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David Alan Gilbert" , Tom Lendacky , Paolo Bonzini , Dov Murik , David Gibson , kvm@vger.kernel.org, Michael Roth , Eduardo Habkost Subject: Re: [RFC PATCH 2/6] i386/sev: extend sev-guest property to include SEV-SNP To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20210709215550.32496-1-brijesh.singh@amd.com> <20210709215550.32496-3-brijesh.singh@amd.com> From: Brijesh Singh Message-ID: <34b975c7-6d14-733a-79a5-2eb1efff7538@amd.com> Date: Tue, 13 Jul 2021 08:54:44 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SN4PR0801CA0002.namprd08.prod.outlook.com (2603:10b6:803:29::12) To SN6PR12MB2718.namprd12.prod.outlook.com (2603:10b6:805:6f::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.236.31.95] (165.204.77.1) by SN4PR0801CA0002.namprd08.prod.outlook.com (2603:10b6:803:29::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4331.21 via Frontend Transport; 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envelope-from=brijesh.singh@amd.com; helo=NAM12-BN8-obe.outbound.protection.outlook.com X-Spam_score_int: -5 X-Spam_score: -0.6 X-Spam_bar: / X-Spam_report: (-0.6 / 5.0 requ) DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.368, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/12/21 11:24 AM, Daniel P. Berrangé wrote:>> >> policy: 8 bytes >> flags: 8 bytes >> id_block: 96 bytes >> id_auth: 4096 bytes >> host_data: 32 bytes >> gosvw: 16 bytes > > Only the id_auth parameter is really considered large here. > > When you say "up to a page size", that implies that the size is > actually variable. Is that correct, and if so, what is a real > world common size going to be ? Is the common size much smaller > than this upper limit ? If so I'd just ignore the issue entirely. Looking at the recent spec, it appears that id_auth is fixed to 4K. > > If not, then, 4k on the command line is certainly ugly, but isn't > technically impossible. It would be similarly ugly to have this > value stuffed into a libvirt XML configuration for that matter. > > One option is to supply only that one parameter via an external > file, with the file being an opaque blob whose context is the > parameter value thus avoiding inventing a custom file format > parser. > > When "id_auth" is described as "authentication data", are there > any secrecy requirements around this ? > Yes this sounds much better, we have been using the similar approach for the SEV in which we pass the PDH and session blob through the file. > QEMU does have the '-object secret' framework for passing blobs > of sensitive data to QEMU and can allow passing via a file: > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fqemu-project.gitlab.io%2Fqemu%2Fsystem%2Fsecrets.html&data=04%7C01%7Cbrijesh.singh%40amd.com%7C891fdc1ab0d8483aecb808d945519054%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637617038899405482%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=8AHUC3DeyauxT4Pd2ZkUJkDyu9XHtexybM0BgdRlego%3D&reserved=0 > > Even if this doesn't actually need to be kept private, we > could decide to simply (ab)use the 'secret' object anyway > as a way to let it be passed in out of band via a file. > The content of the field does not need to be protected. It's a public information, so I am not sure the secrets object fits here. thanks