Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags

[Arnd Bergmann]

On Fri, Jul 21, 2023, at 12:22, Peter Zijlstra wrote:
>   * futex_parse_waitv - Parse a waitv array from userspace
> @@ -207,7 +207,12 @@ static int futex_parse_waitv(struct fute
>  		if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
>  			return -EINVAL;
> 
> -		if (!(aux.flags & FUTEX2_32))
> +		if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> +			if ((aux.flags & FUTEX2_64) == FUTEX2_64)
> +				return -EINVAL;
> +		}
> +
> +		if ((aux.flags & FUTEX2_64) != FUTEX2_32)
>  			return -EINVAL;

This looks slightly confusing, how about defining another
FUTEX2_SIZEMASK (or similar) macro to clarify that
"aux.flags & FUTEX2_64" is a mask operation that can
match the FUTEX2_{8,16,32,64} values?

       Arnd