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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 83E03C433E0 for ; Fri, 15 May 2020 22:44:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4532E206D4 for ; Fri, 15 May 2020 22:44:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4532E206D4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C23768E0003; Fri, 15 May 2020 18:44:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BD4E18E0001; Fri, 15 May 2020 18:44:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AC3858E0003; Fri, 15 May 2020 18:44:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0248.hostedemail.com [216.40.44.248]) by kanga.kvack.org (Postfix) with ESMTP id 9487E8E0001 for ; Fri, 15 May 2020 18:44:04 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 5AD848248047 for ; Fri, 15 May 2020 22:44:04 +0000 (UTC) X-FDA: 76820432808.25.bone87_5d93a1de20434 X-HE-Tag: bone87_5d93a1de20434 X-Filterd-Recvd-Size: 10513 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Fri, 15 May 2020 22:44:02 +0000 (UTC) IronPort-SDR: /jCuug+MGGaoX+a53iE+QSS/q+vfN+ky4z/y+RgpEDT3p4sIX4HwnMceL1IwajmnyNR8SziR8y 0vpUl+sEmtGA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 May 2020 15:44:01 -0700 IronPort-SDR: k1eo7I4l0vpxx5b6MH7J+XONkOgXWkDpFd5cZ7+ZI86Nz/9cWjJqvrGB0H4SbMVbxZbRO8uHTR fyoHHgokSp5A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,396,1583222400"; d="scan'208";a="266750686" Received: from thirum3x-mobl3.gar.corp.intel.com (HELO [10.255.0.216]) ([10.255.0.216]) by orsmga006.jf.intel.com with ESMTP; 15 May 2020 15:43:58 -0700 Subject: Re: [PATCH v10 01/26] Documentation/x86: Add CET description 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 References: <20200429220732.31602-1-yu-cheng.yu@intel.com> <20200429220732.31602-2-yu-cheng.yu@intel.com> <5cc163ff9058d1b27778e5f0a016c88a3b1a1598.camel@intel.com> <44c055342bda4fb4730703f987ae35195d1d0c38.camel@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: <32235ffc-6e6c-fb3d-80c4-a0478e2d0e0f@intel.com> Date: Fri, 15 May 2020 15:43:56 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <44c055342bda4fb4730703f987ae35195d1d0c38.camel@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/15/20 2:33 PM, Yu-cheng Yu wrote: > On Fri, 2020-05-15 at 11:39 -0700, Dave Hansen wrote: >> On 5/12/20 4:20 PM, Yu-cheng Yu wrote: >> Can a binary compiled with CET run without CET? >=20 > Yes, but a few details: >=20 > - The shadow stack is transparent to the application. A CET applicatio= n does > not have anything different from a non-CET application. However, if a = CET > application uses any CET instructions (e.g. INCSSP), it must first chec= k if CET > is turned on. > - If an application is compiled for IBT, the compiler inserts ENDBRs at= branch > targets. These are nops if IBT is not on. I appreciate the detailed response, but it wasn't quite what I was asking. Let's ignore IBT for now and just talk about shadow stacks. An app compiled with the new ELF flags and running on a CET-enabled kernel and CPU will start off with shadow stacks allocated and enabled, right? It can turn its shadow stack off per-thread with the new prctl. But, otherwise, it's stuck, the only way to turn shadow stacks off at startup would be editing the binary. Basically, if there ends up being a bug in an app that violates the shadow stack rules, the app is broken, period. The only recourse is to have the kernel disable CET and reboot. Is that right? >> Can a binary compiled without CET run CET-enabled code? >=20 > Partially yes, but in reality somewhat difficult. ... > - If a not-CET application does fork(), and the child wants to turn on = CET, it > would be difficult to manage the stack frames, unless the child knows w= hat is is > doing. =20 It might be hard to do, but it is possible with the patches you posted? I think you're saying that the CET-enabled binary would do arch_setup_elf_property() when it was first exec()'d. Later, it could use the new prctl(ARCH_X86_CET_DISABLE) to disable its shadow stack, then fork() and the child would not be using CET. Right? What is ARCH_X86_CET_DISABLE used for, anyway? > The JIT examples I mentioned previously run with CET enabled from the > beginning. Do you have a reason to do this? In other words, if the JI= T code > needs CET, the app could have started with CET in the first place. Let's say I have a JIT'd sandbox. I want the sandbox to be CET-protected, but the JIT engine itself not to be. > - If you are asking about dlopen(), the library will have the same sett= ing as > the main application. Do you have any reason to have a library running= with > CET, but the application does not have CET? Sure, using old binaries. That's why IBT has a legacy bitmap and things like MPX had ways of jumping into old non-enabled binaries. >> Can different threads in a process have different CET enabling state? >=20 > Yes, if the parent starts with CET, children can turn it off. How would that work, though? clone() by default will copy the parent xsave state, which means it will be CET-enabled, which means it needs a shadow stack. So, if I want a CET-free child thread, I need to clone(), then turn CET off, then free the shadow stack? >> Does this *code* work? Could you please indicate which JITs have been >> enabled to use the code in this series? How much of the new ABI is in= use? >=20 > JIT does not necessarily use all of the ABI. The JIT changes mainly fi= x stack > frames and insert ENDBRs. I do not work on JIT. What I found is LLVM = JIT fixes > are tested and in the master branch. Sljit fixes are in the release. Huh, so who is using the new prctl() ABIs? >> Where are the selftests/ for this new ABI? Were you planning on >> submitting any with this series? >=20 > The ABI is more related to the application side, and therefore most sui= table for > GLIBC unit tests. I was mostly concerned with the kernel selftests. The things in tools/testing/selftests/x86 in the kernel tree. > The more complicated areas such as pthreads, signals, ucontext, > fork() are all included there. I have been constantly running these=20 > tests without any problems. I can provide more details if testing is > the concern. For something this complicated, with new kernel ABIs, we need an in-kernel sefltest. MPX was not that much different from this feature. It required a boatload of compiler and linker changes to function. Yet, there was a simple in-kernel test for it that didn't require *any* of that big pile of toolchain bits. Is there a reason we don't have one of those for CET?