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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A8731C433EF for ; Thu, 16 Dec 2021 16:12:17 +0000 (UTC) Received: from localhost ([::1]:56818 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mxtMe-0002lb-LQ for qemu-devel@archiver.kernel.org; Thu, 16 Dec 2021 11:12:16 -0500 Received: from eggs.gnu.org ([209.51.188.92]:53656) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mxtKs-0001ai-Dq for qemu-devel@nongnu.org; Thu, 16 Dec 2021 11:10:29 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:25591) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mxtKq-0007nw-8k for qemu-devel@nongnu.org; Thu, 16 Dec 2021 11:10:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639671023; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QQ+iqxfUMXdEig3ahub5vftsIjBoaaS88sTXr8U7Ge8=; b=Nh1BpgD/WM9CztL4OkRW10syd3WzvlqTiyp18El29JfnF/WAEy9qayeyLt9urfvRIcjY8N kLchpiWCD61JKeXRWabA11oWiw30H+/eFTrjgizKACTFthjLrILJWkbkIoeM1B3nzot0K+ YcCZxKSkqfhbLPW8IryyJS07FmVxzLs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-345-Wgb11_PnPXeqD-88bdKSBQ-1; Thu, 16 Dec 2021 11:10:10 -0500 X-MC-Unique: Wgb11_PnPXeqD-88bdKSBQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 46045185302A; Thu, 16 Dec 2021 16:10:08 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.185]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 33FB35ED4E; Thu, 16 Dec 2021 16:09:51 +0000 (UTC) Date: Thu, 16 Dec 2021 16:09:49 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Dov Murik Subject: Re: [PATCH] docs: Add measurement calculation details to amd-memory-encryption.txt Message-ID: References: <20211214135910.2732101-1-dovmurik@linux.ibm.com> <336cbad3-06da-f11c-8cd1-ca058dd9c6b0@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: <336cbad3-06da-f11c-8cd1-ca058dd9c6b0@linux.ibm.com> User-Agent: Mutt/2.1.3 (2021-09-10) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.718, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Tom Lendacky , Ashish Kalra , Brijesh Singh , James Bottomley , Marcelo Tosatti , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Tobin Feldman-Fitzthum , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Dec 16, 2021 at 12:38:34PM +0200, Dov Murik wrote: > > > On 14/12/2021 20:39, Daniel P. Berrangé wrote: > > On Tue, Dec 14, 2021 at 01:59:10PM +0000, Dov Murik wrote: > >> Add a section explaining how the Guest Owner should calculate the > >> expected guest launch measurement for SEV and SEV-ES. > >> > >> Also update the name and link to the SEV API Spec document. > >> > >> Signed-off-by: Dov Murik > >> Suggested-by: Daniel P. Berrangé > >> --- > >> docs/amd-memory-encryption.txt | 50 +++++++++++++++++++++++++++++++--- > >> 1 file changed, 46 insertions(+), 4 deletions(-) > >> > >> diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt > >> index ffca382b5f..f97727482f 100644 > >> --- a/docs/amd-memory-encryption.txt > >> +++ b/docs/amd-memory-encryption.txt > >> @@ -43,7 +43,7 @@ The guest policy is passed as plaintext. A hypervisor may choose to read it, > >> but should not modify it (any modification of the policy bits will result > >> in bad measurement). The guest policy is a 4-byte data structure containing > >> several flags that restricts what can be done on a running SEV guest. > >> -See KM Spec section 3 and 6.2 for more details. > >> +See SEV API Spec [1] section 3 and 6.2 for more details. > >> > >> The guest policy can be provided via the 'policy' property (see below) > >> > >> @@ -88,7 +88,7 @@ expects. > >> LAUNCH_FINISH finalizes the guest launch and destroys the cryptographic > >> context. > >> > >> -See SEV KM API Spec [1] 'Launching a guest' usage flow (Appendix A) for the > >> +See SEV API Spec [1] 'Launching a guest' usage flow (Appendix A) for the > >> complete flow chart. > >> > >> To launch a SEV guest > >> @@ -113,6 +113,45 @@ a SEV-ES guest: > >> - Requires in-kernel irqchip - the burden is placed on the hypervisor to > >> manage booting APs. > >> > >> +Calculating expected guest launch measurement > >> +--------------------------------------------- > >> +In order to verify the guest launch measurement, The Guest Owner must compute > >> +it in the exact same way as it is calculated by the AMD-SP. SEV API Spec [1] > >> +section 6.5.1 describes the AMD-SP operations: > >> + > >> + GCTX.LD is finalized, producing the hash digest of all plaintext data > >> + imported into the guest. > >> + > >> + The launch measurement is calculated as: > >> + > >> + HMAC(0x04 || API_MAJOR || API_MINOR || BUILD || GCTX.POLICY || GCTX.LD || MNONCE; GCTX.TIK) > >> + > >> + where "||" represents concatenation. > >> + > >> +The values of API_MAJOR, API_MINOR, BUILD, and GCTX.POLICY can be obtained > >> +from the 'query-sev' qmp command. > >> + > >> +The value of MNONCE is part of the response of 'query-sev-launch-measure': it > >> +is the last 16 bytes of the base64-decoded data field (see SEV API Spec [1] > >> +section 6.5.2 Table 52: LAUNCH_MEASURE Measurement Buffer). > >> + > >> +The value of GCTX.LD is SHA256(firmware_blob || kernel_hashes_blob || vmsas_blob), > >> +where: > >> + > >> +* firmware_blob is the content of the entire firmware flash file (for example, > >> + OVMF.fd). > > > > Lets add a caveat that the firmware flash should be built to be stateless > > ie that it is not secure to attempt to measure a guest where the firmware > > uses an NVRAM store. > > > > * firmware_blob is the content of the entire firmware flash file (for > example, OVMF.fd). Note that you must build a stateless firmware file > which doesn't use an NVRAM store, because the NVRAM area is not > measured, and therefore it is not secure to use a firmware which uses > state from an NVRAM store. Looks good to me. > >> +* if kernel is used, and kernel-hashes=on, then kernel_hashes_blob is the > >> + content of PaddedSevHashTable (including the zero padding), which itself > >> + includes the hashes of kernel, initrd, and cmdline that are passed to the > >> + guest. The PaddedSevHashTable struct is defined in target/i386/sev.c . > >> +* if SEV-ES is enabled (policy & 0x4 != 0), vmsas_blob is the concatenation of > >> + all VMSAs of the guest vcpus. Each VMSA is 4096 bytes long; its content is > >> + defined inside Linux kernel code as struct vmcb_save_area, or in AMD APM > >> + Volume 2 [2] Table B-2: VMCB Layout, State Save Area. > > > > Is there any practical guidance we can give apps on the way the VMSAs > > can be expected to be initialized ? eg can they assume essentially > > all fields in vmcb_save_area are 0 initialized except for certain > > ones ? Is initialization likely to vary at all across KVM or EDK2 > > vesions or something ? > > From my own experience, the VMSA of vcpu0 doesn't change; it is basically what QEMU > sets up in x86_cpu_reset() (which is mostly zeros but not all). I don't know if it > may change in newer QEMU (machine types?) or kvm. As for vcpu1+, in SEV-ES the > CS:EIP for the APs is taken from a GUIDed table at the end of the OVMF image, and has > actually changed a few months ago when the memory layout changed to support both TDX > and SEV. That is an unplesantly large number of moving parts that could potentially impact the expected state :-( I think we need to be careful to avoid gratuitous changes, to avoid creating a combinatorial expansion in the number of possibly valid VMSA blocks. It makes me wonder if we need to think about defining some standard approach for distro vendors (and/or cloud vendors) to publish the expected contents for various combinations of their software pieces. > > > Here are the VMSAs for my 2-vcpu SEV-ES VM: > > > $ hd vmsa/vmsa_cpu0.bin ...snipp... was there a nice approach / tool you used to capture this initial state ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|