virt: Add SEV-SNP guest driver

The SEV-SNP specification provides the guest a mechanism to communicate
with the PSP without risk from a malicious hypervisor who wishes to
read, alter, drop or replay the messages sent. The driver uses
snp_issue_guest_request() to issue GHCB SNP_GUEST_REQUEST or
SNP_EXT_GUEST_REQUEST NAE events to submit the request to PSP.

The PSP requires that all communication should be encrypted using key
specified through a struct snp_guest_platform_data descriptor.

Userspace can use SNP_GET_REPORT ioctl() to query the guest attestation
report.

See SEV-SNP spec section Guest Messages for more details.

  [ bp: Remove the "what" from the commit message, massage. ]

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-44-brijesh.singh@amd.com

include/uapi/linux/sev-guest.h

@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note */
+/*
+ * Userspace interface for AMD SEV and SNP guest driver.
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Brijesh Singh <brijesh.singh@amd.com>
+ *
+ * SEV API specification is available at: https://developer.amd.com/sev/
+ */
+
+#ifndef __UAPI_LINUX_SEV_GUEST_H_
+#define __UAPI_LINUX_SEV_GUEST_H_
+
+#include <linux/types.h>
+
+struct snp_report_req {
+	/* user data that should be included in the report */
+	__u8 user_data[64];
+
+	/* The vmpl level to be included in the report */
+	__u32 vmpl;
+
+	/* Must be zero filled */
+	__u8 rsvd[28];
+};
+
+struct snp_report_resp {
+	/* response data, see SEV-SNP spec for the format */
+	__u8 data[4000];
+};
+
+struct snp_guest_request_ioctl {
+	/* message version number (must be non-zero) */
+	__u8 msg_version;
+
+	/* Request and response structure address */
+	__u64 req_data;
+	__u64 resp_data;
+
+	/* firmware error code on failure (see psp-sev.h) */
+	__u64 fw_err;
+};
+
+#define SNP_GUEST_REQ_IOC_TYPE	'S'
+
+/* Get SNP attestation report */
+#define SNP_GET_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x0, struct snp_guest_request_ioctl)
+
+#endif /* __UAPI_LINUX_SEV_GUEST_H_ */