From: Feng Tang <feng.tang@intel.com>
To: Kees Cook <keescook@chromium.org>,
Andrey Konovalov <andreyknvl@gmail.com>
Cc: 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>,
"Hansen, Dave" <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: Tue, 27 Sep 2022 09:22:55 +0800 [thread overview]
Message-ID: <YzJQb2znPB1fDjVE@feng-clx> (raw)
In-Reply-To: <202209261305.CF6ED6EEC@keescook>
On Tue, Sep 27, 2022 at 04:15:02AM +0800, Kees Cook wrote:
> 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.
Thanks for the details explaination, which is a valid concern.
And Andrey's suggestion is a good solution: only reduce the zeroing
size for kmalloc-redzone enabled objects, as the extra space will be
redzoned, and no info will be leaked.
Thanks,
Feng
next prev parent reply other threads:[~2022-09-27 1:23 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
2022-09-27 1:22 ` Feng Tang [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YzJQb2znPB1fDjVE@feng-clx \
--to=feng.tang@intel.com \
--cc=42.hyeyoo@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=andreyknvl@gmail.com \
--cc=cl@linux.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@intel.com \
--cc=dvyukov@google.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=kasan-dev@googlegroups.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=roman.gushchin@linux.dev \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).