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Date: Tue, 18 Aug 2020 12:08:47 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Kees Cook <keescook@...omium.org>
Cc: Jann Horn <jannh@...gle.com>, Will Deacon <will@...nel.org>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.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>, kasan-dev@...glegroups.com,
linux-mm@...ck.org, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, notify@...nel.org,
Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH RFC 0/2] Break heap spraying needed for exploiting
use-after-free
On 15.08.2020 19:39, Kees Cook wrote:
> On Thu, Aug 13, 2020 at 06:19:20PM +0300, Alexander Popov wrote:
>> I've found an easy way to break heap spraying for use-after-free
>> exploitation. I simply extracted slab freelist quarantine from KASAN
>> functionality and called it CONFIG_SLAB_QUARANTINE. Please see patch 1.
>
> Ah yeah, good idea. :)
>
>> [...]
>> I did a brief performance evaluation of this feature.
>>
>> 1. Memory consumption. KASAN quarantine uses 1/32 of the memory.
>> CONFIG_SLAB_QUARANTINE disabled:
>> # free -m
>> total used free shared buff/cache available
>> Mem: 1987 39 1862 10 86 1907
>> Swap: 0 0 0
>> CONFIG_SLAB_QUARANTINE enabled:
>> # free -m
>> total used free shared buff/cache available
>> Mem: 1987 140 1760 10 87 1805
>> Swap: 0 0 0
>
> 1/32 of memory doesn't seem too bad for someone interested in this defense.
This can be configured. Quote from linux/mm/kasan/quarantine.c:
/*
* The fraction of physical memory the quarantine is allowed to occupy.
* Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
* the ratio low to avoid OOM.
*/
#define QUARANTINE_FRACTION 32
>> 2. Performance penalty. I used `hackbench -s 256 -l 200 -g 15 -f 25 -P`.
>> CONFIG_SLAB_QUARANTINE disabled (x86_64, CONFIG_SLUB):
>> Times: 3.088, 3.103, 3.068, 3.103, 3.107
>> Mean: 3.0938
>> Standard deviation: 0.0144
>> CONFIG_SLAB_QUARANTINE enabled (x86_64, CONFIG_SLUB):
>> Times: 3.303, 3.329, 3.356, 3.314, 3.292
>> Mean: 3.3188 (+7.3%)
>> Standard deviation: 0.0223
>
> That's rather painful, but hackbench can produce some big deltas given
> it can be an unrealistic workload for most systems. I'd be curious to
> see the "building a kernel" timings, which tends to be much more
> realistic for "busy system" without hammering one particular subsystem
> (though it's a bit VFS heavy, obviously).
I have new results.
CPU: Intel Core i7-6500U CPU @ 2.50GHz
Test: time make O=../build_out/defconfig/ -j2
CONFIG_SLAB_QUARANTINE disabled:
Times: 10m52.978s 10m50.161s 10m45.601s
Mean: 649.58s
Standard deviation: 3.04
CONFIG_SLAB_QUARANTINE enabled:
Times: 10m56.256s 10m51.919s 10m47.903s
Mean: 652.026s (+0,38%)
Standard deviation: 3.41
This test shows much lower performance penalty.
More ideas of tests?
Best regards,
Alexander
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