Re: [PATCH] leds: leds-mt6323: Adjust return/parameter types in wled get/set callbacks

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 22/06/23 18:12, Nathan Chancellor ha scritto:
> Clang's kernel Control Flow Integrity (kCFI) is a compiler-based
> security mitigation that ensures the target of an indirect function call
> matches the expected type of the call and trapping if they do not match
> exactly. The warning -Wincompatible-function-pointer-types-strict aims
> to catch these issues at compile time, which reveals:
> 
>   drivers/leds/leds-mt6323.c:598:49: error: incompatible function pointer types assigning to 'int (*)(struct led_classdev *, enum led_brightness)' from 'int (struct led_classdev *, unsigned int)' [-Werror,-Wincompatible-function-pointer-types-strict]
>     598 |                         leds->led[reg]->cdev.brightness_set_blocking =
>         |                                                                      ^
>     599 |                                                 mt6323_wled_set_brightness;
>         |                                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~
>   drivers/leds/leds-mt6323.c:600:40: error: incompatible function pointer types assigning to 'enum led_brightness (*)(struct led_classdev *)' from 'unsigned int (struct led_classdev *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>     600 |                         leds->led[reg]->cdev.brightness_get =
>         |                                                             ^
>     601 |                                                 mt6323_get_wled_brightness;
>         |                                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~
>   2 errors generated.
> 
> While 'unsigned int' is ABI compatible with 'enum led_brightness' (hence
> no warning from -Wincompatible-function-pointer-types) and the callers
> of these callbacks use/pass the values as 'unsigned int', the mismatch
> between the prototype and the called function will trip kCFI at runtime.
> 
> Change the types in the implementations to match the prototypes, clearing
> up the warning and avoiding kCFI failures.
> 
> Fixes: 9bb0a9e0626c ("leds: leds-mt6323: Add support for WLEDs and MT6332")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

leds need to deprecate said enumeration for real, since it's marked for
deprecation but, in the meanwhile, we can't have kCFI failures on this driver.

For this reason,

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

Cheers,
Angelo

> ---
>   drivers/leds/leds-mt6323.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/leds/leds-mt6323.c b/drivers/leds/leds-mt6323.c
> index e8fecfc2e90a..24f35bdb55fb 100644
> --- a/drivers/leds/leds-mt6323.c
> +++ b/drivers/leds/leds-mt6323.c
> @@ -76,7 +76,7 @@ struct mt6323_led {
>   	int			id;
>   	struct mt6323_leds	*parent;
>   	struct led_classdev	cdev;
> -	unsigned int		current_brightness;
> +	enum led_brightness	current_brightness;
>   };
>   
>   /**
> @@ -451,7 +451,7 @@ static int mtk_wled_hw_off(struct led_classdev *cdev)
>   	return 0;
>   }
>   
> -static unsigned int mt6323_get_wled_brightness(struct led_classdev *cdev)
> +static enum led_brightness mt6323_get_wled_brightness(struct led_classdev *cdev)
>   {
>   	struct mt6323_led *led = container_of(cdev, struct mt6323_led, cdev);
>   	struct mt6323_leds *leds = led->parent;
> @@ -471,7 +471,7 @@ static unsigned int mt6323_get_wled_brightness(struct led_classdev *cdev)
>   }
>   
>   static int mt6323_wled_set_brightness(struct led_classdev *cdev,
> -				      unsigned int brightness)
> +				      enum led_brightness brightness)
>   {
>   	struct mt6323_led *led = container_of(cdev, struct mt6323_led, cdev);
>   	struct mt6323_leds *leds = led->parent;
> 
> ---
> base-commit: 7bd932d9adbcc5c5370d968bdb0b00385606bf3a
> change-id: 20230621-mt6323-wled-wincompatible-function-pointer-types-strict-334f06d92ffb
> 
> Best regards,