From: Marco Elver <elver@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] slub: Avoid redzone when choosing freepointer location
Date: Wed, 15 Apr 2020 20:07:57 +0200 [thread overview]
Message-ID: <CANpmjNPORrwPkqByhtKgVoh5=KHkpYHM0zRv6O1RgONmx3ZqOg@mail.gmail.com> (raw)
In-Reply-To: <202004151054.BD695840@keescook>
On Wed, 15 Apr 2020 at 19:55, Kees Cook <keescook@chromium.org> wrote:
>
> Marco Elver reported system crashes when booting with "slub_debug=Z".
> The freepointer location (s->offset) was not taking into account that
> the "inuse" size that includes the redzone area should not be used by
> the freelist pointer. Change the calculation to save the area of the
> object that an inline freepointer may be written into.
>
> Reported-by: Marco Elver <elver@google.com>
> Link: https://lore.kernel.org/linux-mm/20200415164726.GA234932@google.com
> Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
> Signed-off-by: Kees Cook <keescook@chromium.org>
Works for me, thank you!
Tested-by: Marco Elver <elver@google.com>
> ---
> mm/slub.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 332d4b459a90..9bf44955c4f1 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3533,6 +3533,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> {
> slab_flags_t flags = s->flags;
> unsigned int size = s->object_size;
> + unsigned int freepointer_area;
> unsigned int order;
>
> /*
> @@ -3541,6 +3542,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> * the possible location of the free pointer.
> */
> size = ALIGN(size, sizeof(void *));
> + /*
> + * This is the area of the object where a freepointer can be
> + * safely written. If redzoning adds more to the inuse size, we
> + * can't use that portion for writing the freepointer, so
> + * s->offset must be limited within this for the general case.
> + */
> + freepointer_area = size;
>
> #ifdef CONFIG_SLUB_DEBUG
> /*
> @@ -3582,13 +3590,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> */
> s->offset = size;
> size += sizeof(void *);
> - } else if (size > sizeof(void *)) {
> + } else if (freepointer_area > sizeof(void *)) {
> /*
> * Store freelist pointer near middle of object to keep
> * it away from the edges of the object to avoid small
> * sized over/underflows from neighboring allocations.
> */
> - s->offset = ALIGN(size / 2, sizeof(void *));
> + s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
> }
>
> #ifdef CONFIG_SLUB_DEBUG
> --
> 2.20.1
>
>
> --
> Kees Cook
prev parent reply other threads:[~2020-04-15 18:08 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 17:55 [PATCH] slub: Avoid redzone when choosing freepointer location Kees Cook
2020-04-15 18:07 ` Marco Elver [this message]
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