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

[Peter Zijlstra]

On Fri, Jul 21, 2023 at 05:47:31PM +0200, Arnd Bergmann wrote:
> 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?

Yeah, I had that in an earlier version, but then reconsidered as I
didn't want to clutter the uabi with that. But perhaps I over-throught
this.