virt: Add TDX guest driver

TDX guest driver exposes IOCTL interfaces to service TDX guest
user-specific requests. Currently, it is only used to allow the user to
get the TDREPORT to support TDX attestation.

Details about the TDX attestation process are documented in
Documentation/x86/tdx.rst, and the IOCTL details are documented in
Documentation/virt/coco/tdx-guest.rst.

Operations like getting TDREPORT involves sending a blob of data as
input and getting another blob of data as output. It was considered
to use a sysfs interface for this, but it doesn't fit well into the
standard sysfs model for configuring values. It would be possible to
do read/write on files, but it would need multiple file descriptors,
which would be somewhat messy. IOCTLs seems to be the best fitting
and simplest model for this use case. The AMD sev-guest driver also
uses IOCTL interface to support attestation.

[Bagas Sanjaya: Ack is for documentation portion]
Acked-by: Kai Huang <kai.huang@intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Wander Lairson Costa <wander@redhat.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Documentation/virt/coco/tdx-guest.rst

@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================================================
+TDX Guest API Documentation
+===================================================================
+
+1. General description
+======================
+
+The TDX guest driver exposes IOCTL interfaces via /dev/tdx-guest misc
+device to allow userspace to get certain TDX guest specific details.
+
+2. API description
+==================
+
+In this section, for each supported IOCTL, following information is
+provided along with a generic description.
+
+:Input parameters: Parameters passed to the IOCTL and related details.
+:Output: Details about output data and return value (with details about the non
+         common error values).
+
+2.1 TDX_CMD_GET_REPORT
+----------------------
+
+:Input parameters: struct tdx_report_req
+:Output: Upon successful execution, TDREPORT data is copied to
+         tdx_report_req.tdreport and return 0. Return -EIO on
+         TDCALL failure or standard error number on other common
+         failures.
+
+The TDX_CMD_GET_REPORT IOCTL can be used by the attestation software to
+get the TDREPORT from the TDX module using TDCALL[TDG.MR.REPORT].
+
+Reference
+---------
+
+TDX reference material is collected here:
+
+https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
+
+The driver is based on TDX module specification v1.0 and TDX GHCI specification v1.0.

Documentation/virt/index.rst

@@ -14,6 +14,7 @@ Linux Virtualization Support
    ne_overview
    acrn/index
    coco/sev-guest
+   coco/tdx-guest
    hyperv/index
 
 .. only:: html and subproject

Documentation/x86/tdx.rst

@@ -210,6 +210,49 @@ converted to shared on boot.
 For coherent DMA allocation, the DMA buffer gets converted on the
 allocation. Check force_dma_unencrypted() for details.
 
+Attestation
+===========
+
+Attestation is used to verify the TDX guest trustworthiness to other
+entities before provisioning secrets to the guest. For example, a key
+server may want to use attestation to verify that the guest is the
+desired one before releasing the encryption keys to mount the encrypted
+rootfs or secondary drive.
+
+The TDX module records the state of the TDX guest in various stages of
+the guest boot process using build time measurement register (MRTD) and
+runtime measurement registers (RTMR). Measurements related to guest
+initial configuration and firmware image are recorded in the MRTD
+register. Measurements related to initial state, kernel image, firmware
+image, command line options, initrd, ACPI tables, etc are recorded in
+RTMR registers. For more details as an example, please refer to TDX
+Virtual Firmware design specification, sec titled "TD Measurement". At
+TDX guest runtime, the attestation process is used to attest to these
+measurements.
+
+The attestation process consists of two steps: TDREPORT generation and
+Quote generation.
+
+TDX guest uses TDCALL[TDG.MR.REPORT] to get the TDREPORT (TDREPORT_STRUCT)
+from the TDX module. TDREPORT is a fixed-size data structure generated by
+the TDX module which contains guest-specific information (such as build
+and boot measurements), platform security version, and the MAC to protect
+the integrity of the TDREPORT. A user-provided 64-Byte REPORTDATA is used
+as input and included in the TDREPORT. Typically it can be some nonce
+provided by attestation service so the TDREPORT can be verified uniquely.
+More details about the TDREPORT can be found in Intel TDX Module
+specification, section titled "TDG.MR.REPORT Leaf".
+
+After getting the TDREPORT, the second step of the attestation process
+is to send it to the Quoting Enclave (QE) to generate the Quote. TDREPORT
+by design can only be verified on the local platform as the MAC key is
+bound to the platform. To support remote verification of the TDREPORT,
+TDX leverages Intel SGX Quoting Enclave to verify the TDREPORT locally
+and convert it to a remotely verifiable Quote. Method of sending TDREPORT
+to QE is implementation specific. Attestation software can choose
+whatever communication channel available (i.e. vsock or TCP/IP) to
+send the TDREPORT to QE and receive the Quote.
+
 References
 ==========
 

arch/x86/include/asm/tdx.h

@@ -21,6 +21,7 @@
 /* TDX module Call Leaf IDs */
 #define TDX_GET_INFO			1
 #define TDX_GET_VEINFO			3
+#define TDX_GET_REPORT			4
 #define TDX_ACCEPT_PAGE			6
 
 #ifndef __ASSEMBLY__

drivers/virt/Kconfig

@@ -52,4 +52,6 @@ source "drivers/virt/coco/efi_secret/Kconfig"
 
 source "drivers/virt/coco/sev-guest/Kconfig"
 
+source "drivers/virt/coco/tdx-guest/Kconfig"
+
 endif

drivers/virt/Makefile

@@ -11,3 +11,4 @@ obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
 obj-$(CONFIG_ACRN_HSM)		+= acrn/
 obj-$(CONFIG_EFI_SECRET)	+= coco/efi_secret/
 obj-$(CONFIG_SEV_GUEST)		+= coco/sev-guest/
+obj-$(CONFIG_INTEL_TDX_GUEST)	+= coco/tdx-guest/

drivers/virt/coco/tdx-guest/Kconfig

@@ -0,0 +1,10 @@
+config TDX_GUEST_DRIVER
+	tristate "TDX Guest driver"
+	depends on INTEL_TDX_GUEST
+	help
+	  The driver provides userspace interface to communicate with
+	  the TDX module to request the TDX guest details like attestation
+	  report.
+
+	  To compile this driver as module, choose M here. The module will
+	  be called tdx-guest.

drivers/virt/coco/tdx-guest/Makefile

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_TDX_GUEST_DRIVER) += tdx-guest.o

drivers/virt/coco/tdx-guest/tdx-guest.c

@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * TDX guest user interface driver
+ *
+ * Copyright (C) 2022 Intel Corporation
+ */
+
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+
+#include <uapi/linux/tdx-guest.h>
+
+#include <asm/cpu_device_id.h>
+#include <asm/tdx.h>
+
+static long tdx_get_report(void __user *argp)
+{
+	u8 *reportdata, *tdreport;
+	struct tdx_report_req req;
+	long ret;
+
+	if (copy_from_user(&req, argp, sizeof(req)))
+		return -EFAULT;
+
+	/*
+	 * Per TDX Module 1.0 specification, section titled
+	 * "TDG.MR.REPORT", REPORTDATA length is fixed as
+	 * TDX_REPORTDATA_LEN, TDREPORT length is fixed as
+	 * TDX_REPORT_LEN, and TDREPORT subtype is fixed as 0.
+	 */
+	if (req.subtype || req.rpd_len != TDX_REPORTDATA_LEN ||
+	    req.tdr_len != TDX_REPORT_LEN)
+		return -EINVAL;
+
+	if (memchr_inv(req.reserved, 0, sizeof(req.reserved)))
+		return -EINVAL;
+
+	reportdata = kmalloc(req.rpd_len, GFP_KERNEL);
+	if (!reportdata)
+		return -ENOMEM;
+
+	tdreport = kzalloc(req.tdr_len, GFP_KERNEL);
+	if (!tdreport) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (copy_from_user(reportdata, u64_to_user_ptr(req.reportdata),
+			   req.rpd_len)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	/*
+	 * Generate TDREPORT using "TDG.MR.REPORT" TDCALL.
+	 *
+	 * Get the TDREPORT using REPORTDATA as input. Refer to
+	 * section 22.3.3 TDG.MR.REPORT leaf in the TDX Module 1.0
+	 * Specification for detailed information.
+	 */
+	ret = __tdx_module_call(TDX_GET_REPORT, virt_to_phys(tdreport),
+				virt_to_phys(reportdata), req.subtype,
+				0, NULL);
+	if (ret) {
+		ret = -EIO;
+		goto out;
+	}
+
+	if (copy_to_user(u64_to_user_ptr(req.tdreport), tdreport, req.tdr_len))
+		ret = -EFAULT;
+
+out:
+	kfree(reportdata);
+	kfree(tdreport);
+
+	return ret;
+}
+
+static long tdx_guest_ioctl(struct file *file, unsigned int cmd,
+			    unsigned long arg)
+{
+	switch (cmd) {
+	case TDX_CMD_GET_REPORT:
+		return tdx_get_report((void __user *)arg);
+	default:
+		return -ENOTTY;
+	}
+}
+
+static const struct file_operations tdx_guest_fops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = tdx_guest_ioctl,
+	.llseek = no_llseek,
+};
+
+static struct miscdevice tdx_misc_dev = {
+	.name = TDX_GUEST_DEVICE,
+	.minor = MISC_DYNAMIC_MINOR,
+	.fops = &tdx_guest_fops,
+};
+
+static int __init tdx_guest_init(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return -ENODEV;
+
+	return misc_register(&tdx_misc_dev);
+}
+module_init(tdx_guest_init);
+
+static void __exit tdx_guest_exit(void)
+{
+	misc_deregister(&tdx_misc_dev);
+}
+module_exit(tdx_guest_exit);
+
+static const struct x86_cpu_id tdx_guest_ids[] = {
+	X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
+
+MODULE_AUTHOR("Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>");
+MODULE_DESCRIPTION("TDX Guest Driver");
+MODULE_LICENSE("GPL");

include/uapi/linux/tdx-guest.h

@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_TDX_GUEST_H_
+#define _UAPI_LINUX_TDX_GUEST_H_
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+#define TDX_GUEST_DEVICE                "tdx-guest"
+
+/* Length of the REPORTDATA used in TDG.MR.REPORT TDCALL */
+#define TDX_REPORTDATA_LEN              64
+
+/* Length of TDREPORT used in TDG.MR.REPORT TDCALL */
+#define TDX_REPORT_LEN                  1024
+
+/**
+ * struct tdx_report_req - Get TDREPORT using REPORTDATA as input.
+ *
+ * @reportdata: User-defined REPORTDATA to be included into TDREPORT.
+ *	Typically it can be some nonce provided by attestation service,
+ *	so the generated TDREPORT can be uniquely verified.
+ * @tdreport: TDREPORT output from TDCALL[TDG.MR.REPORT].
+ * @rpd_len: Length of the REPORTDATA (fixed as 64 bytes by the TDX
+ *	Module specification, but a parameter is added to handle future
+ *	extension).
+ * @tdr_len: Length of the TDREPORT (fixed as 1024 bytes by the TDX
+ *	Module specification, but a parameter is added to accommodate
+ *	future extension).
+ * @subtype: Subtype of TDREPORT (fixed as 0 by the TDX Module specification,
+ *	but added a parameter to handle future extension).
+ * @reserved: Reserved entries to handle future requirements. Should be
+ *	filled with zeroes.
+ *
+ * Used in TDX_CMD_GET_REPORT IOCTL request.
+ */
+struct tdx_report_req {
+	__u64 reportdata;
+	__u64 tdreport;
+	__u32 rpd_len;
+	__u32 tdr_len;
+	__u8 subtype;
+	__u8 reserved[7];
+};
+
+/*
+ * TDX_CMD_GET_REPORT - Get TDREPORT using TDCALL[TDG.MR.REPORT]
+ *
+ * Return 0 on success, -EIO on TDCALL execution failure, and
+ * standard errno on other general error cases.
+ */
+#define TDX_CMD_GET_REPORT              _IOWR('T', 1, struct tdx_report_req)
+
+#endif /* _UAPI_LINUX_TDX_GUEST_H_ */