linux-kernel - Re: [PATCH RFC v2 0/6] Break heap spraying needed for exploiting use-after-free

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Date:   Tue, 6 Oct 2020 08:35:50 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Kees Cook <keescook@...omium.org>
cc:     Matthew Wilcox <willy@...radead.org>, Jann Horn <jannh@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Will Deacon <will@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.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>,
        Daniel Micay <danielmicay@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Pavel Machek <pavel@...x.de>,
        Valentin Schneider <valentin.schneider@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        kernel list <linux-kernel@...r.kernel.org>, notify@...nel.org
Subject: Re: [PATCH RFC v2 0/6] Break heap spraying needed for exploiting
 use-after-free


On Mon, 5 Oct 2020, Kees Cook wrote:

> > TYPESAFE_BY_RCU, but if forcing that on by default would enhance security
> > by a measurable amount, it wouldn't be a terribly hard sell ...
>
> Isn't the "easy" version of this already controlled by slab_merge? (i.e.
> do not share same-sized/flagged kmem_caches between different caches)

Right.

> The large trouble are the kmalloc caches, which don't have types
> associated with them. Having implicit kmem caches based on the type
> being allocated there would need some pretty extensive plumbing, I
> think?

Actually typifying those accesses may get rid of a lot of kmalloc
allocations and could help to ease the management and control of objects.

It may be a big task though given the ubiquity of kmalloc and the need to
create a massive amount of new slab caches. This is going to reduce the
cache hit rate significantly.