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Subject[PATCH v3] 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>
---
v2 -> V3: improved commit message to include additional condition in desc_bos as per comment
by Alan Stern
V1 -> V2: cleaned up coding style, made URL scheme comparison case insensitive, addressed review
comments by Alan Stern
V0 -> V1: use sysfs_emit instead of sprintf and use lock in webusb_bcdVersion_store, addressed review
comments by Christophe JAILLET

Documentation/ABI/testing/configfs-usb-gadget | 13 ++
drivers/usb/gadget/composite.c | 95 ++++++++++--
drivers/usb/gadget/configfs.c | 145 ++++++++++++++++++
include/linux/usb/composite.h | 6 +
include/uapi/linux/usb/ch9.h | 33 ++++
5 files changed, 282 insertions(+), 10 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-usb-gadget b/Documentation/ABI/testing/configfs-usb-gadget
index b7943aa7e997..8399e0f0ed1c 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget
+++ b/Documentation/ABI/testing/configfs-usb-gadget
@@ -143,3 +143,16 @@ Description:
qw_sign an identifier to be reported as "OS String"
proper
============= ===============================================
+
+What: /config/usb-gadget/gadget/webusb
+Date: Dec 2022
+KernelVersion: 6.2
+Description:
+ This group contains "WebUSB" extension handling attributes.
+
+ ============= ===============================================
+ use flag turning "WebUSB" support on/off
+ bcdVersion bcd WebUSB specification version number
+ b_vendor_code one-byte value used for custom per-device
+ landing_page UTF-8 encoded URL of the device's landing page
+ ============= ===============================================
diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 403563c06477..9b209e69442d 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -14,6 +14,7 @@
#include <linux/device.h>
#include <linux/utsname.h>
#include <linux/bitfield.h>
+#include <linux/uuid.h>

#include <linux/usb/composite.h>
#include <linux/usb/otg.h>
@@ -713,14 +714,16 @@ static int bos_desc(struct usb_composite_dev *cdev)
* A SuperSpeed device shall include the USB2.0 extension descriptor
* and shall support LPM when operating in USB2.0 HS mode.
*/
- usb_ext = cdev->req->buf + le16_to_cpu(bos->wTotalLength);
- bos->bNumDeviceCaps++;
- le16_add_cpu(&bos->wTotalLength, USB_DT_USB_EXT_CAP_SIZE);
- usb_ext->bLength = USB_DT_USB_EXT_CAP_SIZE;
- usb_ext->bDescriptorType = USB_DT_DEVICE_CAPABILITY;
- usb_ext->bDevCapabilityType = USB_CAP_TYPE_EXT;
- usb_ext->bmAttributes = cpu_to_le32(USB_LPM_SUPPORT |
- USB_BESL_SUPPORT | besl);
+ if (cdev->gadget->lpm_capable) {
+ usb_ext = cdev->req->buf + le16_to_cpu(bos->wTotalLength);
+ bos->bNumDeviceCaps++;
+ le16_add_cpu(&bos->wTotalLength, USB_DT_USB_EXT_CAP_SIZE);
+ usb_ext->bLength = USB_DT_USB_EXT_CAP_SIZE;
+ usb_ext->bDescriptorType = USB_DT_DEVICE_CAPABILITY;
+ usb_ext->bDevCapabilityType = USB_CAP_TYPE_EXT;
+ usb_ext->bmAttributes = cpu_to_le32(USB_LPM_SUPPORT |
+ USB_BESL_SUPPORT | besl);
+ }

/*
* The Superspeed USB Capability descriptor shall be implemented by all
@@ -821,6 +824,40 @@ static int bos_desc(struct usb_composite_dev *cdev)
}
}

+ /*
+ * Following the specifaction at:
+ * https://wicg.github.io/webusb/#webusb-platform-capability-descriptor
+ */
+ if (cdev->use_webusb) {
+ struct usb_webusb_cap_descriptor *webusb_cap;
+ /*
+ * little endian PlatformCapablityUUID for WebUSB:
+ * 3408b638-09a9-47a0-8bfd-a0768815b665
+ */
+ uuid_t webusb_uuid = UUID_INIT(0x38b60834, 0xa909, 0xa047, 0x8b, 0xfd, 0xa0, 0x76,
+ 0x88, 0x15, 0xb6, 0x65);
+
+ webusb_cap = cdev->req->buf + le16_to_cpu(bos->wTotalLength);
+ bos->bNumDeviceCaps++;
+
+ le16_add_cpu(&bos->wTotalLength, USB_DT_WEBUSB_SIZE);
+ webusb_cap->bLength = USB_DT_WEBUSB_SIZE;
+ webusb_cap->bDescriptorType = USB_DT_DEVICE_CAPABILITY;
+ webusb_cap->bDevCapabilityType = USB_PLAT_DEV_CAP_TYPE;
+ webusb_cap->bReserved = 0;
+ export_uuid(webusb_cap->UUID, &webusb_uuid);
+ if (cdev->bcd_webusb_version != 0)
+ webusb_cap->bcdVersion = cpu_to_le16(cdev->bcd_webusb_version);
+ else
+ webusb_cap->bcdVersion = cpu_to_le16(0x0100);
+
+ webusb_cap->bVendorCode = cdev->b_webusb_vendor_code;
+ if (strnlen(cdev->landing_page, sizeof(cdev->landing_page)) > 0)
+ webusb_cap->iLandingPage = 1;
+ else
+ webusb_cap->iLandingPage = 0;
+ }
+
return le16_to_cpu(bos->wTotalLength);
}

@@ -1744,7 +1781,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
cdev->desc.bcdUSB = cpu_to_le16(0x0210);
}
} else {
- if (gadget->lpm_capable)
+ if (gadget->lpm_capable || cdev->use_webusb)
cdev->desc.bcdUSB = cpu_to_le16(0x0201);
else
cdev->desc.bcdUSB = cpu_to_le16(0x0200);
@@ -1779,7 +1816,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
break;
case USB_DT_BOS:
if (gadget_is_superspeed(gadget) ||
- gadget->lpm_capable) {
+ gadget->lpm_capable || cdev->use_webusb) {
value = bos_desc(cdev);
value = min(w_length, (u16) value);
}
@@ -2013,6 +2050,44 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
goto check_value;
}

+ /*
+ * webusb descriptor handling, following:
+ * https://wicg.github.io/webusb/#device-requests
+ */
+ if (cdev->use_webusb &&
+ (ctrl->bRequestType & USB_TYPE_VENDOR) &&
+ ctrl->wIndex == /* WEBUSB_GET_URL*/ 2 &&
+ ctrl->bRequest == cdev->b_webusb_vendor_code) {
+ /*
+ * specification of the url descriptor in WebUSB:
+ * https://wicg.github.io/webusb/#webusb-descriptors
+ */
+ u8 *buf;
+ unsigned int landing_page_length;
+
+ buf = cdev->req->buf;
+ buf[1] = /* WEBUSB_URL*/ 3;
+
+ landing_page_length = strnlen(cdev->landing_page, 252);
+ if (strncasecmp("https://", cdev->landing_page, 8) == 0) {
+ buf[2] = 0x01;
+ memcpy(buf+3, cdev->landing_page+8, landing_page_length-8);
+ buf[0] = landing_page_length - 8 + 3;
+ } else if (strncasecmp("http://", cdev->landing_page, 7) == 0) {
+ buf[2] = 0x00;
+ memcpy(buf+3, cdev->landing_page+7, landing_page_length-7);
+ buf[0] = landing_page_length - 7 + 3;
+ } else {
+ buf[2] = 0xFF;
+ memcpy(buf+3, cdev->landing_page, landing_page_length);
+ buf[0] = landing_page_length + 3;
+ }
+
+ value = buf[0];
+
+ goto check_value;
+ }
+
VDBG(cdev,
"non-core control req%02x.%02x v%04x i%04x l%d\n",
ctrl->bRequestType, ctrl->bRequest,
diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 96121d1c8df4..2b7f01a9efff 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -39,6 +39,7 @@ struct gadget_info {
struct config_group configs_group;
struct config_group strings_group;
struct config_group os_desc_group;
+ struct config_group webusb_group;

struct mutex lock;
struct usb_gadget_strings *gstrings[MAX_USB_STRING_LANGS + 1];
@@ -50,6 +51,11 @@ struct gadget_info {
bool use_os_desc;
char b_vendor_code;
char qw_sign[OS_STRING_QW_SIGN_LEN];
+ bool use_webusb;
+ u16 bcd_webusb_version;
+ u8 b_webusb_vendor_code;
+ char landing_page[255];
+
spinlock_t spinlock;
bool unbind;
};
@@ -780,6 +786,131 @@ static void gadget_strings_attr_release(struct config_item *item)
USB_CONFIG_STRING_RW_OPS(gadget_strings);
USB_CONFIG_STRINGS_LANG(gadget_strings, gadget_info);

+static inline struct gadget_info *webusb_item_to_gadget_info(
+ struct config_item *item)
+{
+ return container_of(to_config_group(item),
+ struct gadget_info, webusb_group);
+}
+
+static ssize_t webusb_use_show(struct config_item *item, char *page)
+{
+ return sysfs_emit(page, "%d\n",
+ webusb_item_to_gadget_info(item)->use_webusb);
+}
+
+static ssize_t webusb_use_store(struct config_item *item, const char *page,
+ size_t len)
+{
+ struct gadget_info *gi = webusb_item_to_gadget_info(item);
+ int ret;
+ bool use;
+
+ mutex_lock(&gi->lock);
+ ret = kstrtobool(page, &use);
+ if (!ret) {
+ gi->use_webusb = use;
+ ret = len;
+ }
+ mutex_unlock(&gi->lock);
+
+ return ret;
+}
+
+static ssize_t webusb_bcdVersion_show(struct config_item *item, char *page)
+{
+ return sysfs_emit(page, "0x%04x\n",
+ webusb_item_to_gadget_info(item)->bcd_webusb_version);
+}
+
+static ssize_t webusb_bcdVersion_store(struct config_item *item,
+ const char *page, size_t len)
+{
+ struct gadget_info *gi = webusb_item_to_gadget_info(item);
+ u16 bcdVersion;
+ int ret;
+
+ mutex_lock(&gi->lock);
+ ret = kstrtou16(page, 0, &bcdVersion);
+ if (ret)
+ goto out;
+ ret = is_valid_bcd(bcdVersion);
+ if (ret)
+ goto out;
+
+ gi->bcd_webusb_version = bcdVersion;
+ ret = len;
+
+out:
+ mutex_unlock(&gi->lock);
+
+ return ret;
+}
+
+static ssize_t webusb_bVendorCode_show(struct config_item *item, char *page)
+{
+ return sysfs_emit(page, "0x%02x\n",
+ webusb_item_to_gadget_info(item)->b_webusb_vendor_code);
+}
+
+static ssize_t webusb_bVendorCode_store(struct config_item *item,
+ const char *page, size_t len)
+{
+ struct gadget_info *gi = webusb_item_to_gadget_info(item);
+ int ret;
+ u8 b_vendor_code;
+
+ mutex_lock(&gi->lock);
+ ret = kstrtou8(page, 0, &b_vendor_code);
+ if (!ret) {
+ gi->b_webusb_vendor_code = b_vendor_code;
+ ret = len;
+ }
+ mutex_unlock(&gi->lock);
+
+ return ret;
+}
+
+static ssize_t webusb_landingPage_show(struct config_item *item, char *page)
+{
+ return sysfs_emit(page, "%s\n", webusb_item_to_gadget_info(item)->landing_page);
+}
+
+static ssize_t webusb_landingPage_store(struct config_item *item, const char *page,
+ size_t len)
+{
+ struct gadget_info *gi = webusb_item_to_gadget_info(item);
+ int l;
+
+ l = min(len, sizeof(gi->landing_page));
+ if (page[l - 1] == '\n')
+ --l;
+
+ mutex_lock(&gi->lock);
+ memcpy(gi->landing_page, page, l);
+ mutex_unlock(&gi->lock);
+
+ return len;
+}
+
+CONFIGFS_ATTR(webusb_, use);
+CONFIGFS_ATTR(webusb_, bVendorCode);
+CONFIGFS_ATTR(webusb_, bcdVersion);
+CONFIGFS_ATTR(webusb_, landingPage);
+
+static struct configfs_attribute *webusb_attrs[] = {
+ &webusb_attr_use,
+ &webusb_attr_bcdVersion,
+ &webusb_attr_bVendorCode,
+ &webusb_attr_landingPage,
+ NULL,
+};
+
+static struct config_item_type webusb_type = {
+ .ct_attrs = webusb_attrs,
+ .ct_owner = THIS_MODULE,
+};
+
static inline struct gadget_info *os_desc_item_to_gadget_info(
struct config_item *item)
{
@@ -1341,6 +1472,16 @@ static int configfs_composite_bind(struct usb_gadget *gadget,
gi->cdev.desc.iSerialNumber = s[USB_GADGET_SERIAL_IDX].id;
}

+ if (gi->use_webusb) {
+ cdev->use_webusb = true;
+ cdev->bcd_webusb_version = gi->bcd_webusb_version;
+ cdev->b_webusb_vendor_code = gi->b_webusb_vendor_code;
+ memcpy(cdev->landing_page, gi->landing_page,
+ strnlen(gi->landing_page,
+ min(sizeof(cdev->landing_page),
+ sizeof(gi->landing_page))));
+ }
+
if (gi->use_os_desc) {
cdev->use_os_string = true;
cdev->b_vendor_code = gi->b_vendor_code;
@@ -1605,6 +1746,10 @@ static struct config_group *gadgets_make(
&os_desc_type);
configfs_add_default_group(&gi->os_desc_group, &gi->group);

+ config_group_init_type_name(&gi->webusb_group, "webusb",
+ &webusb_type);
+ configfs_add_default_group(&gi->webusb_group, &gi->group);
+
gi->composite.bind = configfs_do_nothing;
gi->composite.unbind = configfs_do_nothing;
gi->composite.suspend = NULL;
diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
index 43ac3fa760db..eb6fac5bbcde 100644
--- a/include/linux/usb/composite.h
+++ b/include/linux/usb/composite.h
@@ -474,6 +474,12 @@ 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[255];
+ unsigned int use_webusb:1;
+
/* private: */
/* internals */
unsigned int suspended:1;
diff --git a/include/uapi/linux/usb/ch9.h b/include/uapi/linux/usb/ch9.h
index 31fcfa084e63..3a36550297bc 100644
--- a/include/uapi/linux/usb/ch9.h
+++ b/include/uapi/linux/usb/ch9.h
@@ -947,6 +947,39 @@ struct usb_ss_container_id_descriptor {

#define USB_DT_USB_SS_CONTN_ID_SIZE 20

+/*
+ * Platform Device Capability descriptor: Defines platform specific device
+ * capabilities
+ */
+#define USB_PLAT_DEV_CAP_TYPE 5
+struct usb_plat_dev_cap_descriptor {
+ __u8 bLength;
+ __u8 bDescriptorType;
+ __u8 bDevCapabilityType;
+ __u8 bReserved;
+ __u8 UUID[16];
+} __attribute__((packed));
+
+#define USB_DT_USB_PLAT_DEV_CAP_SIZE 20
+
+/*
+ * WebUSB Platform Capability descriptor: A device announces support for the
+ * WebUSB command set by including the following Platform Descriptor in its
+ * Binary Object Store
+ * https://wicg.github.io/webusb/#webusb-platform-capability-descriptor
+ */
+struct usb_webusb_cap_descriptor {
+ __u8 bLength;
+ __u8 bDescriptorType;
+ __u8 bDevCapabilityType;
+ __u8 bReserved;
+ __u8 UUID[16];
+ __u16 bcdVersion;
+ __u8 bVendorCode;
+ __u8 iLandingPage;
+} __attribute__((packed));
+#define USB_DT_WEBUSB_SIZE (USB_DT_USB_PLAT_DEV_CAP_SIZE + 4)
+
/*
* SuperSpeed Plus USB Capability descriptor: Defines the set of
* SuperSpeed Plus USB specific device level capabilities
--
2.37.2
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