usb: gadget: add WebUSB landing page support

There is a custom (non-USB IF) extension to the USB standard:

https://wicg.github.io/webusb/

This specification is published under the W3C Community Contributor
Agreement, which in particular allows to implement the specification
without any royalties.

The specification allows USB gadgets to announce an URL to landing
page and describes a Javascript interface for websites to interact
with the USB gadget, if the user allows it. It is currently
supported by Chromium-based browsers, such as Chrome, Edge and
Opera on all major operating systems including Linux.

This patch adds optional support for Linux-based USB gadgets
wishing to expose such a landing page.

During device enumeration, a host recognizes that the announced
USB version is at least 2.01, which means, that there are BOS
descriptors available. The device than announces WebUSB support
using a platform device capability. This includes a vendor code
under which the landing page URL can be retrieved using a
vendor-specific request.

Previously, the BOS descriptors would unconditionally include an
LPM related descriptor, as BOS descriptors were only ever sent
when the device was LPM capable. As this is no longer the case,
this patch puts this descriptor behind a lpm_capable condition.

Usage is modeled after os_desc descriptors:
echo 1 > webusb/use
echo "https://www.kernel.org" > webusb/landingPage

lsusb will report the device with the following lines:
  Platform Device Capability:
    bLength                24
    bDescriptorType        16
    bDevCapabilityType      5
    bReserved               0
    PlatformCapabilityUUID    {3408b638-09a9-47a0-8bfd-a0768815b665}
      WebUSB:
        bcdVersion    1.00
        bVendorCode      0
        iLandingPage     1 https://www.kernel.org

Signed-off-by: Jó Ágila Bitsch <jgilab@gmail.com>
Link: https://lore.kernel.org/r/Y8Crf8P2qAWuuk/F@jo-einhundert
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 90 insertions, 0 deletions

diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
index 43ac3fa760db..91d22c3ed458 100644
--- a/include/linux/usb/composite.h
+++ b/include/linux/usb/composite.h
@@ -25,6 +25,7 @@
 #include <linux/version.h>
 #include <linux/usb/ch9.h>
 #include <linux/usb/gadget.h>
+#include <linux/usb/webusb.h>
 #include <linux/log2.h>
 #include <linux/configfs.h>
 
@@ -474,6 +475,12 @@ struct usb_composite_dev {
 	struct usb_configuration	*os_desc_config;
 	unsigned int			use_os_string:1;
 
+	/* WebUSB */
+	u16				bcd_webusb_version;
+	u8				b_webusb_vendor_code;
+	char				landing_page[WEBUSB_URL_RAW_MAX_LENGTH];
+	unsigned int			use_webusb:1;
+
 	/* private: */
 	/* internals */
 	unsigned int			suspended:1;
diff --git a/include/linux/usb/webusb.h b/include/linux/usb/webusb.h
new file mode 100644
index 000000000000..b430d84357f3
--- /dev/null
+++ b/include/linux/usb/webusb.h
@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * WebUSB descriptors and constants
+ *
+ * Copyright (C) 2023 Jó Ágila Bitsch <jgilab@gmail.com>
+ */
+
+#ifndef	__LINUX_USB_WEBUSB_H
+#define	__LINUX_USB_WEBUSB_H
+
+#include "uapi/linux/usb/ch9.h"
+
+/*
+ * little endian PlatformCapablityUUID for WebUSB
+ * 3408b638-09a9-47a0-8bfd-a0768815b665
+ * to identify Platform Device Capability descriptors as referring to WebUSB
+ *
+ * the UUID above MUST be sent over the wire as the byte sequence:
+ * {0x38, 0xB6, 0x08, 0x34, 0xA9, 0x09, 0xA0, 0x47, 0x8B, 0xFD, 0xA0, 0x76, 0x88, 0x15, 0xB6, 0x65}.
+ */
+#define WEBUSB_UUID \
+	UUID_INIT(0x38b60834, 0xa909, 0xa047, 0x8b, 0xfd, 0xa0, 0x76, 0x88, 0x15, 0xb6, 0x65)
+
+/*
+ * WebUSB Platform Capability data
+ *
+ * A device announces support for the
+ * WebUSB command set by including the following Platform Descriptor Data in its
+ * Binary Object Store associated with the WebUSB_UUID above.
+ * See: https://wicg.github.io/webusb/#webusb-platform-capability-descriptor
+ */
+struct usb_webusb_cap_data {
+	__le16 bcdVersion;
+#define WEBUSB_VERSION_1_00	cpu_to_le16(0x0100) /* currently only version 1.00 is defined */
+	u8  bVendorCode;
+	u8  iLandingPage;
+#define WEBUSB_LANDING_PAGE_NOT_PRESENT	0
+#define WEBUSB_LANDING_PAGE_PRESENT	1 /* we chose the fixed index 1 for the URL descriptor */
+} __packed;
+
+#define USB_WEBUSB_CAP_DATA_SIZE	4
+
+/*
+ * Get URL Request
+ *
+ * The request to fetch an URL is defined in https://wicg.github.io/webusb/#get-url as:
+ * bmRequestType: (USB_DIR_IN | USB_TYPE_VENDOR) = 11000000B
+ * bRequest: bVendorCode
+ * wValue: iLandingPage
+ * wIndex: GET_URL = 2
+ * wLength: Descriptor Length (typically U8_MAX = 255)
+ * Data: URL Descriptor
+ */
+#define WEBUSB_GET_URL 2
+
+/*
+ * This descriptor contains a single URL and is returned by the Get URL request.
+ *
+ * See: https://wicg.github.io/webusb/#url-descriptor
+ */
+struct webusb_url_descriptor {
+	u8  bLength;
+#define WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH	3
+	u8  bDescriptorType;
+#define WEBUSB_URL_DESCRIPTOR_TYPE		3
+	u8  bScheme;
+#define WEBUSB_URL_SCHEME_HTTP			0
+#define WEBUSB_URL_SCHEME_HTTPS			1
+#define WEBUSB_URL_SCHEME_NONE			255
+	u8  URL[U8_MAX - WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH];
+} __packed;
+
+/*
+ * Buffer size to hold the longest URL that can be in an URL descriptor
+ *
+ * The descriptor can be U8_MAX  bytes long.
+ * WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH bytes are used for a header.
+ * Since the longest prefix that might be stripped is "https://", we may accommodate an additional
+ * 8 bytes.
+ */
+#define WEBUSB_URL_RAW_MAX_LENGTH (U8_MAX - WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + 8)
+
+#endif /* __LINUX_USB_USBNET_H */