Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com;
From:   Brijesh Singh <brijesh.singh@amd.com>
To:     <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
        <kvm@vger.kernel.org>, <linux-efi@vger.kernel.org>,
        <platform-driver-x86@vger.kernel.org>,
        <linux-coco@lists.linux.dev>, <linux-mm@kvack.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        "Vitaly Kuznetsov" <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        "Andy Lutomirski" <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        "Peter Zijlstra" <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        <brijesh.ksingh@gmail.com>, <tony.luck@intel.com>,
        <marcorr@google.com>, <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Liam Merwick <liam.merwick@oracle.com>
Subject: [PATCH v10 43/45] virt: sevguest: Add support to derive key
Date:   Wed, 9 Feb 2022 12:10:37 -0600
Message-ID: <20220209181039.1262882-44-brijesh.singh@amd.com>
In-Reply-To: <20220209181039.1262882-1-brijesh.singh@amd.com>
References: <20220209181039.1262882-1-brijesh.singh@amd.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Feb 2022 18:12:42.1620
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 64b4fbdc-7ffd-4dbc-6dc4-08d9ebf7c3d2
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT013.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR12MB5162
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE
	autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

The SNP_GET_DERIVED_KEY ioctl interface can be used by the SNP guest to
ask the firmware to provide a key derived from a root key. The derived
key may be used by the guest for any purposes it chooses, such as a
sealing key or communicating with the external entities.

See SEV-SNP firmware spec for more information.

Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 Documentation/virt/coco/sevguest.rst  | 17 ++++++++++
 drivers/virt/coco/sevguest/sevguest.c | 45 +++++++++++++++++++++++++++
 include/uapi/linux/sev-guest.h        | 17 ++++++++++
 3 files changed, 79 insertions(+)

diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
index 34feff6d5940..ae2e76f59435 100644
--- a/Documentation/virt/coco/sevguest.rst
+++ b/Documentation/virt/coco/sevguest.rst
@@ -77,6 +77,23 @@ On success, the snp_report_resp.data will contains the report. The report
 contain the format described in the SEV-SNP specification. See the SEV-SNP
 specification for further details.
 
+2.2 SNP_GET_DERIVED_KEY
+-----------------------
+:Technology: sev-snp
+:Type: guest ioctl
+:Parameters (in): struct snp_derived_key_req
+:Returns (out): struct snp_derived_key_resp on success, -negative on error
+
+The SNP_GET_DERIVED_KEY ioctl can be used to get a key derive from a root key.
+The derived key can be used by the guest for any purpose, such as sealing keys
+or communicating with external entities.
+
+The ioctl uses the SNP_GUEST_REQUEST (MSG_KEY_REQ) command provided by the
+SEV-SNP firmware to derive the key. See SEV-SNP specification for further details
+on the various fields passed in the key derivation request.
+
+On success, the snp_derived_key_resp.data contains the derived key value. See
+the SEV-SNP specification for further details.
 
 Reference
 ---------
diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
index 4fac82fd3e4c..2062f94fdc38 100644
--- a/drivers/virt/coco/sevguest/sevguest.c
+++ b/drivers/virt/coco/sevguest/sevguest.c
@@ -389,6 +389,48 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
 	return rc;
 }
 
+static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
+{
+	struct snp_guest_crypto *crypto = snp_dev->crypto;
+	struct snp_derived_key_resp resp = {0};
+	struct snp_derived_key_req req = {0};
+	int rc, resp_len;
+	/* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
+	u8 buf[64 + 16];
+
+	lockdep_assert_held(&snp_cmd_mutex);
+
+	if (!arg->req_data || !arg->resp_data)
+		return -EINVAL;
+
+	/*
+	 * The intermediate response buffer is used while decrypting the
+	 * response payload. Make sure that it has enough space to cover the
+	 * authtag.
+	 */
+	resp_len = sizeof(resp.data) + crypto->a_len;
+	if (sizeof(buf) < resp_len)
+		return -ENOMEM;
+
+	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+		return -EFAULT;
+
+	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
+				  SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len,
+				  &arg->fw_err);
+	if (rc)
+		return rc;
+
+	memcpy(resp.data, buf, sizeof(resp.data));
+	if (copy_to_user((void __user *)arg->resp_data, &resp, sizeof(resp)))
+		rc = -EFAULT;
+
+	/* The response buffer contains the sensitive data, explicitly clear it. */
+	memzero_explicit(buf, sizeof(buf));
+	memzero_explicit(&resp, sizeof(resp));
+	return rc;
+}
+
 static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 {
 	struct snp_guest_dev *snp_dev = to_snp_dev(file);
@@ -418,6 +460,9 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 	case SNP_GET_REPORT:
 		ret = get_report(snp_dev, &input);
 		break;
+	case SNP_GET_DERIVED_KEY:
+		ret = get_derived_key(snp_dev, &input);
+		break;
 	default:
 		break;
 	}
diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
index 38f11d723c68..598367f12064 100644
--- a/include/uapi/linux/sev-guest.h
+++ b/include/uapi/linux/sev-guest.h
@@ -30,6 +30,20 @@ struct snp_report_resp {
 	__u8 data[4000];
 };
 
+struct snp_derived_key_req {
+	__u32 root_key_select;
+	__u32 rsvd;
+	__u64 guest_field_select;
+	__u32 vmpl;
+	__u32 guest_svn;
+	__u64 tcb_version;
+};
+
+struct snp_derived_key_resp {
+	/* response data, see SEV-SNP spec for the format */
+	__u8 data[64];
+};
+
 struct snp_guest_request_ioctl {
 	/* message version number (must be non-zero) */
 	__u8 msg_version;
@@ -47,4 +61,7 @@ struct snp_guest_request_ioctl {
 /* Get SNP attestation report */
 #define SNP_GET_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x0, struct snp_guest_request_ioctl)
 
+/* Get a derived key from the root */
+#define SNP_GET_DERIVED_KEY _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x1, struct snp_guest_request_ioctl)
+
 #endif /* __UAPI_LINUX_SEV_GUEST_H_ */
-- 
2.25.1