[PATCH] iosys-map: Fix undefined behavior in iosys_map_clear()

[Gote, Nitin R]

Hi Thomas,

> 
> Hi
> 
> Am 18.07.25 um 16:47 schrieb Andi Shyti:
> > Hi Nitin,
> >
> > On Fri, Jul 18, 2025 at 04:20:51PM +0530, Nitin Gote wrote:
> >> The current iosys_map_clear() implementation reads the potentially
> >> uninitialized 'is_iomem' boolean field to decide which union member
> >> to clear. This causes undefined behavior when called on uninitialized
> >> structures, as 'is_iomem' may contain garbage values like 0xFF.
> >>
> >> UBSAN detects this as:
> >>      UBSAN: invalid-load in include/linux/iosys-map.h:267
> >>      load of value 255 is not a valid value for type '_Bool'
> >>
> >> Fix by unconditionally clearing the entire structure with memset(),
> >> eliminating the need to read uninitialized data and ensuring all
> >> fields are set to known good values.
> >>
> >> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14639
> >> Fixes: 01fd30da0474 ("dma-buf: Add struct dma-buf-map for storing
> >> struct dma_buf.vaddr_ptr")
> >> Signed-off-by: Nitin Gote <nitin.r.gote at intel.com>
> > +Thomas and the dri-devel mailing list.
> >
> > In any case, your patch makes sense to me:
> 
> The call to iosys_map_clear() is at
> 
> https://elixir.bootlin.com/linux/v6.15.6/source/drivers/dma-buf/dma-
> buf.c#L1571
> 
> It's a defensive measure for cases where the caller reads the returned map
> address when it was never initialized by the vmap implementation.
> I'm not a big fan of memset(), but OK. Preferably, iosys_map_clear() would simply
> set vaddr = NULL and is_iomem = false. Anyway,
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
> 
> Best regards
> Thomas
> 

Thank you for the review.
Could you please help to merge this patch? 

- Nitin

> >
> > Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>
> >
> > Andi
> >
> >> ---
> >>   include/linux/iosys-map.h | 7 +------
> >>   1 file changed, 1 insertion(+), 6 deletions(-)
> >>
> >> diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h
> >> index 4696abfd311c..3e85afe794c0 100644
> >> --- a/include/linux/iosys-map.h
> >> +++ b/include/linux/iosys-map.h
> >> @@ -264,12 +264,7 @@ static inline bool iosys_map_is_set(const struct
> iosys_map *map)
> >>    */
> >>   static inline void iosys_map_clear(struct iosys_map *map)
> >>   {
> >> -	if (map->is_iomem) {
> >> -		map->vaddr_iomem = NULL;
> >> -		map->is_iomem = false;
> >> -	} else {
> >> -		map->vaddr = NULL;
> >> -	}
> >> +	memset(map, 0, sizeof(*map));
> >>   }
> >>
> >>   /**
> >> --
> >> 2.25.1
> 
> --
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809
> (AG Nuernberg)