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=-5.5 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 B305EC433DB for ; Wed, 10 Feb 2021 16:26:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F67A64E76 for ; Wed, 10 Feb 2021 16:26:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232100AbhBJQ0S (ORCPT ); Wed, 10 Feb 2021 11:26:18 -0500 Received: from mga14.intel.com ([192.55.52.115]:56603 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232152AbhBJQZz (ORCPT ); Wed, 10 Feb 2021 11:25:55 -0500 IronPort-SDR: IoBfMPJAhiVnMGDTtWl6YUoPwzTtjjUQERD3c2ha/LoLpCynd8C+qdtRBCrfROe003k8rGvqIy UCpPFVu/LZnQ== X-IronPort-AV: E=McAfee;i="6000,8403,9891"; a="181328877" X-IronPort-AV: E=Sophos;i="5.81,168,1610438400"; d="scan'208";a="181328877" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2021 08:25:13 -0800 IronPort-SDR: vh8ca9Rk+hpZui2u9ziCQUQP2R9XfBCgQ5uFK92I5KW/SHqkD8HCAqFw8HZ1ZShHDhWeADYWxo JBLA5mwGewUA== X-IronPort-AV: E=Sophos;i="5.81,168,1610438400"; d="scan'208";a="488795823" Received: from tryu-mobl2.amr.corp.intel.com (HELO [10.209.100.152]) ([10.209.100.152]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2021 08:25:12 -0800 Subject: Re: [PATCH 6/7] x86/boot/compressed/64: Check SEV encryption in 32-bit boot-path To: Joerg Roedel , x86@kernel.org Cc: Joerg Roedel , hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Sean Christopherson , Martin Radev , Arvind Sankar , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org References: <20210210102135.30667-1-joro@8bytes.org> <20210210102135.30667-7-joro@8bytes.org> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210210102135.30667-7-joro@8bytes.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2/10/21 2:21 AM, Joerg Roedel wrote: > +1: rdrand %eax > + jnc 1b > +2: rdrand %ebx > + jnc 2b > + > + /* Store to memory and keep it in the registers */ > + movl %eax, rva(sev_check_data)(%ebp) > + movl %ebx, rva(sev_check_data+4)(%ebp) > + > + /* Enable paging to see if encryption is active */ > + movl %cr0, %edx /* Backup %cr0 in %edx */ > + movl $(X86_CR0_PG | X86_CR0_PE), %ecx /* Enable Paging and Protected mode */ > + movl %ecx, %cr0 > + > + cmpl %eax, rva(sev_check_data)(%ebp) > + jne 3f > + cmpl %ebx, rva(sev_check_data+4)(%ebp) > + jne 3f > + > + movl %edx, %cr0 /* Restore previous %cr0 */ > + > + jmp 4f This is all very cute. But, if this fails, it means that the .data section is now garbage, right?. I guess failing here is less entertaining than trying to run the kernel with random garbage in .data, but it doesn't make it very far either way, right? Why bother with rdrand, though? Couldn't you just pick any old piece of .data and compare before and after?