modules: add modalias file to sysfs for modules.

USB devices support the authorized attribute which can be used by
user-space to implement trust-based systems for enabling USB devices. It
would be helpful when building these systems to be able to know in
advance which kernel drivers (or modules) are reachable from a
particular USB device.

This information is readily available for external modules in
modules.alias. However, builtin kernel modules are not covered. This
patch adds a sys-fs attribute to both builtin and loaded modules
exposing the matching rules in the modalias format for integration
with tools like USBGuard.

Signed-off-by: Allen Webb <allenwebb@google.com>

drivers/base/Makefile

@@ -15,7 +15,7 @@ obj-y				+= firmware_loader/
 obj-$(CONFIG_NUMA)	+= node.o
 obj-$(CONFIG_MEMORY_HOTPLUG) += memory.o
 ifeq ($(CONFIG_SYSFS),y)
-obj-$(CONFIG_MODULES)	+= module.o
+obj-$(CONFIG_MODULES)	+= mod_devicetable.o module.o
 endif
 obj-$(CONFIG_SYS_HYPERVISOR) += hypervisor.o
 obj-$(CONFIG_REGMAP)	+= regmap/

drivers/base/base.h

@@ -172,6 +172,14 @@ static inline void module_add_driver(struct module *mod,
 static inline void module_remove_driver(struct device_driver *drv) { }
 #endif
 
+#if defined(CONFIG_SYSFS)
+ssize_t usb_drv_to_modalias(struct device_driver *drv, char *buf,
+			    size_t count);
+#else
+static inline ssize_t usb_drv_to_modalias(struct device_driver *drv, char *buf,
+					  size_t count) { return -ENOSUP; }
+#endif
+
 #ifdef CONFIG_DEVTMPFS
 extern int devtmpfs_init(void);
 #else

drivers/base/bus.c

@@ -178,6 +178,48 @@ static const struct kset_uevent_ops bus_uevent_ops = {
 
 static struct kset *bus_kset;
 
+/**
+ * bus_for_each - bus iterator.
+ * @start: bus to start iterating from.
+ * @data: data for the callback.
+ * @fn: function to be called for each device.
+ *
+ * Iterate over list of buses, and call @fn for each,
+ * passing it @data. If @start is not NULL, we use that bus to
+ * begin iterating from.
+ *
+ * We check the return of @fn each time. If it returns anything
+ * other than 0, we break out and return that value.
+ *
+ * NOTE: The bus that returns a non-zero value is not retained
+ * in any way, nor is its refcount incremented. If the caller needs
+ * to retain this data, it should do so, and increment the reference
+ * count in the supplied callback.
+ */
+int bus_for_each(void *data, int (*fn)(struct bus_type *, void *))
+{
+	int error = 0;
+	struct bus_type *bus;
+	struct subsys_private *bus_prv;
+	struct kset *subsys;
+	struct kobject *k;
+
+	spin_lock(&bus_kset->list_lock);
+
+	list_for_each_entry(k, &bus_kset->list, entry) {
+		subsys = container_of(k, struct kset, kobj);
+		bus_prv = container_of(subsys, struct subsys_private, subsys);
+		bus = bus_prv->bus;
+		error = fn(bus, data);
+		if (error)
+			break;
+	}
+
+	spin_unlock(&bus_kset->list_lock);
+	return error;
+}
+EXPORT_SYMBOL_GPL(bus_for_each);
+
 /* Manually detach a device from its associated driver. */
 static ssize_t unbind_store(struct device_driver *drv, const char *buf,
 			    size_t count)

drivers/base/mod_devicetable.c

@@ -0,0 +1,241 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * mod_devicetable.c - helpers for displaying modaliases through sysfs.
+ *
+ * This borrows a lot from file2alias.c
+ */
+
+#include <linux/device/bus.h>
+#include <linux/device.h>
+#include <linux/usb.h>
+
+#include "../usb/core/usb.h"
+
+#define ADD(buf, count, len, sep, cond, field)				\
+do {									\
+	if (cond)							\
+		(len) += scnprintf(&(buf)[len],				\
+			(count) - (len),				\
+			sizeof(field) == 1 ? (sep "%02X") :		\
+			sizeof(field) == 2 ? (sep "%04X") :		\
+			sizeof(field) == 4 ? (sep "%08X") : "",		\
+			(field));					\
+	else								\
+		(len) += scnprintf(&(buf)[len], (count) - (len), (sep "*")); \
+} while (0)
+
+/* USB related modaliases can be split because of device number matching, so
+ * this function handles individual modaliases for one segment of the range.
+ *
+ *
+ */
+static ssize_t usb_id_to_modalias(const struct usb_device_id *id,
+				  unsigned int bcdDevice_initial,
+				  int bcdDevice_initial_digits,
+				  unsigned char range_lo,
+				  unsigned char range_hi,
+				  unsigned char max, const char *mod_name,
+				  char *buf, size_t count)
+{
+	ssize_t len = 0;
+
+	ADD(buf, count, len, "alias usb:v",
+	    id->match_flags & USB_DEVICE_ID_MATCH_VENDOR, id->idVendor);
+	ADD(buf, count, len, "p", id->match_flags & USB_DEVICE_ID_MATCH_PRODUCT,
+	    id->idProduct);
+
+	len += scnprintf(&buf[len], count - len, "d");
+	if (bcdDevice_initial_digits)
+		len += scnprintf(&buf[len], count - len, "%0*X",
+			bcdDevice_initial_digits, bcdDevice_initial);
+	if (range_lo == range_hi) {
+		len += scnprintf(&buf[len], count - len, "%X", range_lo);
+	} else if (range_lo > 0 || range_hi < max) {
+		if (range_lo > 0x9 || range_hi < 0xA) {
+			len += scnprintf(&buf[len], count - len, "[%X-%X]",
+					 range_lo, range_hi);
+		} else {
+			len += scnprintf(&buf[len], count - len,
+				range_lo < 0x9 ? "[%X-9" : "[%X",
+				range_lo);
+			len += scnprintf(&buf[len], count - len,
+				range_hi > 0xA ? "A-%X]" : "%X]",
+				range_hi);
+		}
+	}
+	if (bcdDevice_initial_digits < (sizeof(id->bcdDevice_lo) * 2 - 1))
+		len += scnprintf(&buf[len], count - len, "*");
+
+	ADD(buf, count, len, "dc",
+	    id->match_flags & USB_DEVICE_ID_MATCH_DEV_CLASS, id->bDeviceClass);
+	ADD(buf, count, len, "dsc",
+	    id->match_flags & USB_DEVICE_ID_MATCH_DEV_SUBCLASS,
+	    id->bDeviceSubClass);
+	ADD(buf, count, len, "dp",
+	    id->match_flags & USB_DEVICE_ID_MATCH_DEV_PROTOCOL,
+	    id->bDeviceProtocol);
+	ADD(buf, count, len, "ic",
+	    id->match_flags & USB_DEVICE_ID_MATCH_INT_CLASS,
+	    id->bInterfaceClass);
+	ADD(buf, count, len, "isc",
+	    id->match_flags & USB_DEVICE_ID_MATCH_INT_SUBCLASS,
+	    id->bInterfaceSubClass);
+	ADD(buf, count, len, "ip",
+	    id->match_flags & USB_DEVICE_ID_MATCH_INT_PROTOCOL,
+	    id->bInterfaceProtocol);
+	ADD(buf, count, len, "in",
+	    id->match_flags & USB_DEVICE_ID_MATCH_INT_NUMBER,
+	    id->bInterfaceNumber);
+
+	len += scnprintf(&buf[len], count - len, " %s\n", mod_name);
+	return len;
+}
+
+/* Handles increment/decrement of BCD formatted integers */
+/* Returns the previous value, so it works like i++ or i-- */
+static unsigned int incbcd(unsigned int *bcd,
+			   int inc,
+			   unsigned char max,
+			   size_t chars)
+{
+	unsigned int init = *bcd, i, j;
+	unsigned long long c, dec = 0;
+
+	/* If bcd is not in BCD format, just increment */
+	if (max > 0x9) {
+		*bcd += inc;
+		return init;
+	}
+
+	/* Convert BCD to Decimal */
+	for (i = 0 ; i < chars ; i++) {
+		c = (*bcd >> (i << 2)) & 0xf;
+		c = c > 9 ? 9 : c; /* force to bcd just in case */
+		for (j = 0 ; j < i ; j++)
+			c = c * 10;
+		dec += c;
+	}
+
+	/* Do our increment/decrement */
+	dec += inc;
+	*bcd  = 0;
+
+	/* Convert back to BCD */
+	for (i = 0 ; i < chars ; i++) {
+		for (c = 1, j = 0 ; j < i ; j++)
+			c = c * 10;
+		c = (dec / c) % 10;
+		*bcd += c << (i << 2);
+	}
+	return init;
+}
+
+/* Print the modaliases for the specified struct usb_device_id.
+ */
+static ssize_t usb_id_to_modalias_multi(const struct usb_device_id *id,
+					const char *mod_name, char *buf,
+					size_t count)
+{
+	ssize_t len = 0;
+	unsigned int devlo, devhi;
+	unsigned char chi, clo, max;
+	int ndigits;
+
+	devlo = id->match_flags & USB_DEVICE_ID_MATCH_DEV_LO ?
+		id->bcdDevice_lo : 0x0U;
+	devhi = id->match_flags & USB_DEVICE_ID_MATCH_DEV_HI ?
+		id->bcdDevice_hi : ~0x0U;
+
+	/* Figure out if this entry is in bcd or hex format */
+	max = 0x9; /* Default to decimal format */
+	for (ndigits = 0 ; ndigits < sizeof(id->bcdDevice_lo) * 2 ; ndigits++) {
+		clo = (devlo >> (ndigits << 2)) & 0xf;
+		chi = ((devhi > 0x9999 ? 0x9999 : devhi) >>
+		       (ndigits << 2)) & 0xf;
+		if (clo > max || chi > max) {
+			max = 0xf;
+			break;
+		}
+	}
+
+	/*
+	 * Some modules (visor) have empty slots as placeholder for
+	 * run-time specification that results in catch-all alias
+	 */
+	if (!(id->idVendor || id->idProduct || id->bDeviceClass ||
+	      id->bInterfaceClass))
+		return len;
+
+	/* Convert numeric bcdDevice range into fnmatch-able pattern(s) */
+	for (ndigits = sizeof(id->bcdDevice_lo) * 2 - 1; devlo <= devhi;
+	     ndigits--) {
+		clo = devlo & 0xf;
+		chi = devhi & 0xf;
+		/* If we are in bcd mode, truncate if necessary */
+		if (chi > max)
+			chi = max;
+		devlo >>= 4;
+		devhi >>= 4;
+
+		if (devlo == devhi || !ndigits) {
+			len += usb_id_to_modalias(id, devlo, ndigits, clo, chi,
+						  max, mod_name, buf + len,
+						  count - len);
+			break;
+		}
+
+		if (clo > 0x0)
+			len += usb_id_to_modalias(id,
+				incbcd(&devlo, 1, max,
+				       sizeof(id->bcdDevice_lo) * 2),
+				ndigits, clo, max, max, mod_name, buf + len,
+				count - len);
+
+		if (chi < max)
+			len += usb_id_to_modalias(id,
+				incbcd(&devhi, -1, max,
+				       sizeof(id->bcdDevice_lo) * 2),
+				ndigits, 0x0, chi, max, mod_name, buf + len,
+				count - len);
+	}
+	return len;
+}
+
+/* Print the modaliases for the given driver assumed to be an usb_driver or
+ * usb_device_driver.
+ *
+ * "alias" is prepended and the module name is appended to each modalias to
+ * match the format in modules.aliases.
+ *
+ * The modaliases will be written out to @buf with @count being the maximum
+ * bytes to write. The return value is a negative errno on error or the number
+ * of bytes written to @buf on success.
+ */
+ssize_t usb_drv_to_modalias(struct device_driver *drv, char *buf,
+			    size_t count)
+{
+	ssize_t len = 0;
+	const struct usb_device_id *id;
+	const char *mod_name;
+
+	if (drv->bus != &usb_bus_type)
+		return -EINVAL;
+
+	if (drv->owner)
+		mod_name = drv->owner->name;
+	else
+		mod_name = drv->mod_name;
+
+	if (is_usb_device_driver(drv))
+		id = to_usb_device_driver(drv)->id_table;
+	else
+		id = to_usb_driver(drv)->id_table;
+	if (!id)
+		return len;
+
+	for (; id->match_flags; id++) {
+		len += usb_id_to_modalias_multi(id, mod_name, buf + len,
+						count - len);
+	}
+	return len;
+}

drivers/usb/core/driver.c

@@ -32,6 +32,7 @@
 #include <linux/usb/quirks.h>
 #include <linux/usb/hcd.h>
 
+#include "../../base/base.h"
 #include "usb.h"
 
 
@@ -2030,4 +2031,5 @@ struct bus_type usb_bus_type = {
 	.match =	usb_device_match,
 	.uevent =	usb_uevent,
 	.need_parent_lock =	true,
+	.drv_to_modalias = usb_drv_to_modalias,
 };

include/linux/device/bus.h

@@ -61,6 +61,10 @@ struct fwnode_handle;
  *			this bus.
  * @dma_cleanup:	Called to cleanup DMA configuration on a device on
  *			this bus.
+ * @drv_to_modalias:    Called to convert the matching IDs in a
+ *                      struct device_driver to their corresponding modaliases.
+ *                      Note that the struct device_driver is expected to belong
+ *                      to this bus.
  * @pm:		Power management operations of this bus, callback the specific
  *		device driver's pm-ops.
  * @iommu_ops:  IOMMU specific operations for this bus, used to attach IOMMU
@@ -107,6 +111,9 @@ struct bus_type {
 	int (*dma_configure)(struct device *dev);
 	void (*dma_cleanup)(struct device *dev);
 
+	ssize_t (*drv_to_modalias)(struct device_driver *drv, char *buf,
+				   size_t count);
+
 	const struct dev_pm_ops *pm;
 
 	const struct iommu_ops *iommu_ops;
@@ -161,6 +168,7 @@ void subsys_dev_iter_init(struct subsys_dev_iter *iter,
 struct device *subsys_dev_iter_next(struct subsys_dev_iter *iter);
 void subsys_dev_iter_exit(struct subsys_dev_iter *iter);
 
+int bus_for_each(void *data, int (*fn)(struct bus_type *, void *));
 int bus_for_each_dev(struct bus_type *bus, struct device *start, void *data,
 		     int (*fn)(struct device *dev, void *data));
 struct device *bus_find_device(struct bus_type *bus, struct device *start,

include/linux/module.h

@@ -47,6 +47,7 @@ struct module_kobject {
 	struct kobject *drivers_dir;
 	struct module_param_attrs *mp;
 	struct completion *kobj_completion;
+	struct bin_attribute modalias_attr;
 } __randomize_layout;
 
 struct module_attribute {

kernel/module/internal.h

@@ -259,11 +259,13 @@ static inline void add_kallsyms(struct module *mod, const struct load_info *info
 #endif /* CONFIG_KALLSYMS */
 
 #ifdef CONFIG_SYSFS
+void add_modalias_attr(struct module_kobject *mk);
 int mod_sysfs_setup(struct module *mod, const struct load_info *info,
 		    struct kernel_param *kparam, unsigned int num_params);
 void mod_sysfs_teardown(struct module *mod);
 void init_param_lock(struct module *mod);
 #else /* !CONFIG_SYSFS */
+static inline void add_modalias_attr(struct module_kobject *mk) {}
 static inline int mod_sysfs_setup(struct module *mod,
 			   	  const struct load_info *info,
 			   	  struct kernel_param *kparam,