Re: [PATCH] block: improve ioprio value validity checks

[Niklas Cassel <Niklas.Cassel@wdc.com>]

On Tue, May 30, 2023 at 03:13:07PM +0900, Damien Le Moal wrote:
> The introduction of the macro IOPRIO_PRIO_LEVEL() in commit
> eca2040972b4 ("scsi: block: ioprio: Clean up interface definition")
> results in an iopriority level to always be masked using the macro
> IOPRIO_LEVEL_MASK, and thus to the kernel always seeing an acceptable
> value for an I/O priority level when checked in ioprio_check_cap().
> Before this patch, this function would return an error for some (but not
> all) invalid values for a level valid range of [0..7].
> 
> Restore and improve the detection of invalid priority levels by
> introducing the inline function ioprio_value() to check an ioprio class,
> level and hint value before combining these fields into a single value
> to be used with ioprio_set() or AIOs. If an invalid value for the class,
> level or hint of an ioprio is detected, ioprio_value() returns an ioprio
> using the class IOPRIO_CLASS_INVALID, indicating an invalid value and
> causing ioprio_check_cap() to return -EINVAL.
> 
> Fixes: 6c913257226a ("scsi: block: Introduce ioprio hints")
> Fixes: eca2040972b4 ("scsi: block: ioprio: Clean up interface definition")
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>  block/ioprio.c              |  1 +
>  include/uapi/linux/ioprio.h | 47 +++++++++++++++++++++++--------------
>  2 files changed, 31 insertions(+), 17 deletions(-)
> 
> diff --git a/block/ioprio.c b/block/ioprio.c
> index f0d9e818abc5..b5a942519a79 100644
> --- a/block/ioprio.c
> +++ b/block/ioprio.c
> @@ -58,6 +58,7 @@ int ioprio_check_cap(int ioprio)
>  			if (level)
>  				return -EINVAL;
>  			break;
> +		case IOPRIO_CLASS_INVALID:
>  		default:
>  			return -EINVAL;
>  	}
> diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h
> index 607c7617b9d2..7310449c0178 100644
> --- a/include/uapi/linux/ioprio.h
> +++ b/include/uapi/linux/ioprio.h
> @@ -6,15 +6,13 @@
>   * Gives us 8 prio classes with 13-bits of data for each class
>   */
>  #define IOPRIO_CLASS_SHIFT	13
> -#define IOPRIO_CLASS_MASK	0x07
> +#define IOPRIO_NR_CLASSES	8
> +#define IOPRIO_CLASS_MASK	(IOPRIO_NR_CLASSES - 1)
>  #define IOPRIO_PRIO_MASK	((1UL << IOPRIO_CLASS_SHIFT) - 1)
>  
>  #define IOPRIO_PRIO_CLASS(ioprio)	\
>  	(((ioprio) >> IOPRIO_CLASS_SHIFT) & IOPRIO_CLASS_MASK)
>  #define IOPRIO_PRIO_DATA(ioprio)	((ioprio) & IOPRIO_PRIO_MASK)
> -#define IOPRIO_PRIO_VALUE(class, data)	\
> -	((((class) & IOPRIO_CLASS_MASK) << IOPRIO_CLASS_SHIFT) | \
> -	 ((data) & IOPRIO_PRIO_MASK))
>  
>  /*
>   * These are the io priority classes as implemented by the BFQ and mq-deadline
> @@ -25,10 +23,13 @@
>   * served when no one else is using the disk.
>   */
>  enum {
> -	IOPRIO_CLASS_NONE,
> -	IOPRIO_CLASS_RT,
> -	IOPRIO_CLASS_BE,
> -	IOPRIO_CLASS_IDLE,
> +	IOPRIO_CLASS_NONE	= 0,
> +	IOPRIO_CLASS_RT		= 1,
> +	IOPRIO_CLASS_BE		= 2,
> +	IOPRIO_CLASS_IDLE	= 3,
> +
> +	/* Special class to indicate an invalid ioprio value */
> +	IOPRIO_CLASS_INVALID	= 7,
>  };
>  
>  /*
> @@ -73,15 +74,6 @@ enum {
>  #define IOPRIO_PRIO_HINT(ioprio)	\
>  	(((ioprio) >> IOPRIO_HINT_SHIFT) & IOPRIO_HINT_MASK)
>  
> -/*
> - * Alternate macro for IOPRIO_PRIO_VALUE() to define an IO priority with
> - * a class, level and hint.
> - */
> -#define IOPRIO_PRIO_VALUE_HINT(class, level, hint)		 \
> -	((((class) & IOPRIO_CLASS_MASK) << IOPRIO_CLASS_SHIFT) | \
> -	 (((hint) & IOPRIO_HINT_MASK) << IOPRIO_HINT_SHIFT) |	 \
> -	 ((level) & IOPRIO_LEVEL_MASK))
> -
>  /*
>   * IO hints.
>   */
> @@ -107,4 +99,25 @@ enum {
>  	IOPRIO_HINT_DEV_DURATION_LIMIT_7 = 7,
>  };
>  
> +#define IOPRIO_BAD_VALUE(val, max) ((val) < 0 || (val) >= (max))
> +
> +/*
> + * Return an I/O priority value based on a class, a level and a hint.
> + */
> +static __always_inline __u16 ioprio_value(int class, int level, int hint)
> +{
> +	if (IOPRIO_BAD_VALUE(class, IOPRIO_NR_CLASSES) ||
> +	    IOPRIO_BAD_VALUE(level, IOPRIO_NR_LEVELS) ||
> +	    IOPRIO_BAD_VALUE(hint, IOPRIO_NR_HINTS))
> +		return IOPRIO_CLASS_INVALID << IOPRIO_CLASS_SHIFT;
> +
> +	return (class << IOPRIO_CLASS_SHIFT) |
> +		(hint << IOPRIO_HINT_SHIFT) | level;
> +}
> +
> +#define IOPRIO_PRIO_VALUE(class, level)			\
> +	ioprio_value(class, level, IOPRIO_HINT_NONE)
> +#define IOPRIO_PRIO_VALUE_HINT(class, level, hint)	\
> +	ioprio_value(class, level, hint)
> +
>  #endif /* _UAPI_LINUX_IOPRIO_H */
> -- 
> 2.40.1
> 

It seems a bit unfortunate that we need to "allocate" a priority class
just in order to detect values out of range, but considering that this
enables out of range checking for class, level, and hint, I think that
this it is worth it. (Especially since there wasn't any _reliable_ out
of range checking done before.)

Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>