linux-kernel - Re: [PATCH v5 3/4] mm: kasan: Add free_meta size info in struct kasan

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Date:   Sun, 11 Sep 2022 13:51:54 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "Sang, Oliver" <oliver.sang@...el.com>
Subject: Re: [PATCH v5 3/4] mm: kasan: Add free_meta size info in struct kasan_cache

On Sun, Sep 11, 2022 at 5:57 AM Feng Tang <feng.tang@...el.com> wrote:
>
> Hi Andrey,
>
> Thanks for reviewing this series!
>
> On Sun, Sep 11, 2022 at 07:14:55AM +0800, Andrey Konovalov wrote:
> > On Wed, Sep 7, 2022 at 9:11 AM Feng Tang <feng.tang@...el.com> wrote:
> > >
> > > When kasan is enabled for slab/slub, it may save kasan' free_meta
> > > data in the former part of slab object data area in slab object
> > > free path, which works fine.
> > >
> > > There is ongoing effort to extend slub's debug function which will
> > > redzone the latter part of kmalloc object area, and when both of
> > > the debug are enabled, there is possible conflict, especially when
> > > the kmalloc object has small size, as caught by 0Day bot [1]
> > >
> > > For better information for slab/slub, add free_meta's data size
> > > into 'struct kasan_cache', so that its users can take right action
> > > to avoid data conflict.
> > >
> > > [1]. https://lore.kernel.org/lkml/YuYm3dWwpZwH58Hu@xsang-OptiPlex-9020/
> > > Reported-by: kernel test robot <oliver.sang@...el.com>
> > > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > > Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
> > > ---
> > >  include/linux/kasan.h | 2 ++
> > >  mm/kasan/common.c     | 2 ++
> > >  2 files changed, 4 insertions(+)
> > >
> > > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > > index b092277bf48d..293bdaa0ba09 100644
> > > --- a/include/linux/kasan.h
> > > +++ b/include/linux/kasan.h
> > > @@ -100,6 +100,8 @@ static inline bool kasan_has_integrated_init(void)
> > >  struct kasan_cache {
> > >         int alloc_meta_offset;
> > >         int free_meta_offset;
> > > +       /* size of free_meta data saved in object's data area */
> > > +       int free_meta_size_in_object;
> >
> > I thinks calling this field free_meta_size is clear enough. Thanks!
>
> Yes, the name does look long. The "in_object" was added to make it
> also a flag for whether the free meta is saved inside object's data
> area.
>
> For 'free_meta_size', the code logic in slub should be:
>
>   if (info->free_meta_offset == 0 &&
>         info->free_meta_size >= ...)

I'd say you can keep the current logic and just rename the field to
make it shorter. But up to you, I'm fine with either approach. Thanks!