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 2CC54C433E6 for ; Wed, 3 Feb 2021 21:55:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E696A64E46 for ; Wed, 3 Feb 2021 21:55:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231732AbhBCVz3 (ORCPT ); Wed, 3 Feb 2021 16:55:29 -0500 Received: from mga12.intel.com ([192.55.52.136]:31742 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229959AbhBCVzY (ORCPT ); Wed, 3 Feb 2021 16:55:24 -0500 IronPort-SDR: dki/tcFY5jf6CsHBIUnCVpY1HYgNYNp7jLC4VREjng0wiB6+y/PkPMlAN8Aoue6jLUExiL9HMm Py7zDnXbcHRg== X-IronPort-AV: E=McAfee;i="6000,8403,9884"; a="160290204" X-IronPort-AV: E=Sophos;i="5.79,399,1602572400"; d="scan'208";a="160290204" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.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: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) >>>      Get CET feature status. >>> >>>      The parameter 'args' is a pointer to a user buffer.  The kernel >>> returns >>>      the following information: >>> >>>      *args = shadow stack/IBT status >>>      *(args + 1) = shadow stack base address >>>      *(args + 2) = shadow stack size [...] >>> +int prctl_cet(int option, u64 arg2) >>> +{ >>> +    struct cet_status *cet; >>> +    unsigned int features; >>> + >>> +    /* >>> +     * GLIBC's ENOTSUPP == EOPNOTSUPP == 95, and it does not recognize >>> +     * the kernel's ENOTSUPP (524).  So return EOPNOTSUPP here. >>> +     */ >>> +    if (!IS_ENABLED(CONFIG_X86_CET)) >>> +        return -EOPNOTSUPP; >> >> Let's ignore glibc for a moment.  What error code *should* the kernel be >> returning here?  errno(3) says: >> >>         EOPNOTSUPP      Operation not supported on socket (POSIX.1) >> ... >>         ENOTSUP         Operation not supported (POSIX.1) >> > > Yeah, other places in kernel use ENOTSUPP.  This seems to be out of > line.  And since the issue is long-existing, applications already know > how to deal with it.  I should have made that argument.  Change it to > 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? [...]