nsm.c

// 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,
	.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");