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=-2.2 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 B3C45C54FD0 for ; Fri, 24 Apr 2020 22:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95F1E20767 for ; Fri, 24 Apr 2020 22:53:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726141AbgDXWxL (ORCPT ); Fri, 24 Apr 2020 18:53:11 -0400 Received: from mga11.intel.com ([192.55.52.93]:2083 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725874AbgDXWxL (ORCPT ); Fri, 24 Apr 2020 18:53:11 -0400 IronPort-SDR: f6W4JBYLu/r9zYCtrS7qAIL/zVrg/pvo6l+7Prk3m60MZoApP9PEVCbsa+ZIFG3QjWgeulIQiT VToLiyZDRMKQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Apr 2020 15:53:10 -0700 IronPort-SDR: SMTKaa/W1dwcaDZ9uCNjIskBxvIAv4RAYS02wPLr7W4WbNrkSIutDHuoegRtg8zJnPOr/NjZ10 YBhjjQt0fMUQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,313,1583222400"; d="scan'208";a="259991541" Received: from bfallaha-mobl2.amr.corp.intel.com (HELO [10.252.132.86]) ([10.252.132.86]) by orsmga006.jf.intel.com with ESMTP; 24 Apr 2020 15:53:10 -0700 Subject: Re: [PATCH] Allow RDTSC and RDTSCP from userspace To: Tom Lendacky , Mike Stunes , joro@8bytes.org Cc: dan.j.williams@intel.com, dave.hansen@linux.intel.com, hpa@zytor.com, jgross@suse.com, jroedel@suse.de, jslaby@suse.cz, keescook@chromium.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, luto@kernel.org, peterz@infradead.org, thellstrom@vmware.com, virtualization@lists.linux-foundation.org, x86@kernel.org, Sean Christopherson References: <20200319091407.1481-56-joro@8bytes.org> <20200424210316.848878-1-mstunes@vmware.com> <2c49061d-eb84-032e-8dcb-dd36a891ce90@intel.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; keydata= mQINBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC 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/aCccJK18ZwNjFhqr4MliQARAQABtEVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT6JAjgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lcuQINBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABiQIfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y Message-ID: <4d2ac222-a896-a60e-9b3c-b35aa7e81a97@intel.com> Date: Fri, 24 Apr 2020 15:53:09 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/24/20 2:27 PM, Tom Lendacky wrote: > On 4/24/20 4:24 PM, Dave Hansen wrote: >> On 4/24/20 2:03 PM, Mike Stunes wrote: >>> I needed to allow RDTSC(P) from userspace and in early boot in order to >>> get userspace started properly. Patch below. >>> >>> --- >>> SEV-ES guests will need to execute rdtsc and rdtscp from userspace and >>> during early boot. Move the rdtsc(p) #VC handler into common code and >>> extend the #VC handlers. >> >> Do SEV-ES guests _always_ #VC on rdtsc(p)? > > Only if the hypervisor is intercepting those instructions. Ahh, so any instruction that can have an instruction intercept set potentially needs to be able to tolerate a #VC? Those instruction intercepts are under the control of the (untrusted relative to the guest) hypervisor, right? >From the main sev-es series: +#ifdef CONFIG_AMD_MEM_ENCRYPT +idtentry vmm_communication do_vmm_communication has_error_code=1 +#endif Since this is set as non-paranoid, that both limits the instructions that can be used in entry paths *and* limits the future architecture from being able add instructions that a current SEV-ES guest doesn't know about. Does SEV-ES have versioning so guests can tell if they might be subject to new interrupt intercepts for which they are not prepared? I didn't see anything obvious in section 15.35 of the manual. There's also a nugget in the manual that says: > Similarly, the hypervisor should avoid setting intercept bits for > events that would occur in the #VC handler (such as IRET). That's a fun point because it means that the (untrusted) hypervisor can cause endless faults. I *guess* we have mitigation for this with our stack guard pages, but it's still a bit nasty that the hypervisor can arbitrarily land a guest in the double-fault handler. It just all seems a bit weak for the hypervisor to be considered untrusted. But, it's _certainly_ a steep in the right direction from SEV.