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 47C80C433DB for ; Fri, 29 Jan 2021 17:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14B6F64D92 for ; Fri, 29 Jan 2021 17:09:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232147AbhA2RI5 (ORCPT ); Fri, 29 Jan 2021 12:08:57 -0500 Received: from mga07.intel.com ([134.134.136.100]:22339 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229661AbhA2RHq (ORCPT ); Fri, 29 Jan 2021 12:07:46 -0500 IronPort-SDR: p8Wk3Hi2WuNznyoMrufDgJFn7F9VOXeBmA4l4QoM+/O1YkE4hafl3i0YrK5VktZ0X0WnCGBb98 eum5jgSYygUw== X-IronPort-AV: E=McAfee;i="6000,8403,9879"; a="244539471" X-IronPort-AV: E=Sophos;i="5.79,386,1602572400"; d="scan'208";a="244539471" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jan 2021 09:07:04 -0800 IronPort-SDR: C/Gip6dt70g3XPeD/k4QNm3XwpXa4g6YixqTOPTrUIQe2OCJdT+eg0GeWv9j/C1xQYmir9cCxf nxlk7ED7pvqw== X-IronPort-AV: E=Sophos;i="5.79,386,1602572400"; d="scan'208";a="576531508" Received: from bkmossma-mobl.amr.corp.intel.com (HELO [10.209.175.74]) ([10.209.175.74]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jan 2021 09:07:02 -0800 Subject: Re: [PATCH v18 24/25] x86/cet/shstk: Add arch_prctl functions for shadow stack To: Yu-cheng Yu , 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> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzShEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gPGRhdmVAc3I3MS5uZXQ+wsF7BBMBAgAlAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAUCTo3k0QIZAQAKCRBoNZUwcMmSsMO2D/421Xg8pimb9mPzM5N7khT0 2MCnaGssU1T59YPE25kYdx2HntwdO0JA27Wn9xx5zYijOe6B21ufrvsyv42auCO85+oFJWfE K2R/IpLle09GDx5tcEmMAHX6KSxpHmGuJmUPibHVbfep2aCh9lKaDqQR07gXXWK5/yU1Dx0r VVFRaHTasp9fZ9AmY4K9/BSA3VkQ8v3OrxNty3OdsrmTTzO91YszpdbjjEFZK53zXy6tUD2d e1i0kBBS6NLAAsqEtneplz88T/v7MpLmpY30N9gQU3QyRC50jJ7LU9RazMjUQY1WohVsR56d ORqFxS8ChhyJs7BI34vQusYHDTp6PnZHUppb9WIzjeWlC7Jc8lSBDlEWodmqQQgp5+6AfhTD kDv1a+W5+ncq+Uo63WHRiCPuyt4di4/0zo28RVcjtzlGBZtmz2EIC3vUfmoZbO/Gn6EKbYAn rzz3iU/JWV8DwQ+sZSGu0HmvYMt6t5SmqWQo/hyHtA7uF5Wxtu1lCgolSQw4t49ZuOyOnQi5 f8R3nE7lpVCSF1TT+h8kMvFPv3VG7KunyjHr3sEptYxQs4VRxqeirSuyBv1TyxT+LdTm6j4a mulOWf+YtFRAgIYyyN5YOepDEBv4LUM8Tz98lZiNMlFyRMNrsLV6Pv6SxhrMxbT6TNVS5D+6 UorTLotDZKp5+M7BTQRUY85qARAAsgMW71BIXRgxjYNCYQ3Xs8k3TfAvQRbHccky50h99TUY sqdULbsb3KhmY29raw1bgmyM0a4DGS1YKN7qazCDsdQlxIJp9t2YYdBKXVRzPCCsfWe1dK/q 66UVhRPP8EGZ4CmFYuPTxqGY+dGRInxCeap/xzbKdvmPm01Iw3YFjAE4PQ4hTMr/H76KoDbD cq62U50oKC83ca/PRRh2QqEqACvIH4BR7jueAZSPEDnzwxvVgzyeuhwqHY05QRK/wsKuhq7s UuYtmN92Fasbxbw2tbVLZfoidklikvZAmotg0dwcFTjSRGEg0Gr3p/xBzJWNavFZZ95Rj7Et db0lCt0HDSY5q4GMR+SrFbH+jzUY/ZqfGdZCBqo0cdPPp58krVgtIGR+ja2Mkva6ah94/oQN lnCOw3udS+Eb/aRcM6detZr7XOngvxsWolBrhwTQFT9D2NH6ryAuvKd6yyAFt3/e7r+HHtkU kOy27D7IpjngqP+b4EumELI/NxPgIqT69PQmo9IZaI/oRaKorYnDaZrMXViqDrFdD37XELwQ gmLoSm2VfbOYY7fap/AhPOgOYOSqg3/Nxcapv71yoBzRRxOc4FxmZ65mn+q3rEM27yRztBW9 AnCKIc66T2i92HqXCw6AgoBJRjBkI3QnEkPgohQkZdAb8o9WGVKpfmZKbYBo4pEAEQEAAcLB XwQYAQIACQUCVGPOagIbDAAKCRBoNZUwcMmSsJeCEACCh7P/aaOLKWQxcnw47p4phIVR6pVL e4IEdR7Jf7ZL00s3vKSNT+nRqdl1ugJx9Ymsp8kXKMk9GSfmZpuMQB9c6io1qZc6nW/3TtvK pNGz7KPPtaDzvKA4S5tfrWPnDr7n15AU5vsIZvgMjU42gkbemkjJwP0B1RkifIK60yQqAAlT YZ14P0dIPdIPIlfEPiAWcg5BtLQU4Wg3cNQdpWrCJ1E3m/RIlXy/2Y3YOVVohfSy+4kvvYU3 lXUdPb04UPw4VWwjcVZPg7cgR7Izion61bGHqVqURgSALt2yvHl7cr68NYoFkzbNsGsye9ft M9ozM23JSgMkRylPSXTeh5JIK9pz2+etco3AfLCKtaRVysjvpysukmWMTrx8QnI5Nn5MOlJj 1Ov4/50JY9pXzgIDVSrgy6LYSMc4vKZ3QfCY7ipLRORyalFDF3j5AGCMRENJjHPD6O7bl3Xo 4DzMID+8eucbXxKiNEbs21IqBZbbKdY1GkcEGTE7AnkA3Y6YB7I/j9mQ3hCgm5muJuhM/2Fr OPsw5tV/LmQ5GXH0JQ/TZXWygyRFyyI2FqNTx4WHqUn3yFj8rwTAU1tluRUYyeLy0ayUlKBH ybj0N71vWO936MqP6haFERzuPAIpxj2ezwu0xb1GjTk4ynna6h5GjnKgdfOWoRtoWndMZxbA z5cecg== Message-ID: Date: Fri, 29 Jan 2021 09:07:01 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210127212524.10188-25-yu-cheng.yu@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 What's the deal for 32-bit binaries? The in-kernel code looks 64-bit only, but I don't see anything restricting the interface to 64-bit. > +static int copy_status_to_user(struct cet_status *cet, u64 arg2) This has static scope, but it's still awfully generically named. A cet_ prefix would be nice. > +{ > + u64 buf[3] = {0, 0, 0}; > + > + if (cet->shstk_size) { > + buf[0] |= GNU_PROPERTY_X86_FEATURE_1_SHSTK; > + buf[1] = (u64)cet->shstk_base; > + buf[2] = (u64)cet->shstk_size; What's the casting for? > + } > + > + return copy_to_user((u64 __user *)arg2, buf, sizeof(buf)); > +} > + > +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) > + cet = ¤t->thread.cet; > + > + if (option == ARCH_X86_CET_STATUS) > + return copy_status_to_user(cet, arg2); What's the point of doing copy_status_to_user() if the processor doesn't support CET? In other words, shouldn't this be below the CPU feature check? Also, please cast arg2 *here*. It becomes a user pointer here, not at the copy_to_user(). > + if (!static_cpu_has(X86_FEATURE_CET)) > + return -EOPNOTSUPP; So, you went to the trouble of adding a disabled-features.h entry for this. Why not just do: if (cpu_feature_enabled(X86_FEATURE_CET)) ... instead of the IS_ENABLED() check above? That should get rid of one of these if's. > + switch (option) { > + case ARCH_X86_CET_DISABLE: > + if (cet->locked) > + return -EPERM; > + > + features = (unsigned int)arg2; What's the purpose of this cast? > + if (features & ~GNU_PROPERTY_X86_FEATURE_1_VALID) > + return -EINVAL; > + if (features & GNU_PROPERTY_X86_FEATURE_1_SHSTK) > + cet_disable_shstk(); > + return 0; This doesn't enforce that the high bits of arg2 be 0. Shouldn't we call them reserved and enforce that they be 0? > + case ARCH_X86_CET_LOCK: > + cet->locked = 1; > + return 0; This needs to check for and enforce that arg2==0. > + default: > + return -ENOSYS; > + } > +}