From: Kees Cook <keescook@chromium.org>
To: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Feng Tang <feng.tang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
Hyeonggon Yoo <42.hyeyoo@gmail.com>,
Dmitry Vyukov <dvyukov@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Dave Hansen <dave.hansen@intel.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH v6 2/4] mm/slub: only zero the requested size of buffer for kzalloc
Date: Mon, 26 Sep 2022 13:15:02 -0700 [thread overview]
Message-ID: <202209261305.CF6ED6EEC@keescook> (raw)
In-Reply-To: <CA+fCnZfSv98uvxop7YN_L-F=WNVkb5rcwa6Nmf5yN-59p8Sr4Q@mail.gmail.com>
On Mon, Sep 26, 2022 at 09:11:24PM +0200, Andrey Konovalov wrote:
> On Tue, Sep 13, 2022 at 8:54 AM Feng Tang <feng.tang@intel.com> wrote:
> >
>
> Hi Feng,
>
> > kzalloc/kmalloc will round up the request size to a fixed size
> > (mostly power of 2), so the allocated memory could be more than
> > requested. Currently kzalloc family APIs will zero all the
> > allocated memory.
> >
> > To detect out-of-bound usage of the extra allocated memory, only
> > zero the requested part, so that sanity check could be added to
> > the extra space later.
>
> I still don't like the idea of only zeroing the requested memory and
> not the whole object. Considering potential info-leak vulnerabilities.
I really really do not like reducing the zeroing size. We're trying to
be proactive against _flaws_, which means that when there's a memory
over-read (or uninitialized use), suddenly the scope of the exposure (or
control) is wider/looser.
Imagine the (unfortunately very common) case of use-after-free attacks,
which leverage type confusion: some object is located in kmalloc-128
because it's 126 bytes. That slot gets freed and reallocated to, say, a
97 byte object going through kzalloc() or zero-on-init. With this patch
the bytes above the 97 don't get zeroed, and the stale data from the
prior 126 byte object say there happily to be used again later through
a dangling pointer, or whatever. Without the proposed patch, the entire
128 bytes is wiped, which makes stale data re-use more difficult.
> > Performance wise, smaller zeroing length also brings shorter
> > execution time, as shown from test data on various server/desktop
> > platforms.
For these cases, I think a much better solution is to provide those
sensitive allocations their own dedicated kmem_cache.
> >
> > For kzalloc users who will call ksize() later and utilize this
> > extra space, please be aware that the space is not zeroed any
> > more.
>
> CC Kees
Thanks! Well, the good news is that ksize() side-effects is hopefully
going to vanish soon, but my objections about stale memory remain.
-Kees
--
Kees Cook
next prev parent reply other threads:[~2022-09-26 20:15 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 6:54 [PATCH v6 0/4] mm/slub: some debug enhancements for kmalloc Feng Tang
2022-09-13 6:54 ` [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc Feng Tang
2022-09-23 11:43 ` Vlastimil Babka
2022-09-24 7:08 ` Feng Tang
2022-10-30 19:23 ` John Thomson
2022-10-30 21:30 ` Vlastimil Babka
2022-10-31 2:36 ` Feng Tang
2022-10-31 10:05 ` John Thomson
2022-10-31 11:36 ` Hyeonggon Yoo
2022-10-31 11:42 ` Feng Tang
2022-11-01 0:18 ` John Thomson
2022-11-01 2:41 ` John Thomson
2022-11-01 7:57 ` Feng Tang
2022-11-01 9:20 ` John Thomson
2022-11-01 9:31 ` Hyeonggon Yoo
2022-11-01 10:33 ` John Thomson
2022-11-01 10:42 ` Hyeonggon Yoo
2022-11-01 13:55 ` Feng Tang
2022-11-01 19:39 ` John Thomson
2022-11-02 6:08 ` Feng Tang
2022-11-02 7:16 ` Hyeonggon Yoo
2022-11-03 7:18 ` Feng Tang
2022-11-03 7:45 ` John Thomson
2022-11-03 8:16 ` Feng Tang
2022-11-02 8:22 ` Vlastimil Babka
2022-11-03 5:54 ` Feng Tang
2022-11-03 8:33 ` Vlastimil Babka
2022-11-03 14:16 ` Feng Tang
2022-11-03 14:36 ` Hyeonggon Yoo
2022-11-03 16:57 ` Vlastimil Babka
2022-11-03 17:35 ` Vlastimil Babka
2022-11-04 3:52 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 2/4] mm/slub: only zero the requested size of buffer for kzalloc Feng Tang
2022-09-26 19:11 ` Andrey Konovalov
2022-09-26 20:15 ` Kees Cook [this message]
2022-09-27 1:22 ` Feng Tang
2022-09-27 2:42 ` Feng Tang
2022-10-13 14:00 ` Andrey Konovalov
2022-10-14 5:59 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct kasan_cache Feng Tang
2022-09-20 19:20 ` Andrey Konovalov
2022-09-21 12:02 ` Feng Tang
2022-09-24 18:05 ` Andrey Konovalov
2022-09-25 11:26 ` Feng Tang
2022-09-25 16:31 ` Andrey Konovalov
2022-09-27 3:03 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 4/4] mm/slub: extend redzone check to extra allocated kmalloc space than requested Feng Tang
2022-09-13 8:53 ` Hyeonggon Yoo
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