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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 4DCC5C2BBDB for ; Thu, 3 Sep 2020 02:54:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 342AA20758 for ; Thu, 3 Sep 2020 02:54:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728160AbgICCyB (ORCPT ); Wed, 2 Sep 2020 22:54:01 -0400 Received: from mga09.intel.com ([134.134.136.24]:36512 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726177AbgICCx6 (ORCPT ); Wed, 2 Sep 2020 22:53:58 -0400 IronPort-SDR: XQWA3DQBk98GF3ACSAadTWXp96zAAP1DM3NGiJ+wP1rBH/UzP9MqlRCd3twdGLT0ljniCtJJJ3 mE9qblWcfo1A== X-IronPort-AV: E=McAfee;i="6000,8403,9732"; a="158496325" X-IronPort-AV: E=Sophos;i="5.76,384,1592895600"; d="scan'208";a="158496325" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Sep 2020 19:53:58 -0700 IronPort-SDR: kuo7JgczJbT83sHrpVfgqJG/Jqc0ewkrsV3LhjRM7Af8/qwMoGAWfgBC17ng+934Hve0sPN83A 64xElWOhzhng== X-IronPort-AV: E=Sophos;i="5.76,384,1592895600"; d="scan'208";a="446740813" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.147.104]) ([10.209.147.104]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Sep 2020 19:53:56 -0700 Subject: Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET To: Jann Horn Cc: the arch/x86 maintainers , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , 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 References: <20200825002645.3658-1-yu-cheng.yu@intel.com> <20200825002645.3658-7-yu-cheng.yu@intel.com> <9be5356c-ec51-4541-89e5-05a1727a09a8@intel.com> From: "Yu, Yu-cheng" Message-ID: <1d00a4ed-6f2e-bafd-3540-292e31f1685b@intel.com> Date: Wed, 2 Sep 2020 19:53:55 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/2/2020 5:33 PM, Jann Horn wrote: > On Thu, Sep 3, 2020 at 12:13 AM Yu, Yu-cheng wrote: >> On 9/2/2020 1:03 PM, Jann Horn wrote: >>> On Tue, Aug 25, 2020 at 2:30 AM Yu-cheng Yu wrote: >>>> Add REGSET_CET64/REGSET_CET32 to get/set CET MSRs: >>>> >>>> IA32_U_CET (user-mode CET settings) and >>>> IA32_PL3_SSP (user-mode Shadow Stack) >>> [...] >>>> diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c >>> [...] >>>> +int cetregs_get(struct task_struct *target, const struct user_regset *regset, >>>> + struct membuf to) >>>> +{ >>>> + struct fpu *fpu = &target->thread.fpu; >>>> + struct cet_user_state *cetregs; >>>> + >>>> + if (!boot_cpu_has(X86_FEATURE_SHSTK)) >>>> + return -ENODEV; >>>> + >>>> + fpu__prepare_read(fpu); >>>> + cetregs = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER); >>>> + if (!cetregs) >>>> + return -EFAULT; >>> >>> Can this branch ever be hit without a kernel bug? If yes, I think >>> -EFAULT is probably a weird error code to choose here. If no, this >>> should probably use WARN_ON(). Same thing in cetregs_set(). >>> >> >> When a thread is not CET-enabled, its CET state does not exist. I >> looked at EFAULT, and it means "Bad address". Maybe this can be ENODEV, >> which means "No such device"? > > Yeah, I guess ENODEV might fit reasonably well. > I will update it. Thanks!