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=-7.9 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 8F4B4C433E9 for ; Thu, 3 Sep 2020 16:21:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 76AFF20829 for ; Thu, 3 Sep 2020 16:21:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728337AbgICQVT (ORCPT ); Thu, 3 Sep 2020 12:21:19 -0400 Received: from mga02.intel.com ([134.134.136.20]:3943 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726292AbgICQVR (ORCPT ); Thu, 3 Sep 2020 12:21:17 -0400 IronPort-SDR: SBu/OVMwEM4iqnI+P+Z0V5LKrshiHqNKrOA6f07eDzqW9DMm2LlRL+0fKRLJjsGWWS4S/fswi/ 4XwYE9x7PqGQ== X-IronPort-AV: E=McAfee;i="6000,8403,9733"; a="145348301" X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="145348301" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 09:21:15 -0700 IronPort-SDR: +Pe0zUpW7n8ydj/YOVTaKR79uc3vTuh90uRyD5Hw3BPUUqT/NnJucVFtliTUbdOkPMAUiK4O9f Kyp5qF3qstzg== X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="503120164" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.173.133]) ([10.209.173.133]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 09:21:11 -0700 Subject: Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET To: Dave Hansen , Andy Lutomirski Cc: Jann Horn , 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: <46e42e5e-0bca-5f3f-efc9-5ab15827cc0b@intel.com> <40BC093A-F430-4DCC-8DC0-2BA90A6FC3FA@amacapital.net> <88261152-2de1-fe8d-7ab0-acb108e97e04@intel.com> <1b51d89c-c7de-2032-df23-e138d1369ffa@intel.com> From: "Yu, Yu-cheng" Message-ID: <3967f126-f7ea-36fd-bec0-dfbbc46ef221@intel.com> Date: Thu, 3 Sep 2020 09:21:10 -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: <1b51d89c-c7de-2032-df23-e138d1369ffa@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 9/3/2020 9:11 AM, Dave Hansen wrote: > On 9/3/20 9:09 AM, Yu, Yu-cheng wrote: >> If the debugger is going to write an MSR, only in the third case would >> this make a slight sense.  For example, if the system has CET enabled, >> but the task does not have CET enabled, and GDB is writing to a CET MSR. >>  But still, this is strange to me. > > If this is strange, then why do we even _implement_ writes? > For example, if the task has CET enabled, and it is in a control protection fault, the debugger can clear the task's IBT state, or unwind the shadow stack, etc. But if the task does not have CET enabled (its CET MSRs are in INIT state), it would make sense for the PTRACE call to return failure than doing something else, right?