linux-kernel - Re: [PATCH 1/2] kasan, mm: fix conflicts with init_on

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Message-ID: <CAAeHK+xgdS+vSTN81uLzahB9BYf=+iJdckwS=v7AwRACAf0wfw@mail.gmail.com>
Date:   Thu, 14 Jan 2021 16:31:52 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kasan, mm: fix conflicts with init_on_alloc/free

On Wed, Jan 13, 2021 at 6:25 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 1/13/21 5:03 PM, Andrey Konovalov wrote:
> > A few places where SLUB accesses object's data or metadata were missed in
> > a previous patch. This leads to false positives with hardware tag-based
> > KASAN when bulk allocations are used with init_on_alloc/free.
> >
> > Fix the false-positives by resetting pointer tags during these accesses.
> >
> > Link: https://linux-review.googlesource.com/id/I50dd32838a666e173fe06c3c5c766f2c36aae901
> > Fixes: aa1ef4d7b3f67 ("kasan, mm: reset tags when accessing metadata")
> > Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>
> > ---
> >  mm/slub.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index dc5b42e700b8..75fb097d990d 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2791,7 +2791,8 @@ static __always_inline void maybe_wipe_obj_freeptr(struct kmem_cache *s,
> >                                                  void *obj)
> >  {
> >       if (unlikely(slab_want_init_on_free(s)) && obj)
> > -             memset((void *)((char *)obj + s->offset), 0, sizeof(void *));
> > +             memset((void *)((char *)kasan_reset_tag(obj) + s->offset),
> > +                     0, sizeof(void *));
> >  }
> >
> >  /*
> > @@ -2883,7 +2884,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
> >               stat(s, ALLOC_FASTPATH);
> >       }
> >
> > -     maybe_wipe_obj_freeptr(s, kasan_reset_tag(object));
> > +     maybe_wipe_obj_freeptr(s, object);
>
> And in that case the reset was unnecessary, right. (commit log only mentions
> adding missing resets).

The reset has been moved into maybe_wipe_obj_freeptr(). I'll mention
it in the changelog in v2.

Thanks!