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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Mon, 24 Feb 2020 17:17:58 +0100
Message-ID: <CAAeHK+y7yKwQP-prUv17gFXKnKtBdfz7fQ8Gc5vwL49R4yCHuA@mail.gmail.com>
Subject: Re: [PATCH v6 0/1] usb: gadget: add raw-gadget interface
To:     Felipe Balbi <balbi@kernel.org>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Alan Stern <stern@rowland.harvard.edu>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Mon, Feb 24, 2020 at 5:13 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> This patchset (currently a single patch) adds a new userspace interface
> for the USB Gadget subsystem called USB Raw Gadget. This is what is
> currently being used to enable coverage-guided USB fuzzing with syzkaller:
>
> https://github.com/google/syzkaller/blob/master/docs/linux/external_fuzzing_usb.md
>
> Initially I was using GadgetFS (together with the Dummy HCD/UDC module)
> to perform emulation of USB devices for fuzzing, but later switched to a
> custom written interface. The incentive to implement a different interface
> was to provide a somewhat raw and direct access to the USB Gadget layer
> for the userspace, where every USB request is passed to the userspace to
> get a response. See documentation for the list of differences between
> Raw Gadget and GadgetFS.
>
> Currently Raw Gadget only supports blocking I/O mode, that synchronously
> waits for the result of each operation to allow collecting coverage per
> operation.
>
> This patchset has been pushed to the public Linux kernel Gerrit instance:
>
> https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/2144
>
> Changes v5 -> v6:
> - Prevent raw_process_ep_io() racing with raw_ioctl_ep_disable() by
>   checking urb_queued flag in the latter.
> - Use GFP_KERNEL instead of GFP_ATOMIC where possible.
> - Reject opening raw-gadget with O_NONBLOCK to allow future extensions to
>   support nonblocking IO.
> - Reduce RAW_EVENT_QUEUE_SIZE to 16.

Hi Felipe! I'm still hoping for a review :)

(Forgot to add a link to the example that emulates a USB keyboard via
Raw Gadget into the cover letter:

https://github.com/xairy/raw-gadget/blob/master/examples/keyboard.c)

>
> Changes v4 -> v5:
> - Specified explicit usb_raw_event_type enum values for all entries.
> - Dropped pointless locking in gadget_unbind().
>
> Changes v3 -> v4:
> - Print debug message when maxpacket check fails.
> - Use module_misc_device() instead of module_init/exit().
> - Reuse DRIVER_NAME macro in raw_device struct definition.
> - Don't print WARNING in raw_release().
> - Add comment that explains locking into raw_event_queue_fetch().
> - Print a WARNING when event queue size is exceeded.
> - Rename raw.c to raw_gadget.c.
> - Mention module name in Kconfig.
> - Reworked logging to use dev_err/dbg() instead of pr_err/debug().
>
> Changes v2 -> v3:
> - Updated device path in documentation.
> - Changed usb_raw_init struct layout to make it the same for 32 bit compat
>   mode.
> - Added compat_ioctl to raw_fops.
> - Changed raw_ioctl_init() to return EINVAL for invalid USB speeds, except
>   for USB_SPEED_UNKNOWN, which defaults to USB_SPEED_HIGH.
> - Reject endpoints with maxpacket = 0 in raw_ioctl_ep_enable().
>
> Changes v1 -> v2:
> - Moved raw.c to legacy/.
> - Changed uapi header to use __u* types.
> - Switched from debugfs entry to a misc device.
> - Changed raw_dev from refcount to kref.
> - Moved UDC_NAME_LENGTH_MAX to uapi headers.
> - Used usb_endpoint_type() and usb_endpoint_dir_in/out() functions instead
>   of open coding them.
> - Added "WITH Linux-syscall-note" to SPDX id in the uapi header.
> - Removed pr_err() if case dev_new() fails.
> - Reduced the number of debugging messages.
>
> Andrey Konovalov (1):
>   usb: gadget: add raw-gadget interface
>
>  Documentation/usb/index.rst            |    1 +
>  Documentation/usb/raw-gadget.rst       |   61 ++
>  drivers/usb/gadget/legacy/Kconfig      |   11 +
>  drivers/usb/gadget/legacy/Makefile     |    1 +
>  drivers/usb/gadget/legacy/raw_gadget.c | 1078 ++++++++++++++++++++++++
>  include/uapi/linux/usb/raw_gadget.h    |  167 ++++
>  6 files changed, 1319 insertions(+)
>  create mode 100644 Documentation/usb/raw-gadget.rst
>  create mode 100644 drivers/usb/gadget/legacy/raw_gadget.c
>  create mode 100644 include/uapi/linux/usb/raw_gadget.h
>
> --
> 2.25.0.265.gbab2e86ba0-goog
>