linux-kernel - Re: [PATCH RFC v2 2/6] mm/slab: Perform init_on

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Date:   Wed, 30 Sep 2020 14:50:59 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>,
        Will Deacon <will@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        David Howells <dhowells@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Laura Abbott <labbott@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Micay <danielmicay@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Machek <pavel@...x.de>,
        Valentin Schneider <valentin.schneider@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>, notify@...nel.org
Subject: Re: [PATCH RFC v2 2/6] mm/slab: Perform init_on_free earlier

On Tue, Sep 29, 2020 at 8:35 PM Alexander Popov <alex.popov@...ux.com> wrote:
>
> Currently in CONFIG_SLAB init_on_free happens too late, and heap
> objects go to the heap quarantine being dirty. Lets move memory
> clearing before calling kasan_slab_free() to fix that.
>
> Signed-off-by: Alexander Popov <alex.popov@...ux.com>
Reviewed-by: Alexander Potapenko <glider@...gle.com>

> ---
>  mm/slab.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 3160dff6fd76..5140203c5b76 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3414,6 +3414,9 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
>  static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
>                                          unsigned long caller)
>  {
> +       if (unlikely(slab_want_init_on_free(cachep)))
> +               memset(objp, 0, cachep->object_size);
> +
>         /* Put the object into the quarantine, don't touch it for now. */
>         if (kasan_slab_free(cachep, objp, _RET_IP_))
>                 return;
> @@ -3432,8 +3435,6 @@ void ___cache_free(struct kmem_cache *cachep, void *objp,
>         struct array_cache *ac = cpu_cache_get(cachep);
>
>         check_irq_off();
> -       if (unlikely(slab_want_init_on_free(cachep)))
> -               memset(objp, 0, cachep->object_size);
>         kmemleak_free_recursive(objp, cachep->flags);
>         objp = cache_free_debugcheck(cachep, objp, caller);
>         memcg_slab_free_hook(cachep, virt_to_head_page(objp), objp);
> --
> 2.26.2
>


-- 
Alexander Potapenko
Software Engineer

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