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=-6.9 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 EABC7C43461 for ; Tue, 8 Sep 2020 18:25:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B1642208FE for ; Tue, 8 Sep 2020 18:25:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728507AbgIHSZ2 (ORCPT ); Tue, 8 Sep 2020 14:25:28 -0400 Received: from mga04.intel.com ([192.55.52.120]:51499 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726642AbgIHSZZ (ORCPT ); Tue, 8 Sep 2020 14:25:25 -0400 IronPort-SDR: dG5By9HBXXJoXUGErJ6k/+2MyMDAkdGFigq6MHw5IC1d4AaGwY/WhuE+YiEFL0JTzYmNp+z0O0 rSqFh8q/Su1g== X-IronPort-AV: E=McAfee;i="6000,8403,9738"; a="155602347" X-IronPort-AV: E=Sophos;i="5.76,406,1592895600"; d="scan'208";a="155602347" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Sep 2020 11:25:23 -0700 IronPort-SDR: bTS1USQJwqhUAqTZ1mXCWmgKPD1f8ak2tiuGhfZUz3y/kZrFWzwSTM0whGUwwHvZRrXPondA26 9gLrCKJRf3PA== X-IronPort-AV: E=Sophos;i="5.76,406,1592895600"; d="scan'208";a="448891489" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.111.239]) ([10.209.111.239]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Sep 2020 11:25:21 -0700 Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack To: Dave Hansen , Andy Lutomirski Cc: Dave Martin , "H.J. Lu" , Florian Weimer , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , "open list:DOCUMENTATION" , Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Weijiang Yang References: <086c73d8-9b06-f074-e315-9964eb666db9@intel.com> <73c2211f-8811-2d9f-1930-1c5035e6129c@intel.com> <20200826164604.GW6642@arm.com> <87ft892vvf.fsf@oldenburg2.str.redhat.com> <0e9996bc-4c1b-cc99-9616-c721b546f857@intel.com> <4f2dfefc-b55e-bf73-f254-7d95f9c67e5c@intel.com> <20200901102758.GY6642@arm.com> <32005d57-e51a-7c7f-4e86-612c2ff067f3@intel.com> <46dffdfd-92f8-0f05-6164-945f217b0958@intel.com> From: "Yu, Yu-cheng" Message-ID: <6e1e22a5-1b7f-2783-351e-c8ed2d4893b8@intel.com> Date: Tue, 8 Sep 2020 11:25:20 -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: 8bit Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 9/8/2020 10:57 AM, Dave Hansen wrote: > On 9/8/20 10:50 AM, Yu, Yu-cheng wrote: >> What about this: >> >> - Do not add any new syscall or arch_prctl for creating a new shadow stack. >> >> - Add a new arch_prctl that can turn an anonymous mapping to a shadow >> stack mapping. >> >> This allows the application to do whatever is necessary.  It can even >> allow GDB or JIT code to create or fix a call stack. > > Fine with me. But, it's going to effectively be > > arch_prctl(PR_CONVERT_TO_SHS..., addr, len); > > when it could just as easily be: > > madvise(addr, len, MADV_SHSTK...); > > Or a new syscall. The only question in my mind is whether we want to do > something generic that we can use for other similar things in the > future, like: > > madvise2(addr, len, flags, MADV2_SHSTK...); > > I don't really feel strongly about it, though. Could you please share > your logic on why you want a prctl() as opposed to a whole new syscall? > A new syscall is more intrusive, I think. When creating a new shadow stack, the kernel also installs a restore token on the top of the new shadow stack, and it is somewhat x86-specific. So far no other arch's need this. Yes, madvise is better if the kernel only needs to change the mapping. The application itself can create the restore token before calling madvise().