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 DD75CC43460 for ; Tue, 18 May 2021 18:05:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE0D4611BF for ; Tue, 18 May 2021 18:05:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351454AbhERSG5 (ORCPT ); Tue, 18 May 2021 14:06:57 -0400 Received: from mga01.intel.com ([192.55.52.88]:26931 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346758AbhERSGz (ORCPT ); Tue, 18 May 2021 14:06:55 -0400 IronPort-SDR: q+McRJhdftoHISkLhODa1E5JP+ke3SD4bEIeuLAwCAfubEZrATPlunM/k0+DtU5DNUZ+7KsKkI RRVnQKeSedzA== X-IronPort-AV: E=McAfee;i="6200,9189,9988"; a="221838914" X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="221838914" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2021 11:05:30 -0700 IronPort-SDR: gAUNy8H1tWzyDtk3RjWGu7NYwEdtvHR844tMogSjaHv7ceZTTVu4XZLZKd+4fKBQaVCefCmmE4 wSoG94ONbg3g== X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="473078661" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.166.158]) ([10.209.166.158]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2021 11:05:28 -0700 Subject: Re: [PATCH v26 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines To: Eugene Syromiatnikov Cc: Borislav Petkov , 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 , Cyrill Gorcunov , Dave Hansen , 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 , Haitao Huang References: <20210427204315.24153-1-yu-cheng.yu@intel.com> <20210427204315.24153-25-yu-cheng.yu@intel.com> <20210518001316.GR15897@asgard.redhat.com> From: "Yu, Yu-cheng" Message-ID: Date: Tue, 18 May 2021 11:05:25 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210518001316.GR15897@asgard.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/17/2021 5:14 PM, Eugene Syromiatnikov wrote: > On Mon, May 17, 2021 at 01:55:01PM -0700, Yu, Yu-cheng wrote: >> On 5/17/2021 12:45 AM, Borislav Petkov wrote: >>> On Tue, Apr 27, 2021 at 01:43:09PM -0700, Yu-cheng Yu wrote: >>>> +static inline int write_user_shstk_32(u32 __user *addr, u32 val) >>>> +{ >>>> + WARN_ONCE(1, "%s used but not supported.\n", __func__); >>>> + return -EFAULT; >>>> +} >>>> +#endif >>> >>> What is that supposed to catch? Any concrete (mis-)use cases? >>> >> >> If 32-bit apps are not supported, there should be no need of 32-bit shadow >> stack write, otherwise there is a bug. > > Speaking of which, I wonder what would happen if a 64-bit process makes > a 32-bit system call (using int 0x80, for example), and gets a signal. > Yes, that's right. Thanks! I should have said, if neither IA32 nor X32 is supported. Yu-cheng