From 12fc84e8c4288cc8ed5f14a35e077130c2cfece2 Mon Sep 17 00:00:00 2001 From: Elbert Mai Date: Mon, 4 Mar 2024 16:23:01 -0800 Subject: [PATCH] usb: Export BOS descriptor to sysfs Motivation ---------- The binary device object store (BOS) of a USB device consists of the BOS descriptor followed by a set of device capability descriptors. One that is of interest to users is the platform descriptor. This contains a 128-bit UUID and arbitrary data, and it allows parties outside of USB-IF to add additional metadata about a USB device in a standards-compliant manner. Notable examples include the WebUSB and Microsoft OS 2.0 descriptors. The kernel already retrieves and caches the BOS from USB devices if its bcdUSB is >= 0x0201. Because the BOS is flexible and extensible, we export the entire BOS to sysfs so users can retrieve whatever device capabilities they desire, without requiring USB I/O or elevated permissions. Implementation -------------- Add bos_descriptors attribute to sysfs. This is a binary file and it works the same way as the existing descriptors attribute. The file exists only if the BOS is present in the USB device. Also create a binary attribute group, so the driver core can handle the creation of both the descriptors and bos_descriptors attributes in sysfs. Signed-off-by: Elbert Mai Link: https://lore.kernel.org/r/20240305002301.95323-1-code@elbertmai.com Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/sysfs-bus-usb | 10 ++++ drivers/usb/core/sysfs.c | 78 +++++++++++++++++++------ 2 files changed, 71 insertions(+), 17 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb index 2b7108e21977..af9b653422f1 100644 --- a/Documentation/ABI/testing/sysfs-bus-usb +++ b/Documentation/ABI/testing/sysfs-bus-usb @@ -442,6 +442,16 @@ What: /sys/bus/usb/devices/usbX/descriptors Description: Contains the interface descriptors, in binary. +What: /sys/bus/usb/devices/usbX/bos_descriptors +Date: March 2024 +Contact: Elbert Mai +Description: + Binary file containing the cached binary device object store (BOS) + of the device. This consists of the BOS descriptor followed by the + set of device capability descriptors. All descriptors read from + this file are in bus-endian format. Note that the kernel will not + request the BOS from a device if its bcdUSB is less than 0x0201. + What: /sys/bus/usb/devices/usbX/idProduct Description: Product ID, in hexadecimal. diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c index e67826ec053e..777526f59720 100644 --- a/drivers/usb/core/sysfs.c +++ b/drivers/usb/core/sysfs.c @@ -849,16 +849,10 @@ static const struct attribute_group dev_string_attr_grp = { .is_visible = dev_string_attrs_are_visible, }; -const struct attribute_group *usb_device_groups[] = { - &dev_attr_grp, - &dev_string_attr_grp, - NULL -}; - /* Binary descriptors */ static ssize_t -read_descriptors(struct file *filp, struct kobject *kobj, +descriptors_read(struct file *filp, struct kobject *kobj, struct bin_attribute *attr, char *buf, loff_t off, size_t count) { @@ -880,7 +874,7 @@ read_descriptors(struct file *filp, struct kobject *kobj, srclen = sizeof(struct usb_device_descriptor); } else { src = udev->rawdescriptors[cfgno]; - srclen = __le16_to_cpu(udev->config[cfgno].desc. + srclen = le16_to_cpu(udev->config[cfgno].desc. wTotalLength); } if (off < srclen) { @@ -895,11 +889,66 @@ read_descriptors(struct file *filp, struct kobject *kobj, } return count - nleft; } +static BIN_ATTR_RO(descriptors, 18 + 65535); /* dev descr + max-size raw descriptor */ -static struct bin_attribute dev_bin_attr_descriptors = { - .attr = {.name = "descriptors", .mode = 0444}, - .read = read_descriptors, - .size = 18 + 65535, /* dev descr + max-size raw descriptor */ +static ssize_t +bos_descriptors_read(struct file *filp, struct kobject *kobj, + struct bin_attribute *attr, + char *buf, loff_t off, size_t count) +{ + struct device *dev = kobj_to_dev(kobj); + struct usb_device *udev = to_usb_device(dev); + struct usb_host_bos *bos = udev->bos; + struct usb_bos_descriptor *desc; + size_t desclen, n = 0; + + if (bos) { + desc = bos->desc; + desclen = le16_to_cpu(desc->wTotalLength); + if (off < desclen) { + n = min(count, desclen - (size_t) off); + memcpy(buf, (void *) desc + off, n); + } + } + return n; +} +static BIN_ATTR_RO(bos_descriptors, 65535); /* max-size BOS */ + +/* When modifying this list, be sure to modify dev_bin_attrs_are_visible() + * accordingly. + */ +static struct bin_attribute *dev_bin_attrs[] = { + &bin_attr_descriptors, + &bin_attr_bos_descriptors, + NULL +}; + +static umode_t dev_bin_attrs_are_visible(struct kobject *kobj, + struct bin_attribute *a, int n) +{ + struct device *dev = kobj_to_dev(kobj); + struct usb_device *udev = to_usb_device(dev); + + /* All USB devices have a device descriptor, so the descriptors + * attribute always exists. No need to check for its visibility. + */ + if (a == &bin_attr_bos_descriptors) { + if (udev->bos == NULL) + return 0; + } + return a->attr.mode; +} + +static const struct attribute_group dev_bin_attr_grp = { + .bin_attrs = dev_bin_attrs, + .is_bin_visible = dev_bin_attrs_are_visible, +}; + +const struct attribute_group *usb_device_groups[] = { + &dev_attr_grp, + &dev_string_attr_grp, + &dev_bin_attr_grp, + NULL }; /* @@ -1017,10 +1066,6 @@ int usb_create_sysfs_dev_files(struct usb_device *udev) struct device *dev = &udev->dev; int retval; - retval = device_create_bin_file(dev, &dev_bin_attr_descriptors); - if (retval) - goto error; - retval = add_persist_attributes(dev); if (retval) goto error; @@ -1050,7 +1095,6 @@ void usb_remove_sysfs_dev_files(struct usb_device *udev) remove_power_attributes(dev); remove_persist_attributes(dev); - device_remove_bin_file(dev, &dev_bin_attr_descriptors); } /* Interface Association Descriptor fields */