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Message-ID: <27cbe7f6-d372-f36c-d346-deb19b2cf39d@linux.com>
Date: Mon, 17 Aug 2020 23:34:17 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: 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
Subject: Re: [PATCH RFC 1/2] mm: Extract SLAB_QUARANTINE from KASAN
On 15.08.2020 21:54, 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 ;-)
Ok, I'll change that to "this feature is used by KASAN" :)
> 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.
>
> (feel free to edit this)
Ok, I see.
I'll start from high-level description and add low-level details at the end.
>> +struct qlist_node {
>> + struct qlist_node *next;
>> +};
>
> I appreciate this isn't new, but why do we have a new singly-linked-list
> abstraction being defined in this code?
I don't know for sure.
I suppose it is caused by SLAB/SLUB freelist implementation details (qlist_node
in kasan_free_meta is also used for the allocator freelist).
Best regards,
Alexander
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