My apologies for any process mistakes in submitting this as it is my
first ever attempt at a Linux kernel patch.
I have a somewhat rough patch that introduces a modalias sysfs
attribute to kernel modules (both builtin and loaded). The goal of
this patch is to expose the driver matching values from the modalias
to inform policy decisions in userspace for devices with the
authorized attribute in sysfs. In other words with this patch tools
like USBGuard could leverage not only modules.aliases, but also the
aliases for the builtin modules to match devices with drivers before
deciding to authorize a device or not. This is particularly useful in
cases when new devices shouldn't be allowed part of the time like for
lock screens.
One other approach I considered was generating a builtin.alias file at
build time which would be installed alongside modules.alias. I have a
patch for this I could post as an alternative or in addition if it is
preferred.
I don't really like that it has to walk all drivers for all buses each
time the modalias attribute is read, but it shouldn't be that often
and I didn't see a better way of doing it though I am not familiar
with the kernel data structures available.
There are some flaws with this design in that some modaliases are not
associated with a bus. However, the only modules that really benefit
from this are ones with drivers associated with buses that make use of
the authorized attribute (USB, PCI, maybe others).
I only implemented USB for the proof-of-concept, but if this looks
like a viable option I could go back and implement PCI and any other
buses that use the authorized attribute.
Additionally, I haven't refactored files2alias to not have duplicate
code, but I am not sure how feasible that is given we would need to
share code between build-time userspace and the kernel. I did keep the
code limited to a single file so that it could possibly be compiled in
both environments, but type sizing of structs will be tricky for
cross-compilation.
Here is the patch:
>From fc8855454debb520a9d28031a825bc48852ccc1a Mon Sep 17 00:00:00 2001
From: Allen Webb <allenwebb@xxxxxxxxxx>
Date: Thu, 20 Oct 2022 19:53:04 +0000
Subject: [PATCH] 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.
BUG=chromium:1300574
TEST=cat /sys/modules/usb_storage/modalias
Change-Id: I83b6f0c30e06e65cbe223f1606187283fcb13215
Signed-off-by: Allen Webb <allenwebb@xxxxxxxxxx>
---
drivers/base/Makefile | 2 +-
drivers/base/base.h | 8 ++
drivers/base/bus.c | 42 ++++++
drivers/base/mod_devicetable.c | 243 +++++++++++++++++++++++++++++++++
drivers/usb/core/driver.c | 2 +
include/linux/device/bus.h | 8 ++
include/linux/module.h | 1 +
kernel/module/internal.h | 2 +
kernel/module/sysfs.c | 100 ++++++++++++++
kernel/params.c | 2 +
10 files changed, 409 insertions(+), 1 deletion(-)
create mode 100644 drivers/base/mod_devicetable.c
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 83217d243c25b..924d46ae987f4 100644
--- a/drivers/base/Makefile
+++ b/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/
diff --git a/drivers/base/base.h b/drivers/base/base.h
index b3a43a164dcd1..7ac5f7a547be8 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -175,6 +175,14 @@ 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
diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 7ca47e5b3c1f4..4e0c5925545e5 100644
--- a/drivers/base/bus.c
+++ b/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)
diff --git a/drivers/base/mod_devicetable.c b/drivers/base/mod_devicetable.c
new file mode 100644
index 0000000000000..0d98b3bf0d8d3
--- /dev/null
+++ b/drivers/base/mod_devicetable.c
@@ -0,0 +1,243 @@
+// 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;
+}
diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 7e7e119c253fb..fdbc197b64c9c 100644
--- a/drivers/usb/core/driver.c
+++ b/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,
};
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index d8b29ccd07e56..cce0bedec63d9 100644
--- a/include/linux/device/bus.h
+++ b/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,
diff --git a/include/linux/module.h b/include/linux/module.h
index 518296ea7f73a..68fe7bfc38683 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -48,6 +48,7 @@ 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 {
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 680d980a4fb29..63b794cd65df2 100644
--- a/kernel/module/internal.h
+++ b/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,
diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
index ce68f821dcd12..8696334dcaadc 100644
--- a/kernel/module/sysfs.c
+++ b/kernel/module/sysfs.c
@@ -5,6 +5,8 @@
* Copyright (C) 2008 Rusty Russell
*/
+#include <linux/device/bus.h>
+#include <linux/device/driver.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
@@ -240,6 +242,102 @@ static inline void add_notes_attrs(struct module
*mod, const struct load_info *i
static inline void remove_notes_attrs(struct module *mod) { }
#endif /* CONFIG_KALLSYMS */
+/* Track of the buffer and module identity in callbacks when walking
the list of
+ * drivers for each bus.
+ */
+struct modalias_bus_print_state {
+ struct module_kobject *mk;
+ char *buf;
+ size_t count;
+ ssize_t len;
+};
+
+static int print_modalias_for_drv(struct device_driver *drv, void *p)
+{
+ struct modalias_bus_print_state *s = p;
+ struct module_kobject *mk = s->mk;
+ ssize_t len;
+ /* Skip drivers that do not match this module. */
+ if (mk->mod) {
+ if (mk->mod != drv->owner)
+ return 0;
+ } else if (!mk->kobj.name || !drv->mod_name ||
+ strcmp(mk->kobj.name, drv->mod_name))
+ return 0;
+
+ if (drv->bus && drv->bus->drv_to_modalias) {
+ len = drv->bus->drv_to_modalias(drv, s->buf + s->len,
+ s->count - s->len);
+ if (len < 0)
+ return len;
+ s->len += len;
+ }
+
+ s->len += scnprintf(&s->buf[s->len], s->count - s->len, "driver %s\n",
+ drv->name);
+ return 0;
+}
+
+static int print_modalias_for_bus(struct bus_type *type, void *p)
+{
+ return bus_for_each_drv(type, NULL, p, print_modalias_for_drv);
+}
+
+static ssize_t module_modalias_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr,
+ char *buf, loff_t pos, size_t count)
+{
+ struct module_kobject *mk = container_of(kobj, struct module_kobject,
+ kobj);
+ struct modalias_bus_print_state state = {mk, buf, count, 0};
+ int error = 0;
+
+ if (pos != 0)
+ return -EINVAL;
+
+ error = bus_for_each(&state, print_modalias_for_bus);
+ if (error)
+ return error;
+
+ if (mk->mod)
+ state.len += scnprintf(&buf[state.len], count - state.len,
+ "modalias %s %s\n", kobject_name(kobj),
+ mk->mod->name);
+ else
+ state.len += scnprintf(&buf[state.len], count - state.len,
+ "modalias %s NULL\n",
+ kobject_name(kobj));
+
+ /*
+ * The caller checked the pos and count against our size.
+ */
+ return state.len;
+}
+
+/* Used in kernel/params.c for builtin modules.
+ *
+ * `struct module_kobject` is used instead of `struct module` because for
+ * builtin modules, the `struct module` is not available when this is called.
+ */
+void add_modalias_attr(struct module_kobject *mk)
+{
+ sysfs_bin_attr_init(&mk->modalias_attr);
+ mk->modalias_attr.attr.name = "modalias";
+ mk->modalias_attr.attr.mode = 0444;
+ mk->modalias_attr.read = module_modalias_read;
+ if (sysfs_create_bin_file(&mk->kobj, &mk->modalias_attr)) {
+ /* We shouldn't ignore the return type, but there is nothing to
+ * do.
+ */
+ return;
+ }
+}
+
+static void remove_modalias_attr(struct module_kobject *mk)
+{
+ sysfs_remove_bin_file(&mk->kobj, &mk->modalias_attr);
+}
+
static void del_usage_links(struct module *mod)
{
#ifdef CONFIG_MODULE_UNLOAD
@@ -398,6 +496,7 @@ int mod_sysfs_setup(struct module *mod,
add_sect_attrs(mod, info);
add_notes_attrs(mod, info);
+ add_modalias_attr(&mod->mkobj);
return 0;
@@ -415,6 +514,7 @@ int mod_sysfs_setup(struct module *mod,
static void mod_sysfs_fini(struct module *mod)
{
+ remove_modalias_attr(&mod->mkobj);
remove_notes_attrs(mod);
remove_sect_attrs(mod);
mod_kobject_put(mod);
diff --git a/kernel/params.c b/kernel/params.c
index 5b92310425c50..111024196361a 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -13,6 +13,7 @@
#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/security.h>
+#include "module/internal.h"
#ifdef CONFIG_SYSFS
/* Protects all built-in parameters, modules use their own param_lock */
@@ -815,6 +816,7 @@ static void __init kernel_add_sysfs_param(const char *name,
BUG_ON(err);
kobject_uevent(&mk->kobj, KOBJ_ADD);
kobject_put(&mk->kobj);
+ add_modalias_attr(mk);
}
/*
--
2.37.3
Allen
