misc: Add Nitro Secure Module driver

When running Linux inside a Nitro Enclave, the hypervisor provides a
special virtio device called "Nitro Security Module" (NSM). This device
has 3 main functions:

  1) Provide attestation reports
  2) Modify PCR state
  3) Provide entropy

This patch adds a driver for NSM that exposes a /dev/nsm device node which
user space can issue an ioctl on this device with raw NSM CBOR formatted
commands to request attestation documents, influence PCR states, read
entropy and enumerate status of the device. In addition, the driver
implements a hwrng backend.

Originally-by: Petre Eftime <petre.eftime@gmail.com>
Signed-off-by: Alexander Graf <graf@amazon.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231011213522.51781-1-graf@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 506 insertions, 0 deletions

diff --git a/drivers/misc/nsm.c b/drivers/misc/nsm.c
new file mode 100644
index 000000000000..0eaa3b4484bd
--- /dev/null
+++ b/drivers/misc/nsm.c
@@ -0,0 +1,506 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Amazon Nitro Secure Module driver.
+ *
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * The Nitro Secure Module implements commands via CBOR over virtio.
+ * This driver exposes a raw message ioctls on /dev/nsm that user
+ * space can use to issue these commands.
+ */
+
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/interrupt.h>
+#include <linux/hw_random.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <linux/uio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ids.h>
+#include <linux/virtio.h>
+#include <linux/wait.h>
+#include <uapi/linux/nsm.h>
+
+/* Timeout for NSM virtqueue respose in milliseconds. */
+#define NSM_DEFAULT_TIMEOUT_MSECS (120000) /* 2 minutes */
+
+/* Maximum length input data */
+struct nsm_data_req {
+	u32 len;
+	u8  data[NSM_REQUEST_MAX_SIZE];
+};
+
+/* Maximum length output data */
+struct nsm_data_resp {
+	u32 len;
+	u8  data[NSM_RESPONSE_MAX_SIZE];
+};
+
+/* Full NSM request/response message */
+struct nsm_msg {
+	struct nsm_data_req req;
+	struct nsm_data_resp resp;
+};
+
+struct nsm {
+	struct virtio_device *vdev;
+	struct virtqueue     *vq;
+	struct mutex          lock;
+	struct completion     cmd_done;
+	struct miscdevice     misc;
+	struct hwrng          hwrng;
+	struct work_struct    misc_init;
+	struct nsm_msg        msg;
+};
+
+/* NSM device ID */
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_NITRO_SEC_MOD, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct nsm *file_to_nsm(struct file *file)
+{
+	return container_of(file->private_data, struct nsm, misc);
+}
+
+static struct nsm *hwrng_to_nsm(struct hwrng *rng)
+{
+	return container_of(rng, struct nsm, hwrng);
+}
+
+#define CBOR_TYPE_MASK  0xE0
+#define CBOR_TYPE_MAP 0xA0
+#define CBOR_TYPE_TEXT 0x60
+#define CBOR_TYPE_ARRAY 0x40
+#define CBOR_HEADER_SIZE_SHORT 1
+
+#define CBOR_SHORT_SIZE_MAX_VALUE 23
+#define CBOR_LONG_SIZE_U8  24
+#define CBOR_LONG_SIZE_U16 25
+#define CBOR_LONG_SIZE_U32 26
+#define CBOR_LONG_SIZE_U64 27
+
+static bool cbor_object_is_array(const u8 *cbor_object, size_t cbor_object_size)
+{
+	if (cbor_object_size == 0 || cbor_object == NULL)
+		return false;
+
+	return (cbor_object[0] & CBOR_TYPE_MASK) == CBOR_TYPE_ARRAY;
+}
+
+static int cbor_object_get_array(u8 *cbor_object, size_t cbor_object_size, u8 **cbor_array)
+{
+	u8 cbor_short_size;
+	void *array_len_p;
+	u64 array_len;
+	u64 array_offset;
+
+	if (!cbor_object_is_array(cbor_object, cbor_object_size))
+		return -EFAULT;
+
+	cbor_short_size = (cbor_object[0] & 0x1F);
+
+	/* Decoding byte array length */
+	array_offset = CBOR_HEADER_SIZE_SHORT;
+	if (cbor_short_size >= CBOR_LONG_SIZE_U8)
+		array_offset += BIT(cbor_short_size - CBOR_LONG_SIZE_U8);
+
+	if (cbor_object_size < array_offset)
+		return -EFAULT;
+
+	array_len_p = &cbor_object[1];
+
+	switch (cbor_short_size) {
+	case CBOR_SHORT_SIZE_MAX_VALUE: /* short encoding */
+		array_len = cbor_short_size;
+		break;
+	case CBOR_LONG_SIZE_U8:
+		array_len = *(u8 *)array_len_p;
+		break;
+	case CBOR_LONG_SIZE_U16:
+		array_len = be16_to_cpup((__be16 *)array_len_p);
+		break;
+	case CBOR_LONG_SIZE_U32:
+		array_len = be32_to_cpup((__be32 *)array_len_p);
+		break;
+	case CBOR_LONG_SIZE_U64:
+		array_len = be64_to_cpup((__be64 *)array_len_p);
+		break;
+	}
+
+	if (cbor_object_size < array_offset)
+		return -EFAULT;
+
+	if (cbor_object_size - array_offset < array_len)
+		return -EFAULT;
+
+	if (array_len > INT_MAX)
+		return -EFAULT;
+
+	*cbor_array = cbor_object + array_offset;
+	return array_len;
+}
+
+/* Copy the request of a raw message to kernel space */
+static int fill_req_raw(struct nsm *nsm, struct nsm_data_req *req,
+			struct nsm_raw *raw)
+{
+	/* Verify the user input size. */
+	if (raw->request.len > sizeof(req->data))
+		return -EMSGSIZE;
+
+	/* Copy the request payload */
+	if (copy_from_user(req->data, u64_to_user_ptr(raw->request.addr),
+			   raw->request.len))
+		return -EFAULT;
+
+	req->len = raw->request.len;
+
+	return 0;
+}
+
+/* Copy the response of a raw message back to user-space */
+static int parse_resp_raw(struct nsm *nsm, struct nsm_data_resp *resp,
+			  struct nsm_raw *raw)
+{
+	/* Truncate any message that does not fit. */
+	raw->response.len = min_t(u64, raw->response.len, resp->len);
+
+	/* Copy the response content to user space */
+	if (copy_to_user(u64_to_user_ptr(raw->response.addr),
+			 resp->data, raw->response.len))
+		return -EFAULT;
+
+	return 0;
+}
+
+/* Virtqueue interrupt handler */
+static void nsm_vq_callback(struct virtqueue *vq)
+{
+	struct nsm *nsm = vq->vdev->priv;
+
+	complete(&nsm->cmd_done);
+}
+
+/* Forward a message to the NSM device and wait for the response from it */
+static int nsm_sendrecv_msg_locked(struct nsm *nsm)
+{
+	struct device *dev = &nsm->vdev->dev;
+	struct scatterlist sg_in, sg_out;
+	struct nsm_msg *msg = &nsm->msg;
+	struct virtqueue *vq = nsm->vq;
+	unsigned int len;
+	void *queue_buf;
+	bool kicked;
+	int rc;
+
+	/* Initialize scatter-gather lists with request and response buffers. */
+	sg_init_one(&sg_out, msg->req.data, msg->req.len);
+	sg_init_one(&sg_in, msg->resp.data, sizeof(msg->resp.data));
+
+	init_completion(&nsm->cmd_done);
+	/* Add the request buffer (read by the device). */
+	rc = virtqueue_add_outbuf(vq, &sg_out, 1, msg->req.data, GFP_KERNEL);
+	if (rc)
+		return rc;
+
+	/* Add the response buffer (written by the device). */
+	rc = virtqueue_add_inbuf(vq, &sg_in, 1, msg->resp.data, GFP_KERNEL);
+	if (rc)
+		goto cleanup;
+
+	kicked = virtqueue_kick(vq);
+	if (!kicked) {
+		/* Cannot kick the virtqueue. */
+		rc = -EIO;
+		goto cleanup;
+	}
+
+	/* If the kick succeeded, wait for the device's response. */
+	if (!wait_for_completion_io_timeout(&nsm->cmd_done,
+		msecs_to_jiffies(NSM_DEFAULT_TIMEOUT_MSECS))) {
+		rc = -ETIMEDOUT;
+		goto cleanup;
+	}
+
+	queue_buf = virtqueue_get_buf(vq, &len);
+	if (!queue_buf || (queue_buf != msg->req.data)) {
+		dev_err(dev, "wrong request buffer.");
+		rc = -ENODATA;
+		goto cleanup;
+	}
+
+	queue_buf = virtqueue_get_buf(vq, &len);
+	if (!queue_buf || (queue_buf != msg->resp.data)) {
+		dev_err(dev, "wrong response buffer.");
+		rc = -ENODATA;
+		goto cleanup;
+	}
+
+	msg->resp.len = len;
+
+	rc = 0;
+
+cleanup:
+	if (rc) {
+		/* Clean the virtqueue. */
+		while (virtqueue_get_buf(vq, &len) != NULL)
+			;
+	}
+
+	return rc;
+}
+
+static int fill_req_get_random(struct nsm *nsm, struct nsm_data_req *req)
+{
+	/*
+	 * 69                          # text(9)
+	 *     47657452616E646F6D      # "GetRandom"
+	 */
+	const u8 request[] = { CBOR_TYPE_TEXT + strlen("GetRandom"),
+			       'G', 'e', 't', 'R', 'a', 'n', 'd', 'o', 'm' };
+
+	memcpy(req->data, request, sizeof(request));
+	req->len = sizeof(request);
+
+	return 0;
+}
+
+static int parse_resp_get_random(struct nsm *nsm, struct nsm_data_resp *resp,
+				 void *out, size_t max)
+{
+	/*
+	 * A1                          # map(1)
+	 *     69                      # text(9) - Name of field
+	 *         47657452616E646F6D  # "GetRandom"
+	 * A1                          # map(1) - The field itself
+	 *     66                      # text(6)
+	 *         72616E646F6D        # "random"
+	 *	# The rest of the response is random data
+	 */
+	const u8 response[] = { CBOR_TYPE_MAP + 1,
+				CBOR_TYPE_TEXT + strlen("GetRandom"),
+				'G', 'e', 't', 'R', 'a', 'n', 'd', 'o', 'm',
+				CBOR_TYPE_MAP + 1,
+				CBOR_TYPE_TEXT + strlen("random"),
+				'r', 'a', 'n', 'd', 'o', 'm' };
+	struct device *dev = &nsm->vdev->dev;
+	u8 *rand_data = NULL;
+	u8 *resp_ptr = resp->data;
+	u64 resp_len = resp->len;
+	int rc;
+
+	if ((resp->len < sizeof(response) + 1) ||
+	    (memcmp(resp_ptr, response, sizeof(response)) != 0)) {
+		dev_err(dev, "Invalid response for GetRandom");
+		return -EFAULT;
+	}
+
+	resp_ptr += sizeof(response);
+	resp_len -= sizeof(response);
+
+	rc = cbor_object_get_array(resp_ptr, resp_len, &rand_data);
+	if (rc < 0) {
+		dev_err(dev, "GetRandom: Invalid CBOR encoding\n");
+		return rc;
+	}
+
+	rc = min_t(size_t, rc, max);
+	memcpy(out, rand_data, rc);
+
+	return rc;
+}
+
+/*
+ * HwRNG implementation
+ */
+static int nsm_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct nsm *nsm = hwrng_to_nsm(rng);
+	struct device *dev = &nsm->vdev->dev;
+	int rc = 0;
+
+	/* NSM always needs to wait for a response */
+	if (!wait)
+		return 0;
+
+	mutex_lock(&nsm->lock);
+
+	rc = fill_req_get_random(nsm, &nsm->msg.req);
+	if (rc != 0)
+		goto out;
+
+	rc = nsm_sendrecv_msg_locked(nsm);
+	if (rc != 0)
+		goto out;
+
+	rc = parse_resp_get_random(nsm, &nsm->msg.resp, data, max);
+	if (rc < 0)
+		goto out;
+
+	dev_dbg(dev, "RNG: returning rand bytes = %d", rc);
+out:
+	mutex_unlock(&nsm->lock);
+	return rc;
+}
+
+static long nsm_dev_ioctl(struct file *file, unsigned int cmd,
+	unsigned long arg)
+{
+	void __user *argp = u64_to_user_ptr((u64)arg);
+	struct nsm *nsm = file_to_nsm(file);
+	struct nsm_raw raw;
+	int r = 0;
+
+	if (cmd != NSM_IOCTL_RAW)
+		return -EINVAL;
+
+	if (_IOC_SIZE(cmd) != sizeof(raw))
+		return -EINVAL;
+
+	/* Copy user argument struct to kernel argument struct */
+	r = -EFAULT;
+	if (copy_from_user(&raw, argp, _IOC_SIZE(cmd)))
+		goto out;
+
+	mutex_lock(&nsm->lock);
+
+	/* Convert kernel argument struct to device request */
+	r = fill_req_raw(nsm, &nsm->msg.req, &raw);
+	if (r)
+		goto out;
+
+	/* Send message to NSM and read reply */
+	r = nsm_sendrecv_msg_locked(nsm);
+	if (r)
+		goto out;
+
+	/* Parse device response into kernel argument struct */
+	r = parse_resp_raw(nsm, &nsm->msg.resp, &raw);
+	if (r)
+		goto out;
+
+	/* Copy kernel argument struct back to user argument struct */
+	r = -EFAULT;
+	if (copy_to_user(argp, &raw, sizeof(raw)))
+		goto out;
+
+	r = 0;
+
+out:
+	mutex_unlock(&nsm->lock);
+	return r;
+}
+
+static int nsm_device_init_vq(struct virtio_device *vdev)
+{
+	struct virtqueue *vq = virtio_find_single_vq(vdev,
+		nsm_vq_callback, "nsm.vq.0");
+	struct nsm *nsm = vdev->priv;
+
+	if (IS_ERR(vq))
+		return PTR_ERR(vq);
+
+	nsm->vq = vq;
+
+	return 0;
+}
+
+static const struct file_operations nsm_dev_fops = {
+	.unlocked_ioctl = nsm_dev_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+};
+
+/* Handler for probing the NSM device */
+static int nsm_device_probe(struct virtio_device *vdev)
+{
+	struct device *dev = &vdev->dev;
+	struct nsm *nsm;
+	int rc;
+
+	nsm = devm_kzalloc(&vdev->dev, sizeof(*nsm), GFP_KERNEL);
+	if (!nsm)
+		return -ENOMEM;
+
+	vdev->priv = nsm;
+	nsm->vdev = vdev;
+
+	rc = nsm_device_init_vq(vdev);
+	if (rc) {
+		dev_err(dev, "queue failed to initialize: %d.\n", rc);
+		goto err_init_vq;
+	}
+
+	mutex_init(&nsm->lock);
+
+	/* Register as hwrng provider */
+	nsm->hwrng = (struct hwrng) {
+		.read = nsm_rng_read,
+		.name = "nsm-hwrng",
+		.quality = 1000,
+	};
+
+	rc = hwrng_register(&nsm->hwrng);
+	if (rc) {
+		dev_err(dev, "RNG initialization error: %d.\n", rc);
+		goto err_hwrng;
+	}
+
+	/* Register /dev/nsm device node */
+	nsm->misc = (struct miscdevice) {
+		.minor	= MISC_DYNAMIC_MINOR,
+		.name	= "nsm",
+		.fops	= &nsm_dev_fops,
+		.mode	= 0666,
+	};
+
+	rc = misc_register(&nsm->misc);
+	if (rc) {
+		dev_err(dev, "misc device registration error: %d.\n", rc);
+		goto err_misc;
+	}
+
+	return 0;
+
+err_misc:
+	hwrng_unregister(&nsm->hwrng);
+err_hwrng:
+	vdev->config->del_vqs(vdev);
+err_init_vq:
+	return rc;
+}
+
+/* Handler for removing the NSM device */
+static void nsm_device_remove(struct virtio_device *vdev)
+{
+	struct nsm *nsm = vdev->priv;
+
+	hwrng_unregister(&nsm->hwrng);
+
+	vdev->config->del_vqs(vdev);
+	misc_deregister(&nsm->misc);
+}
+
+/* NSM device configuration structure */
+static struct virtio_driver virtio_nsm_driver = {
+	.feature_table             = 0,
+	.feature_table_size        = 0,
+	.feature_table_legacy      = 0,
+	.feature_table_size_legacy = 0,
+	.driver.name               = KBUILD_MODNAME,
+	.driver.owner              = THIS_MODULE,
+	.id_table                  = id_table,
+	.probe                     = nsm_device_probe,
+	.remove                    = nsm_device_remove,
+};
+
+module_virtio_driver(virtio_nsm_driver);
+MODULE_DEVICE_TABLE(virtio, id_table);
+MODULE_DESCRIPTION("Virtio NSM driver");
+MODULE_LICENSE("GPL");