[PATCH] driver core: enforce device_lock for driver_match_device()

[PATCH] driver core: enforce device_lock for driver_match_device()

[Runyu Xiao]

Currently driver_match_device() is called from three sites. The
__device_attach_driver() path already runs under device_lock(dev), but
bind_store() and __driver_attach() can still enter bus match()
callbacks without that lock held.

That inconsistency leaves bus-private driver_override readers exposed.
Several buses still read private driver_override strings from their
match callbacks while the write side relies on driver_set_override()
under device_lock(dev). If bind_store() or __driver_attach() reaches
such a match callback without that lock, it can race with
driver_override replacement and old-string free.

This issue was first flagged by our static analysis tool while auditing
driver_override match paths, then manually confirmed on Linux v6.18.21.
We reproduced the race with no-device KCSAN/MSV harnesses across AMBA,
WMI, RPMSG, VMBUS, VDPA, CDX, CSS, FSL-MC, and PCI. Those reports all
reduce to the same core-side gap in driver_match_device().

Fix this by introducing driver_match_device_locked(), which guarantees
holding device_lock(dev) with a scoped guard before entering the bus
match callback. Convert the two unlocked call sites to this helper, and
add a device_lock_assert() to driver_match_device() so the contract is
explicit.

This matches the locking requirement already assumed by
driver_set_override()-based driver_override implementations and avoids
trying to paper over the problem in each individual bus match()
callback, where taking device_lock(dev) locally would conflict with
already-locked callers.

Build-tested with:
  make olddefconfig
  make -j"$(nproc)" drivers/base/bus.o drivers/base/dd.o

Fixes: 49b420a13ff9 ("driver core: check bus->match without holding device lock")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
 drivers/base/base.h | 10 ++++++++++
 drivers/base/bus.c  |  2 +-
 drivers/base/dd.c   |  2 +-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 86fa7fbb3548..4ec487e34d1a 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -166,9 +166,19 @@ void device_set_deferred_probe_reason(const struct device *dev, struct va_format
 static inline int driver_match_device(const struct device_driver *drv,
 				      struct device *dev)
 {
+	device_lock_assert(dev);
+
 	return drv->bus->match ? drv->bus->match(dev, drv) : 1;
 }
 
+static inline int driver_match_device_locked(const struct device_driver *drv,
+					     struct device *dev)
+{
+	guard(device)(dev);
+
+	return driver_match_device(drv, dev);
+}
+
 static inline void dev_sync_state(struct device *dev)
 {
 	if (dev->bus->sync_state)
diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 2653670f962f..2b039aa2da74 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -263,7 +263,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
 	int err = -ENODEV;
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
-	if (dev && driver_match_device(drv, dev)) {
+	if (dev && driver_match_device_locked(drv, dev)) {
 		err = device_driver_attach(drv, dev);
 		if (!err) {
 			/* success */
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 2996f4c667c4..30c3e55ff5ff 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1230,7 +1230,7 @@ static int __driver_attach(struct device *dev, void *data)
 	 * is an error.
 	 */
 
-	ret = driver_match_device(drv, dev);
+	ret = driver_match_device_locked(drv, dev);
 	if (ret == 0) {
 		/* no match */
 		return 0;
-- 
2.34.1

Re: [PATCH] driver core: enforce device_lock for driver_match_device()

[Greg KH]

On Wed, Jun 03, 2026 at 12:08:29AM +0800, Runyu Xiao wrote:
> Currently driver_match_device() is called from three sites. The
> __device_attach_driver() path already runs under device_lock(dev), but
> bind_store() and __driver_attach() can still enter bus match()
> callbacks without that lock held.
> 
> That inconsistency leaves bus-private driver_override readers exposed.
> Several buses still read private driver_override strings from their
> match callbacks while the write side relies on driver_set_override()
> under device_lock(dev). If bind_store() or __driver_attach() reaches
> such a match callback without that lock, it can race with
> driver_override replacement and old-string free.
> 
> This issue was first flagged by our static analysis tool while auditing
> driver_override match paths, then manually confirmed on Linux v6.18.21.

That is very old, please test on the latest 7.1-rc release as things
have changed in this area recently.

thanks,

greg k-h

Re: [PATCH] driver core: enforce device_lock for driver_match_device()

[Danilo Krummrich]

On Tue Jun 2, 2026 at 6:08 PM CEST, Runyu Xiao wrote:
> This issue was first flagged by our static analysis tool while auditing
> driver_override match paths, then manually confirmed on Linux v6.18.21.
> We reproduced the race with no-device KCSAN/MSV harnesses across AMBA,
> WMI, RPMSG, VMBUS, VDPA, CDX, CSS, FSL-MC, and PCI. Those reports all
> reduce to the same core-side gap in driver_match_device().

This is all fixed in driver-core-next already, please also see [1] and [2].

> Fix this by introducing driver_match_device_locked(), which guarantees
> holding device_lock(dev) with a scoped guard before entering the bus
> match callback. Convert the two unlocked call sites to this helper, and
> add a device_lock_assert() to driver_match_device() so the contract is
> explicit.

This approach was reverted [3] for the reasons documented in the linked patch.

Thanks,
Danilo

[1] https://lore.kernel.org/driver-core/20260303115720.48783-1-dakr@kernel.org/
[2] https://lore.kernel.org/driver-core/20260324005919.2408620-1-dakr@kernel.org/
[3] https://lore.kernel.org/driver-core/20260302002545.19389-1-dakr@kernel.org/

Re: [PATCH] driver core: enforce device_lock for driver_match_device()

[Runyu Xiao]

Hi Danilo, Greg,

Thanks for the pointers.

Understood. Since this is already being addressed in driver-core-next
through the generic driver_override infrastructure, and the
device_lock(driver_match_device()) approach was reverted for the reasons
you pointed out, I will not resend this patch.

I will retest the original issue on the latest tree and only follow up
again if there is still a remaining problem with the current
driver_override infrastructure.

Thanks,
Runyu

[PATCH v2 0/4] Convert remaining buses to generic driver_override handling

[Runyu Xiao]

This series converts four remaining buses from bus-private
driver_override handling to the generic driver-core infrastructure:

  - AMBA
  - RPMSG
  - VMBUS
  - CDX

These buses still keep private driver_override storage and read it
directly from their match paths. However, bus match() callbacks can be
reached from __driver_attach() without the device lock held, so those
raw reads can race with updates that replace and free the override
string.

The driver core already provides generic driver_override storage and
matching helpers with the required internal locking. Other buses have
already been converted to that model. This series switches the
remaining users above to the same infrastructure by:

  - removing bus-private driver_override storage
  - dropping bus-local driver_override sysfs handling
  - enabling struct bus_type.driver_override
  - using device_match_driver_override() in match paths

Bus-specific behavior is preserved where needed:

  - VMBUS keeps its dummy-id fallback for override-based binding
  - CDX keeps its override_only matching semantics
  - RPMSG converts its in-kernel override registration path to
    device_set_driver_override() and drops the old transport-local
    frees of bus-private override storage

Before preparing this v2 series, I rechecked the affected source paths
against v7.1-rc6. I also reran the existing report-specific no-device
KCSAN stand-ins on a local v7.1-rc6 guest for all four buses. Those
reruns again produced target-stack reports for the corresponding
driver_override update/match paths.

That runtime validation is still stand-in based rather than direct
hardware execution, but it reuses the real driver_set_override() helper
from the running v7.1-rc6 guest kernel and preserves the relevant
patch-local reader/writer contracts and caller chains.

Since v1:
  - reworked the series around the generic driver_override
    infrastructure instead of trying to serialize bus match() with
    device_lock(dev)
  - split the changes by bus
  - preserved VMBUS dummy-id fallback behavior explicitly
  - preserved CDX override_only matching semantics explicitly
  - converted the RPMSG in-kernel override registration path to the
    core helper
  - reran the four report-specific no-device KCSAN stand-ins on a
    local v7.1-rc6 guest and refreshed the validation basis
  - refreshed the commit messages accordingly

Runyu Xiao (4):
  amba: use generic driver_override infrastructure
  rpmsg: core: use generic driver_override infrastructure
  vmbus: use generic driver_override infrastructure
  cdx: use generic driver_override infrastructure

 drivers/amba/bus.c               | 35 +++++--------------------------
 drivers/cdx/cdx.c                | 40 +++++-------------------------------
 drivers/hv/vmbus_drv.c           | 36 +++++---------------------------
 drivers/rpmsg/qcom_glink_native.c |  2 --
 drivers/rpmsg/rpmsg_core.c       | 41 ++++++-------------------------------
 drivers/rpmsg/virtio_rpmsg_bus.c |  1 -
 include/linux/amba/bus.h         |  5 -----
 include/linux/cdx/cdx_bus.h      |  1 -
 include/linux/hyperv.h           |  6 ------
 include/linux/rpmsg.h            |  4 ----
 10 files changed, 21 insertions(+), 150 deletions(-)

-- 
2.34.1

[PATCH v2 1/4] amba: use generic driver_override infrastructure

[Runyu Xiao]

AMBA devices still keep driver_override in bus-private storage.

The sysfs write side updates that string through driver_set_override(),
which replaces the pointer and frees the old value. However,
driver_match_device() can call amba_match() from __driver_attach()
without holding the device lock, and amba_match() still dereferences
that private pointer directly.

That means a bind/unbind or reprobe path can race with a concurrent
driver_override update and make amba_match() compare against freed
memory.

Fix this by switching AMBA to the driver-core driver_override
infrastructure. This lets the core own the sysfs attribute and storage,
and uses device_match_driver_override() for the locked read in the match
path.

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/
Fixes: 3cf385713460 ("ARM: 8256/1: driver coamba: add device binding path 'driver_override'")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
drivers/amba/bus.c       | 35 +++++------------------------------
include/linux/amba/bus.h |  5 -----
 2 files changed, 5 insertions(+), 35 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 6d479caf89cb..df8333f90906 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -82,33 +82,6 @@ static void amba_put_disable_pclk(struct amba_device *pcdev)
 }
 
 
-static ssize_t driver_override_show(struct device *_dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct amba_device *dev = to_amba_device(_dev);
-	ssize_t len;
-
-	device_lock(_dev);
-	len = sprintf(buf, "%s\n", dev->driver_override);
-	device_unlock(_dev);
-	return len;
-}
-
-static ssize_t driver_override_store(struct device *_dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct amba_device *dev = to_amba_device(_dev);
-	int ret;
-
-	ret = driver_set_override(_dev, &dev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 #define amba_attr_func(name,fmt,arg...)					\
 static ssize_t name##_show(struct device *_dev,				\
 			   struct device_attribute *attr, char *buf)	\
@@ -126,7 +99,6 @@ amba_attr_func(resource, "\t%016llx\t%016llx\t%016lx\n",
 static struct attribute *amba_dev_attrs[] = {
 	&dev_attr_id.attr,
 	&dev_attr_resource.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(amba_dev);
@@ -209,6 +181,7 @@ static int amba_match(struct device *dev, const struct device_driver *drv)
 {
 	struct amba_device *pcdev = to_amba_device(dev);
 	const struct amba_driver *pcdrv = to_amba_driver(drv);
+	int ret;
 
 	mutex_lock(&pcdev->periphid_lock);
 	if (!pcdev->periphid) {
@@ -230,8 +203,9 @@ static int amba_match(struct device *dev, const struct device_driver *drv)
 	mutex_unlock(&pcdev->periphid_lock);
 
 	/* When driver_override is set, only bind to the matching driver */
-	if (pcdev->driver_override)
-		return !strcmp(pcdev->driver_override, drv->name);
+	ret = device_match_driver_override(dev, drv);
+	if (ret >= 0)
+		return ret;
 
 	return amba_lookup(pcdrv->id_table, pcdev) != NULL;
 }
@@ -435,6 +409,7 @@ static const struct dev_pm_ops amba_pm = {
  */
 const struct bus_type amba_bustype = {
 	.name		= "amba",
+	.driver_override = true,
 	.dev_groups	= amba_dev_groups,
 	.match		= amba_match,
 	.uevent		= amba_uevent,
diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index 9946276aff73..6c54d5c0d21f 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -71,11 +71,6 @@ struct amba_device {
 	unsigned int		cid;
 	struct amba_cs_uci_id	uci;
 	unsigned int		irq[AMBA_NR_IRQS];
-	/*
-	 * Driver name to force a match.  Do not set directly, because core
-	 * frees it.  Use driver_set_override() to set or clear it.
-	 */
-	const char		*driver_override;
 };
 
 struct amba_driver {
-- 
2.34.1

[PATCH v2 2/4] rpmsg: core: use generic driver_override infrastructure

[Runyu Xiao]

RPMSG still keeps driver_override in bus-private storage.

That private pointer can be updated from the sysfs driver_override
attribute, and also from rpmsg_register_device_override(). Both paths
replace the pointer and can free the old value.

However, driver_match_device() can call rpmsg_dev_match() from
__driver_attach() without holding the device lock, and rpmsg_dev_match()
still dereferences that private pointer directly.

This leaves the match path racing with concurrent driver_override
updates, with the usual risk of comparing against freed memory.

Switch rpmsg to the driver-core driver_override infrastructure. This
removes the private storage, uses device_match_driver_override() for the
locked read in rpmsg_dev_match(), and converts
rpmsg_register_device_override() to device_set_driver_override() so the
in-kernel override path uses the same core-managed storage. With that
storage now owned by struct device, drop the remaining rpmsg transport
release-path frees of rpdev->driver_override as well.

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/
Fixes: 39e47767ec9b ("rpmsg: Add driver_override device attribute for rpmsg_device")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
drivers/rpmsg/qcom_glink_native.c |  2 --
drivers/rpmsg/rpmsg_core.c        | 41 ++++++--------------------------------
drivers/rpmsg/virtio_rpmsg_bus.c  |  1 -
include/linux/rpmsg.h             |  4 ----
 4 files changed, 6 insertions(+), 42 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
index e7f7831d37f8..11d3007db5cd 100644
--- a/drivers/rpmsg/rpmsg_core.c
+++ b/drivers/rpmsg/rpmsg_core.c
@@ -358,33 +358,6 @@ rpmsg_show_attr(src, src, "0x%x\n");
 rpmsg_show_attr(dst, dst, "0x%x\n");
 rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
-	int ret;
-
-	ret = driver_set_override(dev, &rpdev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", rpdev->driver_override);
-	device_unlock(dev);
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 static ssize_t modalias_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
@@ -405,7 +378,6 @@ static struct attribute *rpmsg_dev_attrs[] = {
 	&dev_attr_dst.attr,
 	&dev_attr_src.attr,
 	&dev_attr_announce.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(rpmsg_dev);
@@ -424,9 +396,11 @@ static int rpmsg_dev_match(struct device *dev, const struct device_driver *drv)
 	const struct rpmsg_driver *rpdrv = to_rpmsg_driver(drv);
 	const struct rpmsg_device_id *ids = rpdrv->id_table;
 	unsigned int i;
+	int ret;
 
-	if (rpdev->driver_override)
-		return !strcmp(rpdev->driver_override, drv->name);
+	ret = device_match_driver_override(dev, drv);
+	if (ret >= 0)
+		return ret;
 
 	if (ids)
 		for (i = 0; ids[i].name[0]; i++)
@@ -533,6 +507,7 @@ static void rpmsg_dev_remove(struct device *dev)
 
 static const struct bus_type rpmsg_bus = {
 	.name		= "rpmsg",
+	.driver_override = true,
 	.match		= rpmsg_dev_match,
 	.dev_groups	= rpmsg_dev_groups,
 	.uevent		= rpmsg_uevent,
@@ -560,9 +535,7 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
 
 	device_initialize(dev);
 	if (driver_override) {
-		ret = driver_set_override(dev, &rpdev->driver_override,
-					  driver_override,
-					  strlen(driver_override));
+		ret = device_set_driver_override(dev, driver_override);
 		if (ret) {
 			dev_err(dev, "device_set_override failed: %d\n", ret);
 			put_device(dev);
@@ -573,8 +546,6 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
 	ret = device_add(dev);
 	if (ret) {
 		dev_err(dev, "device_add failed: %d\n", ret);
-		kfree(rpdev->driver_override);
-		rpdev->driver_override = NULL;
 		put_device(dev);
 	}
 
diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
index 401a4ece0c97..d9d4468e4cbd 100644
--- a/drivers/rpmsg/qcom_glink_native.c
+++ b/drivers/rpmsg/qcom_glink_native.c
@@ -1626,7 +1626,6 @@ static void qcom_glink_rpdev_release(struct device *dev)
 {
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
 
-	kfree(rpdev->driver_override);
 	kfree(rpdev);
 }
 
@@ -1862,7 +1861,6 @@ static void qcom_glink_device_release(struct device *dev)
 
 	/* Release qcom_glink_alloc_channel() reference */
 	kref_put(&channel->refcount, qcom_glink_channel_release);
-	kfree(rpdev->driver_override);
 	kfree(rpdev);
 }
 
diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
index 5ae15111fb4f..1b8bb05924af 100644
--- a/drivers/rpmsg/virtio_rpmsg_bus.c
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -374,7 +374,6 @@ static void virtio_rpmsg_release_device(struct device *dev)
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
 	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
 
-	kfree(rpdev->driver_override);
 	kfree(vch);
 }
 
diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
index 83266ce14642..2e40eb54155e 100644
--- a/include/linux/rpmsg.h
+++ b/include/linux/rpmsg.h
@@ -41,9 +41,6 @@ struct rpmsg_channel_info {
  * rpmsg_device - device that belong to the rpmsg bus
  * @dev: the device struct
  * @id: device id (used to match between rpmsg drivers and devices)
- * @driver_override: driver name to force a match; do not set directly,
- *                   because core frees it; use driver_set_override() to
- *                   set or clear it.
  * @src: local address
  * @dst: destination address
  * @ept: the rpmsg endpoint of this channel
@@ -53,7 +50,6 @@ struct rpmsg_channel_info {
 struct rpmsg_device {
 	struct device dev;
 	struct rpmsg_device_id id;
-	const char *driver_override;
 	u32 src;
 	u32 dst;
 	struct rpmsg_endpoint *ept;
-- 
2.34.1

Re: [PATCH v2 2/4] rpmsg: core: use generic driver_override infrastructure

[Mathieu Poirier]

On Wed, 3 Jun 2026 at 21:52, Runyu Xiao <runyu.xiao@seu.edu.cn> wrote:
>
> RPMSG still keeps driver_override in bus-private storage.
>
> That private pointer can be updated from the sysfs driver_override
> attribute, and also from rpmsg_register_device_override(). Both paths
> replace the pointer and can free the old value.
>
> However, driver_match_device() can call rpmsg_dev_match() from
> __driver_attach() without holding the device lock, and rpmsg_dev_match()
> still dereferences that private pointer directly.
>
> This leaves the match path racing with concurrent driver_override
> updates, with the usual risk of comparing against freed memory.
>
> Switch rpmsg to the driver-core driver_override infrastructure. This
> removes the private storage, uses device_match_driver_override() for the
> locked read in rpmsg_dev_match(), and converts
> rpmsg_register_device_override() to device_set_driver_override() so the
> in-kernel override path uses the same core-managed storage. With that
> storage now owned by struct device, drop the remaining rpmsg transport
> release-path frees of rpdev->driver_override as well.
>
> Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/
> Fixes: 39e47767ec9b ("rpmsg: Add driver_override device attribute for rpmsg_device")
> Cc: stable@vger.kernel.org
> Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
> ---
> drivers/rpmsg/qcom_glink_native.c |  2 --
> drivers/rpmsg/rpmsg_core.c        | 41 ++++++--------------------------------
> drivers/rpmsg/virtio_rpmsg_bus.c  |  1 -
> include/linux/rpmsg.h             |  4 ----

For the bottom 3:

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

>  4 files changed, 6 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index e7f7831d37f8..11d3007db5cd 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -358,33 +358,6 @@ rpmsg_show_attr(src, src, "0x%x\n");
>  rpmsg_show_attr(dst, dst, "0x%x\n");
>  rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
>
> -static ssize_t driver_override_store(struct device *dev,
> -                                    struct device_attribute *attr,
> -                                    const char *buf, size_t count)
> -{
> -       struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> -       int ret;
> -
> -       ret = driver_set_override(dev, &rpdev->driver_override, buf, count);
> -       if (ret)
> -               return ret;
> -
> -       return count;
> -}
> -
> -static ssize_t driver_override_show(struct device *dev,
> -                                   struct device_attribute *attr, char *buf)
> -{
> -       struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> -       ssize_t len;
> -
> -       device_lock(dev);
> -       len = sysfs_emit(buf, "%s\n", rpdev->driver_override);
> -       device_unlock(dev);
> -       return len;
> -}
> -static DEVICE_ATTR_RW(driver_override);
> -
>  static ssize_t modalias_show(struct device *dev,
>                              struct device_attribute *attr, char *buf)
>  {
> @@ -405,7 +378,6 @@ static struct attribute *rpmsg_dev_attrs[] = {
>         &dev_attr_dst.attr,
>         &dev_attr_src.attr,
>         &dev_attr_announce.attr,
> -       &dev_attr_driver_override.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(rpmsg_dev);
> @@ -424,9 +396,11 @@ static int rpmsg_dev_match(struct device *dev, const struct device_driver *drv)
>         const struct rpmsg_driver *rpdrv = to_rpmsg_driver(drv);
>         const struct rpmsg_device_id *ids = rpdrv->id_table;
>         unsigned int i;
> +       int ret;
>
> -       if (rpdev->driver_override)
> -               return !strcmp(rpdev->driver_override, drv->name);
> +       ret = device_match_driver_override(dev, drv);
> +       if (ret >= 0)
> +               return ret;
>
>         if (ids)
>                 for (i = 0; ids[i].name[0]; i++)
> @@ -533,6 +507,7 @@ static void rpmsg_dev_remove(struct device *dev)
>
>  static const struct bus_type rpmsg_bus = {
>         .name           = "rpmsg",
> +       .driver_override = true,
>         .match          = rpmsg_dev_match,
>         .dev_groups     = rpmsg_dev_groups,
>         .uevent         = rpmsg_uevent,
> @@ -560,9 +535,7 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
>
>         device_initialize(dev);
>         if (driver_override) {
> -               ret = driver_set_override(dev, &rpdev->driver_override,
> -                                         driver_override,
> -                                         strlen(driver_override));
> +               ret = device_set_driver_override(dev, driver_override);
>                 if (ret) {
>                         dev_err(dev, "device_set_override failed: %d\n", ret);
>                         put_device(dev);
> @@ -573,8 +546,6 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
>         ret = device_add(dev);
>         if (ret) {
>                 dev_err(dev, "device_add failed: %d\n", ret);
> -               kfree(rpdev->driver_override);
> -               rpdev->driver_override = NULL;
>                 put_device(dev);
>         }
>
> diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
> index 401a4ece0c97..d9d4468e4cbd 100644
> --- a/drivers/rpmsg/qcom_glink_native.c
> +++ b/drivers/rpmsg/qcom_glink_native.c
> @@ -1626,7 +1626,6 @@ static void qcom_glink_rpdev_release(struct device *dev)
>  {
>         struct rpmsg_device *rpdev = to_rpmsg_device(dev);
>
> -       kfree(rpdev->driver_override);
>         kfree(rpdev);
>  }
>
> @@ -1862,7 +1861,6 @@ static void qcom_glink_device_release(struct device *dev)
>
>         /* Release qcom_glink_alloc_channel() reference */
>         kref_put(&channel->refcount, qcom_glink_channel_release);
> -       kfree(rpdev->driver_override);
>         kfree(rpdev);
>  }
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 5ae15111fb4f..1b8bb05924af 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -374,7 +374,6 @@ static void virtio_rpmsg_release_device(struct device *dev)
>         struct rpmsg_device *rpdev = to_rpmsg_device(dev);
>         struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
>
> -       kfree(rpdev->driver_override);
>         kfree(vch);
>  }
>
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 83266ce14642..2e40eb54155e 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -41,9 +41,6 @@ struct rpmsg_channel_info {
>   * rpmsg_device - device that belong to the rpmsg bus
>   * @dev: the device struct
>   * @id: device id (used to match between rpmsg drivers and devices)
> - * @driver_override: driver name to force a match; do not set directly,
> - *                   because core frees it; use driver_set_override() to
> - *                   set or clear it.
>   * @src: local address
>   * @dst: destination address
>   * @ept: the rpmsg endpoint of this channel
> @@ -53,7 +50,6 @@ struct rpmsg_channel_info {
>  struct rpmsg_device {
>         struct device dev;
>         struct rpmsg_device_id id;
> -       const char *driver_override;
>         u32 src;
>         u32 dst;
>         struct rpmsg_endpoint *ept;
> --
> 2.34.1

[PATCH v2 3/4] vmbus: use generic driver_override infrastructure

[Runyu Xiao]

VMBUS devices still keep driver_override in bus-private storage.

The sysfs write side updates that string through driver_set_override(),
which replaces the pointer and frees the old value. However,
driver_match_device() can call into hv_vmbus_get_id() from
__driver_attach() without holding the device lock, and hv_vmbus_get_id()
still dereferences that private pointer directly.

That means a bind/reprobe path can race with a concurrent
driver_override update and make the match logic inspect freed memory.

Switch vmbus to the driver-core driver_override infrastructure. This
removes the private driver_override storage and uses
device_match_driver_override() for the locked read in the match path.

Keep the existing vmbus semantics intact: if driver_override matches but
no dynamic or static device ID matches, continue to return the dummy
vmbus_device_null ID so override-only binding still works as before.

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/
Fixes: d765edbb301c ("vmbus: add driver_override support")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
drivers/hv/vmbus_drv.c | 36 +++++-------------------------------
include/linux/hyperv.h |  6 ------
 2 files changed, 5 insertions(+), 37 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index d28ff45d4cfd..a81e2b097636 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -538,34 +538,6 @@ static ssize_t device_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(device);
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct hv_device *hv_dev = device_to_hv_device(dev);
-	int ret;
-
-	ret = driver_set_override(dev, &hv_dev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct hv_device *hv_dev = device_to_hv_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", hv_dev->driver_override);
-	device_unlock(dev);
-
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 /* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
 static struct attribute *vmbus_dev_attrs[] = {
 	&dev_attr_id.attr,
@@ -596,7 +568,6 @@ static struct attribute *vmbus_dev_attrs[] = {
 	&dev_attr_channel_vp_mapping.attr,
 	&dev_attr_vendor.attr,
 	&dev_attr_device.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -708,9 +679,11 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
 {
 	const guid_t *guid = &dev->dev_type;
 	const struct hv_vmbus_device_id *id;
+	int ret;
 
 	/* When driver_override is set, only bind to the matching driver */
-	if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+	ret = device_match_driver_override(&dev->device, &drv->driver);
+	if (ret == 0)
 		return NULL;
 
 	/* Look at the dynamic ids first, before the static ones */
@@ -719,7 +692,7 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(const struct hv_driver *
 		id = hv_vmbus_dev_match(drv->id_table, guid);
 
 	/* driver_override will always match, send a dummy id */
-	if (!id && dev->driver_override)
+	if (!id && ret > 0)
 		id = &vmbus_device_null;
 
 	return id;
@@ -1021,6 +994,7 @@ static const struct dev_pm_ops vmbus_pm = {
 /* The one and only one */
 static const struct bus_type  hv_bus = {
 	.name =		"vmbus",
+	.driver_override = true,
 	.match =		vmbus_match,
 	.shutdown =		vmbus_shutdown,
 	.remove =		vmbus_remove,
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 964f1be8150c..f9ede569602d 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1272,12 +1272,6 @@ struct hv_device {
 	u16 device_id;
 
 	struct device device;
-	/*
-	 * Driver name to force a match.  Do not set directly, because core
-	 * frees it.  Use driver_set_override() to set or clear it.
-	 */
-	const char *driver_override;
-
 	struct vmbus_channel *channel;
 	struct kset	     *channels_kset;
 	struct device_dma_parameters dma_parms;
-- 
2.34.1

[PATCH v2 4/4] cdx: use generic driver_override infrastructure

[Runyu Xiao]

CDX devices still keep driver_override in bus-private storage.

The sysfs write side updates that string through driver_set_override(),
which replaces the pointer and frees the old value. However,
driver_match_device() can call cdx_bus_match() from __driver_attach()
without holding the device lock, and cdx_bus_match() still dereferences
that private pointer directly.

That means the CDX match path can race with a concurrent
driver_override update and compare against freed memory.

Switch CDX to the driver-core driver_override infrastructure. This
removes the private driver_override storage, lets the core provide the
sysfs attribute, and uses device_match_driver_override() for the locked
read in cdx_bus_match().

Preserve the existing CDX override_only semantics: entries marked
override_only still require a matching driver_override, but ordinary ID
matches continue to work unchanged.

Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@kernel.org/
Fixes: 48a6c7bced2a ("cdx: add device attributes")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
drivers/cdx/cdx.c           | 40 +++++--------------------------------
include/linux/cdx/cdx_bus.h |  1 -
 2 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
index 9196dc50a48d..d3d230247262 100644
--- a/drivers/cdx/cdx.c
+++ b/drivers/cdx/cdx.c
@@ -156,8 +156,6 @@ static int cdx_unregister_device(struct device *dev,
 	} else {
 		cdx_destroy_res_attr(cdx_dev, MAX_CDX_DEV_RESOURCES);
 		debugfs_remove_recursive(cdx_dev->debugfs_dir);
-		kfree(cdx_dev->driver_override);
-		cdx_dev->driver_override = NULL;
 	}
 
 	/*
@@ -268,6 +266,7 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 	const struct cdx_driver *cdx_drv = to_cdx_driver(drv);
 	const struct cdx_device_id *found_id = NULL;
 	const struct cdx_device_id *ids;
+	int ret;
 
 	if (cdx_dev->is_bus)
 		return false;
@@ -275,7 +274,8 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 	ids = cdx_drv->match_id_table;
 
 	/* When driver_override is set, only bind to the matching driver */
-	if (cdx_dev->driver_override && strcmp(cdx_dev->driver_override, drv->name))
+	ret = device_match_driver_override(dev, drv);
+	if (ret == 0)
 		return false;
 
 	found_id = cdx_match_id(ids, cdx_dev);
@@ -289,7 +289,7 @@ static int cdx_bus_match(struct device *dev, const struct device_driver *drv)
 		 */
 		if (!found_id->override_only)
 			return true;
-		if (cdx_dev->driver_override)
+		if (ret > 0)
 			return true;
 
 		ids = found_id + 1;
@@ -453,36 +453,6 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(modalias);
 
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct cdx_device *cdx_dev = to_cdx_device(dev);
-	int ret;
-
-	if (WARN_ON(dev->bus != &cdx_bus_type))
-		return -EINVAL;
-
-	ret = driver_set_override(dev, &cdx_dev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct cdx_device *cdx_dev = to_cdx_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", cdx_dev->driver_override);
-	device_unlock(dev);
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
-
 static ssize_t enable_store(struct device *dev, struct device_attribute *attr,
 			    const char *buf, size_t count)
 {
@@ -552,7 +522,6 @@ static struct attribute *cdx_dev_attrs[] = {
 	&dev_attr_class.attr,
 	&dev_attr_revision.attr,
 	&dev_attr_modalias.attr,
-	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -646,6 +615,7 @@ ATTRIBUTE_GROUPS(cdx_bus);
 
 const struct bus_type cdx_bus_type = {
 	.name		= "cdx",
+	.driver_override = true,
 	.match		= cdx_bus_match,
 	.probe		= cdx_probe,
 	.remove		= cdx_remove,
diff --git a/include/linux/cdx/cdx_bus.h b/include/linux/cdx/cdx_bus.h
index b1ba97f6c9ad..f1a107b232da 100644
--- a/include/linux/cdx/cdx_bus.h
+++ b/include/linux/cdx/cdx_bus.h
@@ -165,7 +165,6 @@ struct cdx_device {
 	bool enabled;
 	u32 msi_dev_id;
 	u32 num_msi;
-	const char *driver_override;
 	struct mutex irqchip_lock;
 	bool msi_write_pending;
 };
-- 
2.34.1

Re: [PATCH v2 0/4] Convert remaining buses to generic driver_override handling

[Danilo Krummrich]

On Thu Jun 4, 2026 at 5:52 AM CEST, Runyu Xiao wrote:
> Runyu Xiao (4):
>   amba: use generic driver_override infrastructure
>   rpmsg: core: use generic driver_override infrastructure
>   vmbus: use generic driver_override infrastructure
>   cdx: use generic driver_override infrastructure

Given that you changed the approach to use the new driver_override
infrastructure, I assume you read the message in [1]?

In this message I also explained that this all has been addressed and was merged
into driver-core-next already.

[1] https://lore.kernel.org/all/DIYPR0K2CZW7.254R8K7ONBX5D@kernel.org/