Re: [PATCH v2 2/2] Add TAINT_DRIVER_OVERRIDE for usage of driver_override

["Danilo Krummrich" <dakr@kernel.org>]

On Sun Sep 27, 2026 at 11:55 AM CEST, Danilo Krummrich wrote:
> On Sun Sep 27, 2026 at 10:03 AM CEST, Uwe Kleine-König wrote:
>> Commit fcbfaffee51a ("driver core: add TAINT_FORCED_BIND for when
>> userspace manually messes with devices and drivers") introduced a taint
>> for usage of bind/unbind sysfs files that manually trigger driver probe
>> and remove respectively.
>>
>> For drivers that do their resource management correctly (which is also
>> needed for module unloading) bind and unbind for matching devices are
>> not critical operations. The thing that makes bind and unbind unsafe is
>> that drivers can be forced on devices that originally don't match using
>> driver_override. The result is that e.g. of_device_get_match_data()
>> returns NULL despite all .of_match_table entries having a non-NULL
>> .driver_data member which yields a NULL pointer exception for several
>> drivers. And given that after setting a driver_override a manual bind is
>> only one way a driver can be bound to an unexpected device, a separate
>> taint for such an override is justified.
>>
>> Reviewed-by: Bradley Morgan <brads@mainlining.org>
>> Reviewed-by: Armin Wolf <W_Armin@gmx.de>
>> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
>
> Suggested-by: Danilo Krummrich <dakr@kernel.org>
> Link: https://lore.kernel.org/driver-core/DLIL9H50MALI.3JROXYEEUM3KU@kernel.org/
>
>> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
>> index c51ad96d4de4..7d5dc016a457 100644
>> --- a/drivers/base/bus.c
>> +++ b/drivers/base/bus.c
>> @@ -513,6 +513,7 @@ static ssize_t driver_override_store(struct device *dev,
>>  {
>>  	int ret;
>>  
>> +	add_taint_module(NULL, TAINT_DRIVER_OVERRIDE, LOCKDEP_STILL_OK);
>>  	ret = __device_set_driver_override(dev, buf, count);
>
> There are buses (such as SPI) which unfortunately have to call
> __device_set_driver_override() directly.
>
> I think it would be better to move the taint into __device_set_driver_override()
> and properly document the purpose of __device_set_driver_override().

Of course I meant to say to create a new forwarding function for this purpose,
such that we do not taint for device_set_driver_override().

Maybe device_store_driver_override() or device_set_driver_override_store()?

> It only exists as SPI and AP are a bit special; both print "\n" when
> driver_override is not set, whereas all other buses (and thus the driver-core)
> produce "(null)\n" in this case. I.e. it should never get any new users.
>
> Thanks,
> Danilo