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Message-ID: <20220209181039.1262882-44-brijesh.singh@amd.com>
Date: Wed, 9 Feb 2022 12:10:37 -0600
From: Brijesh Singh <brijesh.singh@....com>
To: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<kvm@...r.kernel.org>, <linux-efi@...r.kernel.org>,
<platform-driver-x86@...r.kernel.org>,
<linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>
CC: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
Tom Lendacky <thomas.lendacky@....com>,
"H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
"Vitaly Kuznetsov" <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
"Andy Lutomirski" <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
"Peter Zijlstra" <peterz@...radead.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Dov Murik <dovmurik@...ux.ibm.com>,
Tobin Feldman-Fitzthum <tobin@....com>,
Borislav Petkov <bp@...en8.de>,
Michael Roth <michael.roth@....com>,
Vlastimil Babka <vbabka@...e.cz>,
"Kirill A . Shutemov" <kirill@...temov.name>,
Andi Kleen <ak@...ux.intel.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
<brijesh.ksingh@...il.com>, <tony.luck@...el.com>,
<marcorr@...gle.com>, <sathyanarayanan.kuppuswamy@...ux.intel.com>,
Brijesh Singh <brijesh.singh@....com>,
Liam Merwick <liam.merwick@...cle.com>
Subject: [PATCH v10 43/45] virt: sevguest: Add support to derive key
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@...cle.com>
Signed-off-by: Brijesh Singh <brijesh.singh@....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
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