Date:   Fri, 8 Nov 2019 22:17:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Jonathan Corbet <corbet@....net>,
        Felipe Balbi <balbi@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH 1/1] usb: gadget: add raw-gadget interface

On Fri, Nov 08, 2019 at 07:26:55PM +0100, Andrey Konovalov wrote:
> USB Raw Gadget is a kernel module that provides a userspace interface for
> the USB Gadget subsystem. Essentially it allows to emulate USB devices
> from userspace. Enabled with CONFIG_USB_RAW_GADGET. Raw Gadget is
> currently a strictly debugging feature and shouldn't be used in
> production.
> 
> Raw Gadget is similar to GadgetFS, but provides a more low-level and
> direct access to the USB Gadget layer for the userspace. The key
> differences are:
> 
> 1. Every USB request is passed to the userspace to get a response, while
>    GadgetFS responds to some USB requests internally based on the provided
>    descriptors. However note, that the UDC driver might respond to some
>    requests on its own and never forward them to the Gadget layer.
> 
> 2. GadgetFS performs some sanity checks on the provided USB descriptors,
>    while Raw Gadget allows you to provide arbitrary data as responses to
>    USB requests.
> 
> 3. Raw Gadget provides a way to select a UDC device/driver to bind to,
>    while GadgetFS currently binds to the first available UDC.
> 
> 4. Raw Gadget uses predictable endpoint names (handles) across different
>    UDCs (as long as UDCs have enough endpoints of each required transfer
>    type).
> 
> 5. Raw Gadget has ioctl-based interface instead of a filesystem-based one.

I like the idea, and you've shown that you can do neat stuff with this,
so that's a good proof-of-concept.

But, at the least, use a "real" char device node for this, not debugfs.
Switch this to a misc device and I'll be glad to review it.

Some minor nits that jump out at me other than debugfs:

> +static void raw_event_queue_destroy(struct raw_event_queue *queue)
> +{
> +	int i;
> +
> +	for (i = 0; i < queue->size; i++) {
> +		pr_debug("freeing event[%d] = %px\n", i, queue->events[i]);

You still have a lot of debugging messages in here.  Most of these can
be removed, as ftrace is useful instead now that you "know" the code
works properly.

> +		kfree(queue->events[i]);
> +	}
> +	queue->size = 0;
> +}
> +
> +/*----------------------------------------------------------------------*/
> +
> +struct raw_dev;
> +
> +#define USB_RAW_MAX_ENDPOINTS 32
> +
> +enum ep_state {
> +	STATE_EP_DISABLED,
> +	STATE_EP_ENABLED,
> +};
> +
> +struct raw_ep {
> +	struct raw_dev		*dev;
> +	enum ep_state		state;
> +	struct usb_ep		*ep;
> +	struct usb_request	*req;
> +	bool			urb_queued;
> +	bool			disabling;
> +	ssize_t			status;
> +};
> +
> +enum dev_state {
> +	STATE_DEV_INVALID = 0,
> +	STATE_DEV_OPENED,
> +	STATE_DEV_INITIALIZED,
> +	STATE_DEV_RUNNING,
> +	STATE_DEV_CLOSED,
> +	STATE_DEV_FAILED
> +};
> +
> +struct raw_dev {
> +	refcount_t			count;

Why not just use a "real" struct device?

Or a kref at the least, no need to roll your own refcount logic here,
right?

> +	spinlock_t			lock;
> +
> +	const char			*udc_name;
> +	struct usb_gadget_driver	driver;
> +
> +	/* Protected by lock: */
> +	enum dev_state			state;
> +	bool				gadget_registered;
> +	struct usb_gadget		*gadget;
> +	struct usb_request		*req;
> +	bool				ep0_in_pending;
> +	bool				ep0_out_pending;
> +	bool				ep0_urb_queued;
> +	ssize_t				ep0_status;
> +	struct raw_ep			eps[USB_RAW_MAX_ENDPOINTS];
> +
> +	struct completion		ep0_done;
> +	struct raw_event_queue		queue;
> +};
> +
> +static struct raw_dev *dev_new(void)
> +{
> +	struct raw_dev *dev;
> +
> +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +	if (!dev)
> +		return NULL;
> +	refcount_set(&dev->count, 1); /* Matches dev_put() in raw_release(). */
> +	spin_lock_init(&dev->lock);
> +	init_completion(&dev->ep0_done);
> +	raw_event_queue_init(&dev->queue);
> +	pr_debug("device created\n");
> +	return dev;
> +}
> +
> +static inline void dev_get(struct raw_dev *dev)
> +{
> +	refcount_inc(&dev->count);
> +}
> +
> +static void dev_put(struct raw_dev *dev)
> +{
> +	int i;
> +
> +	if (likely(!refcount_dec_and_test(&dev->count)))
> +		return;

unless you can measure it, don't use likely/unlikely as the compiler and
cpu can almost always get it right instead.

> +	kfree(dev->udc_name);
> +	kfree(dev->driver.udc_name);
> +	if (dev->req) {
> +		if (dev->ep0_urb_queued)
> +			usb_ep_dequeue(dev->gadget->ep0, dev->req);
> +		usb_ep_free_request(dev->gadget->ep0, dev->req);
> +	}
> +	raw_event_queue_destroy(&dev->queue);
> +	for (i = 0; i < USB_RAW_MAX_ENDPOINTS; i++) {
> +		if (dev->eps[i].state != STATE_EP_ENABLED)
> +			continue;
> +		usb_ep_disable(dev->eps[i].ep);
> +		usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
> +		kfree(dev->eps[i].ep->desc);
> +		dev->eps[i].state = STATE_EP_DISABLED;
> +	}
> +	kfree(dev);
> +	pr_debug("device freed\n");

ftrace :)

> +static void gadget_unbind(struct usb_gadget *gadget)
> +{
> +	struct raw_dev *dev = get_gadget_data(gadget);
> +	unsigned long flags;
> +
> +	if (WARN_ON(!dev))
> +		return;

Why warn?  How can this happen?

> +	spin_lock_irqsave(&dev->lock, flags);
> +	set_gadget_data(gadget, NULL);
> +	spin_unlock_irqrestore(&dev->lock, flags);
> +	dev_put(dev); /* Matches dev_get() in gadget_bind(). */
> +	pr_debug("unbound\n");
> +}
> +
> +static int gadget_setup(struct usb_gadget *gadget,
> +			const struct usb_ctrlrequest *ctrl)
> +{
> +	int ret = 0;
> +	struct raw_dev *dev = get_gadget_data(gadget);
> +	unsigned long flags;
> +
> +	pr_debug("bRequestType: 0x%x (%s), bRequest: 0x%x,\n"
> +		"                   wValue: 0x%x, wIndex: 0x%x, wLength: %d\n",
> +		ctrl->bRequestType,
> +		(ctrl->bRequestType & USB_DIR_IN) ? "IN" : "OUT",
> +		ctrl->bRequest, ctrl->wValue, ctrl->wIndex, ctrl->wLength);
> +
> +	if (WARN_ON(!dev))
> +		return -ENODEV;

Same here.

> +	spin_lock_irqsave(&dev->lock, flags);
> +	if (dev->state != STATE_DEV_RUNNING) {
> +		pr_err("ignoring, device is not running\n");
> +		ret = -ENODEV;
> +		goto out_unlock;
> +	}
> +	pr_debug("in_pending: %d, out_pending: %d\n",
> +			dev->ep0_in_pending, dev->ep0_out_pending);
> +	if (dev->ep0_in_pending || dev->ep0_out_pending) {
> +		pr_debug("stalling, already have pending request\n");
> +		ret = -EBUSY;
> +		goto out_unlock;
> +	}
> +	if ((ctrl->bRequestType & USB_DIR_IN) && ctrl->wLength) {
> +		pr_debug("ep0_in_pending <= true\n");
> +		dev->ep0_in_pending = true;
> +	} else {
> +		pr_debug("ep0_out_pending <= true\n");
> +		dev->ep0_out_pending = true;
> +	}
> +	spin_unlock_irqrestore(&dev->lock, flags);
> +
> +	ret = raw_queue_event(dev, USB_RAW_EVENT_CONTROL, sizeof(*ctrl), ctrl);
> +	if (ret < 0)
> +		pr_err("failed to queue event\n");
> +	pr_debug("event queued\n");
> +	goto out;
> +
> +out_unlock:
> +	spin_unlock_irqrestore(&dev->lock, flags);
> +out:
> +	return ret;
> +}
> +
> +static void gadget_disconnect(struct usb_gadget *gadget)
> +{
> +	pr_debug("ignoring\n");
> +}
> +
> +static void gadget_suspend(struct usb_gadget *gadget)
> +{
> +	pr_debug("ignoring\n");
> +}
> +
> +static void gadget_resume(struct usb_gadget *gadget)
> +{
> +	pr_debug("ignoring\n");
> +}
> +
> +static void gadget_reset(struct usb_gadget *gadget)
> +{
> +	pr_debug("ignoring\n");
> +}

I think you don't even need functions for these, right?  If not, just
remove.  If you do, we should fix the gadget core to not require them :)

> +
> +/*----------------------------------------------------------------------*/
> +
> +static int raw_open(struct inode *inode, struct file *fd)
> +{
> +	struct raw_dev *dev;
> +
> +	dev = dev_new();
> +	if (!dev) {
> +		pr_err("failed to created device");

So many error messages printed on failures, you only needed the original
one if memory was gone that the core sent out.

> +		return -ENOMEM;
> +	}
> +	fd->private_data = dev;
> +	dev->state = STATE_DEV_OPENED;
> +	pr_debug("device opened");
> +	return 0;
> +}
> +
> +static int raw_release(struct inode *inode, struct file *fd)
> +{
> +	int ret = 0;
> +	struct raw_dev *dev = fd->private_data;
> +	unsigned long flags;
> +	bool unregister = false;
> +
> +	if (!dev)
> +		return -EBUSY;

How can that happen?

> +
> +	spin_lock_irqsave(&dev->lock, flags);
> +	dev->state = STATE_DEV_CLOSED;
> +	pr_debug("device is closed\n");
> +	if (!dev->gadget) {
> +		spin_unlock_irqrestore(&dev->lock, flags);
> +		goto out_put;
> +	}
> +	if (dev->gadget_registered)
> +		unregister = true;
> +	dev->gadget_registered = false;
> +	spin_unlock_irqrestore(&dev->lock, flags);
> +
> +	if (unregister) {
> +		ret = usb_gadget_unregister_driver(&dev->driver);
> +		WARN_ON(ret != 0);
> +		dev_put(dev); /* Matches dev_get() in raw_ioctl_run(). */
> +	}
> +
> +out_put:
> +	dev_put(dev); /* Matches dev_new() in raw_open(). */
> +	pr_debug("device released");
> +	return ret;
> +}
> +
> +/*----------------------------------------------------------------------*/
> +
> +#define UDC_NAME_LENGTH_MAX 128
> +
> +static int raw_ioctl_init(struct raw_dev *dev, unsigned long value)
> +{
> +	int ret = 0;
> +	struct usb_raw_init arg;
> +	char *udc_driver_name;
> +	char *udc_device_name;
> +	unsigned long flags;
> +
> +	ret = copy_from_user(&arg, (void __user *)value, sizeof(arg));
> +	if (ret)
> +		return ret;
> +
> +	switch (arg.speed) {
> +	case USB_SPEED_LOW:
> +	case USB_SPEED_FULL:
> +	case USB_SPEED_HIGH:
> +	case USB_SPEED_SUPER:
> +		break;
> +	default:
> +		arg.speed = USB_SPEED_HIGH;
> +	}
> +
> +	udc_driver_name = kmalloc(UDC_NAME_LENGTH_MAX, GFP_KERNEL);
> +	if (!udc_driver_name)
> +		return -ENOMEM;
> +	ret = strncpy_from_user(udc_driver_name, arg.driver_name,
> +					UDC_NAME_LENGTH_MAX);
> +	if (ret < 0) {
> +		kfree(udc_driver_name);
> +		return ret;
> +	}
> +	ret = 0;
> +	pr_debug("udc_driver_name: %s\n", udc_driver_name);
> +
> +	udc_device_name = kmalloc(UDC_NAME_LENGTH_MAX, GFP_KERNEL);
> +	if (!udc_device_name) {
> +		kfree(udc_driver_name);
> +		return -ENOMEM;
> +	}
> +	ret = strncpy_from_user(udc_device_name, arg.device_name,
> +					UDC_NAME_LENGTH_MAX);

You are burying the max size of names in the .c code, put it in the .h
to give userspace a chance.

> +static bool check_ep_caps(struct usb_ep *ep,
> +				struct usb_endpoint_descriptor *desc)
> +{
> +	switch (desc->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) {
> +	case USB_ENDPOINT_XFER_ISOC:

We have functions/macros for endpoint types, right?  Can't you use them
here?

> +		if (!ep->caps.type_iso)
> +			return false;
> +		break;
> +	case USB_ENDPOINT_XFER_BULK:
> +		if (!ep->caps.type_bulk)
> +			return false;
> +		break;
> +	case USB_ENDPOINT_XFER_INT:
> +		if (!ep->caps.type_int)
> +			return false;
> +		break;
> +	default:
> +		return false;
> +	}
> +
> +	switch (desc->bEndpointAddress & USB_ENDPOINT_DIR_MASK) {
> +	case USB_DIR_IN:

Same here, we have macros for this.

> +static int __init raw_init(void)
> +{
> +	raw_file = debugfs_create_file("raw-gadget", 0600,
> +			usb_debug_root, NULL, &raw_ops);
> +	if (!raw_file) {

this return value will never be NULL no matter what.  So you just tested
for an impossiblity :)

In the future, there's never a new to check any return value for any
debugfs calls, it's not an issue.

> +		pr_err("failed to create raw-gadget in debugfs\n");
> +		return -ENOMEM;
> +	}
> +	return 0;
> +}
> +
> +static void __exit raw_exit(void)
> +{
> +	if (!raw_file)
> +		return;

No need to check:

> +	debugfs_remove(raw_file);

that call can take NULL

> +	raw_file = NULL;

No need for this :)

> +/*
> + * struct usb_raw_init - argument for USB_RAW_IOCTL_INIT ioctl.
> + * @speed: The speed of the emulated USB device, takes the same values as
> + *     the usb_device_speed enum: USB_SPEED_FULL, USB_SPEED_HIGH, etc.
> + * @driver_name: The name of the UDC driver.
> + * @device_name: The name of a UDC instance.
> + *
> + * The last two fields identify a UDC the gadget driver should bind to.
> + * For example, Dummy UDC has "dummy_udc" as its driver_name and "dummy_udc.N"
> + * as its device_name, where N in the index of the Dummy UDC instance.
> + * At the same time the dwc2 driver that is used on Raspberry Pi Zero, has
> + * "20980000.usb" as both driver_name and device_name.
> + */
> +struct usb_raw_init {
> +	uint64_t	speed;
> +	const char	*driver_name;
> +	const char	*device_name;

If you have structures crossing the user/kernel boundry, always use the
correct data types.  Those start with "__".  So this would be __u32 and
__u8 * instead.

> +};
> +
> +/* The type of event fetched with the USB_RAW_IOCTL_EVENT_FETCH ioctl. */
> +enum usb_raw_event_type {
> +	USB_RAW_EVENT_INVALID,
> +
> +	/* This event is queued when the driver has bound to a UDC. */
> +	USB_RAW_EVENT_CONNECT,
> +
> +	/* This event is queued when a new control request arrived to ep0. */
> +	USB_RAW_EVENT_CONTROL,
> +
> +	/* The list might grow in the future. */
> +};
> +
> +/*
> + * struct usb_raw_event - argument for USB_RAW_IOCTL_EVENT_FETCH ioctl.
> + * @type: The type of the fetched event.
> + * @length: Length of the data buffer. Updated by the driver and set to the
> + *     actual length of the fetched event data.
> + * @data: A buffer to store the fetched event data.
> + *
> + * Currently the fetched data buffer is empty for USB_RAW_EVENT_CONNECT,
> + * and contains struct usb_ctrlrequest for USB_RAW_EVENT_CONTROL.
> + */
> +struct usb_raw_event {
> +	uint32_t	type;
> +	uint32_t	length;
> +	char		data[0];

__u32 please.

> +};
> +
> +#define USB_RAW_IO_FLAGS_ZERO	0x0001
> +#define USB_RAW_IO_FLAGS_MASK	0x0001
> +
> +static int usb_raw_io_flags_valid(uint16_t flags)
> +{
> +	return (flags & ~USB_RAW_IO_FLAGS_MASK) == 0;
> +}
> +
> +static int usb_raw_io_flags_zero(uint16_t flags)
> +{
> +	return (flags & USB_RAW_IO_FLAGS_ZERO);
> +}
> +
> +/*
> + * struct usb_raw_ep_io - argument for USB_RAW_IOCTL_EP0/EP_WRITE/READ ioctls.
> + * @ep: Endpoint handle as returned by USB_RAW_IOCTL_EP_ENABLE for
> + *     USB_RAW_IOCTL_EP_WRITE/READ. Ignored for USB_RAW_IOCTL_EP0_WRITE/READ.
> + * @flags: When USB_RAW_IO_FLAGS_ZERO is specified, the zero flag is set on
> + *     the submitted USB request, see include/linux/usb/gadget.h for details.
> + * @length: Length of data.
> + * @data: Data to send for USB_RAW_IOCTL_EP0/EP_WRITE. Buffer to store received
> + *     data for USB_RAW_IOCTL_EP0/EP_READ.
> + */
> +struct usb_raw_ep_io {
> +	uint16_t	ep;
> +	uint16_t	flags;

__u16

> +	uint32_t	length;
> +	char		data[0];
> +};
> +
> +/*
> + * Initializes a Raw Gadget instance.
> + * Accepts a pointer to the usb_raw_init struct as an argument.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_INIT		_IOW('U', 0, struct usb_raw_init)
> +
> +/*
> + * Instructs Raw Gadget to bind to a UDC and start emulating a USB device.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_RUN		_IO('U', 1)
> +
> +/*
> + * A blocking ioctl that waits for an event and returns fetched event data to
> + * the user.
> + * Accepts a pointer to the usb_raw_event struct.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_EVENT_FETCH	_IOR('U', 2, struct usb_raw_event)
> +
> +/*
> + * Queues an IN (OUT for READ) urb as a response to the last control request
> + * received on endpoint 0, provided that was an IN (OUT for READ) request and
> + * waits until the urb is completed. Copies received data to user for READ.
> + * Accepts a pointer to the usb_raw_ep_io struct as an argument.
> + * Returns length of trasferred data on success or negative error code on
> + * failure.
> + */
> +#define USB_RAW_IOCTL_EP0_WRITE		_IOW('U', 3, struct usb_raw_ep_io)
> +#define USB_RAW_IOCTL_EP0_READ		_IOWR('U', 4, struct usb_raw_ep_io)
> +
> +/*
> + * Finds an endpoint that supports the transfer type specified in the
> + * descriptor and enables it.
> + * Accepts a pointer to the usb_endpoint_descriptor struct as an argument.
> + * Returns enabled endpoint handle on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_EP_ENABLE		_IOW('U', 5, struct usb_endpoint_descriptor)
> +
> +/* Disables specified endpoint.
> + * Accepts endpoint handle as an argument.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_EP_DISABLE	_IOW('U', 6, int)

__u32, right?


> +
> +/*
> + * Queues an IN (OUT for READ) urb as a response to the last control request
> + * received on endpoint usb_raw_ep_io.ep, provided that was an IN (OUT for READ)
> + * request and waits until the urb is completed. Copies received data to user
> + * for READ.
> + * Accepts a pointer to the usb_raw_ep_io struct as an argument.
> + * Returns length of trasferred data on success or negative error code on
> + * failure.
> + */
> +#define USB_RAW_IOCTL_EP_WRITE		_IOW('U', 7, struct usb_raw_ep_io)
> +#define USB_RAW_IOCTL_EP_READ		_IOWR('U', 8, struct usb_raw_ep_io)
> +
> +/*
> + * Switches the gadget into the configured state.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_CONFIGURE		_IO('U', 9)
> +
> +/*
> + * Constrains UDC VBUS power usage.
> + * Accepts current limit in 2 mA units as an argument.
> + * Returns 0 on success or negative error code on failure.
> + */
> +#define USB_RAW_IOCTL_VBUS_DRAW		_IOW('U', 10, uint32_t)

__u32

thanks,

greg k-h

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