Re: [PATCH] kasan, slub: fix HW_TAGS zeroing with slub_debug

[Will Deacon]

On Wed, Jul 05, 2023 at 03:19:06PM +0200, Andrey Konovalov wrote:
> On Wed, Jul 5, 2023 at 2:51 PM Marco Elver <elver@xxxxxxxxxx> wrote:
> >
> > On Wed, 5 Jul 2023 at 14:44, <andrey.konovalov@xxxxxxxxx> wrote:
> > >
> > > From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > >
> > > Commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated
> > > kmalloc space than requested") added precise kmalloc redzone poisoning
> > > to the slub_debug functionality.
> > >
> > > However, this commit didn't account for HW_TAGS KASAN fully initializing
> > > the object via its built-in memory initialization feature. Even though
> > > HW_TAGS KASAN memory initialization contains special memory initialization
> > > handling for when slub_debug is enabled, it does not account for in-object
> > > slub_debug redzones. As a result, HW_TAGS KASAN can overwrite these
> > > redzones and cause false-positive slub_debug reports.
> > >
> > > To fix the issue, avoid HW_TAGS KASAN memory initialization when slub_debug
> > > is enabled altogether. Implement this by moving the __slub_debug_enabled
> > > check to slab_post_alloc_hook. Common slab code seems like a more
> > > appropriate place for a slub_debug check anyway.
> > >
> > > Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested")
> > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
> >
> > Is it fixing this issue:
> >
> >   https://lore.kernel.org/all/20230628154714.GB22090@willie-the-truck/
> 
> Yes, my bad, messed up the Reported-by tag. The correct one should be:
> 
> Reported-by: Will Deacon <will@xxxxxxxxxx>
> 
> > Other than the question above, it looks sane:
> >
> > Acked-by: Marco Elver <elver@xxxxxxxxxx>
> 
> Thank you, Marco!

Cheers, this seems to fix the splats for me:

Tested-by: Will Deacon <will@xxxxxxxxxx>

Will