linux-kernel - Re: [PATCH RFC 1/2] mm: Extract SLAB

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Date:   Sun, 16 Aug 2020 21:59:30 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexander Popov <alex.popov@...ux.com>,
        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 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?

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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