com [216.40.44.192]) by kanga.kvack.org (Postfix) with ESMTP id 3E12A6B006E for ; Wed, 3 Feb 2021 16:54:47 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E69BE3624 for ; Wed, 3 Feb 2021 21:54:46 +0000 (UTC) X-FDA: 77778311772.12.hate10_0610765275d6 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id BF1711801B740 for ; Wed, 3 Feb 2021 21:54:46 +0000 (UTC) X-HE-Tag: hate10_0610765275d6 X-Filterd-Recvd-Size: 4566 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Wed, 3 Feb 2021 21:54:44 +0000 (UTC) IronPort-SDR: a7dcWmGjpSc1AKkdRh4imLMUl+mUbZMDuQW9V9pyWOVbxDgDBb48CKuuSOrY1T2iKebwrspzWt QQo5Z5X4UU8g== X-IronPort-AV: E=McAfee;i="6000,8403,9884"; a="200093594" X-IronPort-AV: E=Sophos;i="5.79,399,1602572400"; d="scan'208";a="200093594" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Feb 2021 13:54:43 -0800 IronPort-SDR: cbNFcluLVt0agMFYdYPy9R/OKBGP7PxtHIJxAE2sR0GRhutjiRbmm0lsH8LRWO3x3Iolq9fwYN AW0O5oc+YcIA== X-IronPort-AV: E=Sophos;i="5.79,399,1602572400"; d="scan'208";a="433627376" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.43.162]) ([10.212.43.162]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Feb 2021 13:54:41 -0800 Subject: Re: [PATCH v18 24/25] x86/cet/shstk: Add arch_prctl functions for shadow stack From: "Yu, Yu-cheng" 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 References: <20210127212524.10188-1-yu-cheng.yu@intel.com> <20210127212524.10188-25-yu-cheng.yu@intel.com> <761ae8ce-0560-24cc-e6f7-684475cb3708@intel.com> Message-ID: <6720b1a9-f785-dbbd-1f0e-8c9090be2069@intel.com> Date: Wed, 3 Feb 2021 13:54:40 -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: <761ae8ce-0560-24cc-e6f7-684475cb3708@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 10:56 AM, Yu, Yu-cheng wrote: > On 1/29/2021 9:07 AM, Dave Hansen wrote: >> On 1/27/21 1:25 PM, Yu-cheng Yu wrote: >>> arch_prctl(ARCH_X86_CET_STATUS, u64 *args) >>> =C2=A0=C2=A0=C2=A0=C2=A0 Get CET feature status. >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0 The parameter 'args' is a pointer to a user = buffer.=C2=A0 The kernel=20 >>> returns >>> =C2=A0=C2=A0=C2=A0=C2=A0 the following information: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0 *args =3D shadow stack/IBT status >>> =C2=A0=C2=A0=C2=A0=C2=A0 *(args + 1) =3D shadow stack base address >>> =C2=A0=C2=A0=C2=A0=C2=A0 *(args + 2) =3D shadow stack size [...] >>> +int prctl_cet(int option, u64 arg2) >>> +{ >>> +=C2=A0=C2=A0=C2=A0 struct cet_status *cet; >>> +=C2=A0=C2=A0=C2=A0 unsigned int features; >>> + >>> +=C2=A0=C2=A0=C2=A0 /* >>> +=C2=A0=C2=A0=C2=A0=C2=A0 * GLIBC's ENOTSUPP =3D=3D EOPNOTSUPP =3D=3D= 95, and it does not recognize >>> +=C2=A0=C2=A0=C2=A0=C2=A0 * the kernel's ENOTSUPP (524).=C2=A0 So ret= urn EOPNOTSUPP here. >>> +=C2=A0=C2=A0=C2=A0=C2=A0 */ >>> +=C2=A0=C2=A0=C2=A0 if (!IS_ENABLED(CONFIG_X86_CET)) >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -EOPNOTSUPP; >> >> Let's ignore glibc for a moment.=C2=A0 What error code *should* the ke= rnel be >> returning here?=C2=A0 errno(3) says: >> >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 EOPNOTSUPP=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 Operation not supported on socket (POSIX.1) >> ... >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ENOTSUP=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 Operation not supported (POSIX.1) >> >=20 > Yeah, other places in kernel use ENOTSUPP.=C2=A0 This seems to be out o= f=20 > line.=C2=A0 And since the issue is long-existing, applications already = know=20 > how to deal with it.=C2=A0 I should have made that argument.=C2=A0 Chan= ge it to=20 > ENOTSUPP. When I make the change, checkpatch says... WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP #128: FILE: arch/x86/kernel/cet_prctl.c:33: + return -ENOTSUPP; Do we want to reconsider? [...]