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Message-ID: <c6d3b4ce-cdb1-4bc9-d899-89228b4219cd@linux.com>
Date: Tue, 18 Aug 2020 00:03:57 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Pavel Machek <pavel@...x.de>, Matthew Wilcox <willy@...radead.org>
Cc: Kees Cook <keescook@...omium.org>, 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 1/2] mm: Extract SLAB_QUARANTINE from KASAN
On 16.08.2020 22:59, Pavel Machek wrote:
> On Sat 2020-08-15 19:54:55, Matthew Wilcox wrote:
>> On Thu, Aug 13, 2020 at 06:19:21PM +0300, Alexander Popov wrote:
>>> +config SLAB_QUARANTINE
>>> + bool "Enable slab freelist quarantine"
>>> + depends on !KASAN && (SLAB || SLUB)
>>> + help
>>> + Enable slab freelist quarantine to break heap spraying technique
>>> + used for exploiting use-after-free vulnerabilities in the kernel
>>> + code. If this feature is enabled, freed allocations are stored
>>> + in the quarantine and can't be instantly reallocated and
>>> + overwritten by the exploit performing heap spraying.
>>> + This feature is a part of KASAN functionality.
>>
>> After this patch, it isn't part of KASAN any more ;-)
>>
>> The way this is written is a bit too low level. Let's write it in terms
>> that people who don't know the guts of the slab allocator or security
>> terminology can understand:
>>
>> Delay reuse of freed slab objects. This makes some security
>> exploits harder to execute. It reduces performance slightly
>> as objects will be cache cold by the time they are reallocated,
>> and it costs a small amount of memory.
>
> Written this way, it invites questions:
>
> Does it introduce any new deadlocks in near out-of-memory situations?
Linux kernel with enabled KASAN is heavily tested by syzbot.
I think Dmitry and Andrey can give good answers to your question.
Some time ago I was doing Linux kernel fuzzing with syzkaller on low memory
virtual machines (with KASAN and LOCKUP_DETECTOR enabled). I gave less than 1G
to each debian stretch VM. I didn't get any special deadlock caused by OOM.
Best regards,
Alexander
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