[PATCH v2 5/6] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

TDX guest supports encrypted disk as root or secondary drives.
Decryption keys required to access such drives are usually maintained
by 3rd party key servers. Attestation is required by 3rd party key
servers to get the key for an encrypted disk volume, or possibly other
encrypted services. Attestation is used to prove to the key server that
the TD guest is running in a valid TD and the kernel and virtual BIOS
and other environment are secure.

During the boot process various components before the kernel accumulate
hashes in the TDX module, which can then combined into a report. This
would typically include a hash of the bios, bios configuration, boot
loader, command line, kernel, initrd.  After checking the hashes the
key server will securely release the keys.

The actual details of the attestation protocol depend on the particular
key server configuration, but some parts are common and need to
communicate with the TDX module.

This communication is implemented in the attestation driver.

The supported steps are:

  1. TD guest generates the TDREPORT that contains version information
     about the Intel TDX module, measurement of the TD, along with a
     TD-specified nonce.
  2. TD guest shares the TDREPORT with TD host via GetQuote hypercall
     which is used by the host to generate a quote via quoting
     enclave (QE).
  3. Quote generation completion notification is sent to TD OS via
     callback interrupt vector configured by TD using
     SetupEventNotifyInterrupt hypercall.
  4. After receiving the generated TDQUOTE, a remote verifier can be
     used to verify the quote and confirm the trustworthiness of the
     TD.

Attestation agent uses IOCTLs implemented by the attestation driver to
complete the various steps of the attestation process.

Also note that, explicit access permissions are not enforced in this
driver because the quote and measurements are not a secret. However
the access permissions of the device node can be used to set any
desired access policy. The udev default is usually root access
only.

TDX_CMD_GEN_QUOTE IOCTL can be used to create an computation on the
host, but TDX assumes that the host is able to deal with malicious
guest flooding it anyways.

The interaction with the TDX module is like a RPM protocol here. There
are several operations (get tdreport, get quote) that need to input a
blob, and then output another blob. 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
here. There is one ioctl per operation, that takes the input blob and
returns the output blob, and as well as auxiliary ioctls to return the
blob lengths. The ioctls are documented in the header file. 

Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 drivers/platform/x86/Kconfig            |   9 ++
 drivers/platform/x86/Makefile           |   1 +
 drivers/platform/x86/intel_tdx_attest.c | 171 ++++++++++++++++++++++++
 include/uapi/misc/tdx.h                 |  37 +++++
 4 files changed, 218 insertions(+)
 create mode 100644 drivers/platform/x86/intel_tdx_attest.c
 create mode 100644 include/uapi/misc/tdx.h

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index 60592fb88e7a..7d01c473aef6 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -1301,6 +1301,15 @@ config INTEL_SCU_IPC_UTIL
 	  low level access for debug work and updating the firmware. Say
 	  N unless you will be doing this on an Intel MID platform.
 
+config INTEL_TDX_ATTESTATION
+	tristate "Intel TDX attestation driver"
+	depends on INTEL_TDX_GUEST
+	help
+	  The TDX attestation driver provides IOCTL or MMAP interfaces to
+	  the user to request TDREPORT from the TDX module or request quote
+	  from VMM. It is mainly used to get secure disk decryption keys from
+	  the key server.
+
 config INTEL_TELEMETRY
 	tristate "Intel SoC Telemetry Driver"
 	depends on X86_64
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index dcc8cdb95b4d..83439990ae47 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -138,6 +138,7 @@ obj-$(CONFIG_INTEL_SCU_PCI)		+= intel_scu_pcidrv.o
 obj-$(CONFIG_INTEL_SCU_PLATFORM)	+= intel_scu_pltdrv.o
 obj-$(CONFIG_INTEL_SCU_WDT)		+= intel_scu_wdt.o
 obj-$(CONFIG_INTEL_SCU_IPC_UTIL)	+= intel_scu_ipcutil.o
+obj-$(CONFIG_INTEL_TDX_ATTESTATION)	+= intel_tdx_attest.o
 obj-$(CONFIG_INTEL_TELEMETRY)		+= intel_telemetry_core.o \
 					   intel_telemetry_pltdrv.o \
 					   intel_telemetry_debugfs.o
diff --git a/drivers/platform/x86/intel_tdx_attest.c b/drivers/platform/x86/intel_tdx_attest.c
new file mode 100644
index 000000000000..a0225d053851
--- /dev/null
+++ b/drivers/platform/x86/intel_tdx_attest.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * intel_tdx_attest.c - TDX guest attestation interface driver.
+ *
+ * Implements user interface to trigger attestation process and
+ * read the TD Quote result.
+ *
+ * Copyright (C) 2020 Intel Corporation
+ *
+ * Author:
+ *     Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
+ */
+
+#define pr_fmt(fmt) "x86/tdx: attest: " fmt
+
+#include <linux/module.h>
+#include <linux/miscdevice.h>
+#include <linux/uaccess.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/set_memory.h>
+#include <linux/io.h>
+#include <asm/apic.h>
+#include <asm/tdx.h>
+#include <asm/irq_vectors.h>
+#include <uapi/misc/tdx.h>
+
+#define VERSION				"1.0"
+
+/* Used in Quote memory allocation */
+#define QUOTE_SIZE			(2 * PAGE_SIZE)
+
+/* Mutex to synchronize attestation requests */
+static DEFINE_MUTEX(attestation_lock);
+/* Completion object to track attestation status */
+static DECLARE_COMPLETION(attestation_done);
+
+static void attestation_callback_handler(void)
+{
+	complete(&attestation_done);
+}
+
+static long tdg_attest_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long arg)
+{
+	u64 data = virt_to_phys(file->private_data);
+	void __user *argp = (void __user *)arg;
+	u8 *reportdata;
+	long ret = 0;
+
+	mutex_lock(&attestation_lock);
+
+	reportdata = kzalloc(TDX_TDREPORT_LEN, GFP_KERNEL);
+	if (!reportdata) {
+		mutex_unlock(&attestation_lock);
+		return -ENOMEM;
+	}
+
+	switch (cmd) {
+	case TDX_CMD_GET_TDREPORT:
+		if (copy_from_user(reportdata, argp, TDX_REPORT_DATA_LEN)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		/* Generate TDREPORT_STRUCT */
+		if (tdx_mcall_tdreport(data, virt_to_phys(reportdata))) {
+			ret = -EIO;
+			break;
+		}
+
+		if (copy_to_user(argp, file->private_data, TDX_TDREPORT_LEN))
+			ret = -EFAULT;
+		break;
+	case TDX_CMD_GEN_QUOTE:
+		if (copy_from_user(reportdata, argp, TDX_REPORT_DATA_LEN)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		/* Generate TDREPORT_STRUCT */
+		if (tdx_mcall_tdreport(data, virt_to_phys(reportdata))) {
+			ret = -EIO;
+			break;
+		}
+
+		ret = set_memory_decrypted((unsigned long)file->private_data,
+					   1UL << get_order(QUOTE_SIZE));
+		if (ret)
+			break;
+
+		/* Submit GetQuote Request */
+		if (tdx_hcall_get_quote(data)) {
+			ret = -EIO;
+			goto done;
+		}
+
+		/* Wait for attestation completion */
+		wait_for_completion_interruptible(&attestation_done);
+
+		if (copy_to_user(argp, file->private_data, QUOTE_SIZE))
+			ret = -EFAULT;
+done:
+		ret = set_memory_encrypted((unsigned long)file->private_data,
+					   1UL << get_order(QUOTE_SIZE));
+
+		break;
+	case TDX_CMD_GET_QUOTE_SIZE:
+		if (put_user(QUOTE_SIZE, (u64 __user *)argp))
+			ret = -EFAULT;
+
+		break;
+	default:
+		pr_err("cmd %d not supported\n", cmd);
+		break;
+	}
+
+	mutex_unlock(&attestation_lock);
+
+	kfree(reportdata);
+
+	return ret;
+}
+
+static int tdg_attest_open(struct inode *inode, struct file *file)
+{
+	/*
+	 * Currently tdg_event_notify_handler is only used in attestation
+	 * driver. But, WRITE_ONCE is used as benign data race notice.
+	 */
+	WRITE_ONCE(tdg_event_notify_handler, attestation_callback_handler);
+
+	file->private_data = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+						      get_order(QUOTE_SIZE));
+
+	return !file->private_data ? -ENOMEM : 0;
+}
+
+static int tdg_attest_release(struct inode *inode, struct file *file)
+{
+	/*
+	 * Currently tdg_event_notify_handler is only used in attestation
+	 * driver. But, WRITE_ONCE is used as benign data race notice.
+	 */
+	WRITE_ONCE(tdg_event_notify_handler, NULL);
+	free_pages((unsigned long)file->private_data, get_order(QUOTE_SIZE));
+	file->private_data = NULL;
+
+	return 0;
+}
+
+static const struct file_operations tdg_attest_fops = {
+	.owner		= THIS_MODULE,
+	.open		= tdg_attest_open,
+	.release	= tdg_attest_release,
+	.unlocked_ioctl	= tdg_attest_ioctl,
+	.llseek		= no_llseek,
+};
+
+static struct miscdevice tdg_attest_device = {
+	.minor          = MISC_DYNAMIC_MINOR,
+	.name           = "tdx-attest",
+	.fops           = &tdg_attest_fops,
+};
+module_misc_device(tdg_attest_device);
+
+MODULE_AUTHOR("Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>");
+MODULE_DESCRIPTION("TDX attestation driver ver " VERSION);
+MODULE_VERSION(VERSION);
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/misc/tdx.h b/include/uapi/misc/tdx.h
new file mode 100644
index 000000000000..59e6561c0892
--- /dev/null
+++ b/include/uapi/misc/tdx.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_MISC_TDX_H
+#define _UAPI_MISC_TDX_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+/* Input report data length for TDX_CMD_GET_TDREPORT IOCTL request */
+#define TDX_REPORT_DATA_LEN		64
+
+/* Output TD report data length after TDX_CMD_GET_TDREPORT IOCTL execution */
+#define TDX_TDREPORT_LEN		1024
+
+/*
+ * TDX_CMD_GET_TDREPORT IOCTL is used to get TDREPORT data from the TDX
+ * Module. Users should pass report data of size TDX_REPORT_DATA_LEN bytes
+ * via user input buffer of size TDX_TDREPORT_LEN. Once IOCTL is successful
+ * TDREPORT data is copied to the user buffer.
+ */
+#define TDX_CMD_GET_TDREPORT		_IOWR('T', 0x01, __u64)
+
+/*
+ * TDX_CMD_GEN_QUOTE IOCTL is used to request TD QUOTE from the VMM. User
+ * should pass report data of size TDX_REPORT_DATA_LEN bytes via user input
+ * buffer of quote size. Once IOCTL is successful quote data is copied back to
+ * the user buffer.
+ */
+#define TDX_CMD_GEN_QUOTE		_IOR('T', 0x02, __u64)
+
+/*
+ * TDX_CMD_GET_QUOTE_SIZE IOCTL is used to get the TD Quote size info in bytes.
+ * This will be used for determining the input buffer allocation size when
+ * using TDX_CMD_GEN_QUOTE IOCTL.
+ */
+#define TDX_CMD_GET_QUOTE_SIZE		_IOR('T', 0x03, __u64)
+
+#endif /* _UAPI_MISC_TDX_H */
-- 
2.25.1