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Date: Tue, 9 Apr 2019 10:55:27 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Laura Abbott <labbott@...hat.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	linux-security-module <linux-security-module@...r.kernel.org>, 
	linux-kbuild <linux-kbuild@...r.kernel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Kostya Serebryany <kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 2/2] initmem: introduce CONFIG_INIT_ALL_HEAP

On Mon, Apr 8, 2019 at 7:14 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Apr 8, 2019 at 9:43 AM Laura Abbott <labbott@...hat.com> wrote:
> > I've looked at doing something similar in the past (failing to find
> > the thread this morning...) and while this will work, it has pretty
> > serious performance issues. It's not actually the poisoning which
> > is expensive but that turning on debugging removes the cpu slab
> > which has significant performance penalties.
> >
> > I'd rather go back to the proposal of just poisoning the slab
> > at alloc/free without using SLAB_POISON.
>
> I still agree this would make the most sense. Fundamentally it's not a
> debugging feature.
Wasn't it you who suggested using SLAB_POISON in the first round of comments? :)

I actually have a working implementation that piggybacks on existing
__GFP_ZERO code to initialize page_alloc() and SLUB allocations:
https://github.com/google/kmsan/commit/4907af529ad525378a0728435c96d3812f71e594
https://github.com/google/kmsan/commit/69618a9668bcf27700cc5da42eebf8ab50d1f56a

I'd better cook a patch based on that.

There's also some overhead when allocations are initialized twice (in
page_alloc() and kmalloc()) or thrice (page_alloc(), kmalloc() and
e.g. sock_alloc_send_pskb())
We can introduce another GFP flag explicitly telling the allocator to
not initialize the memory chunk if we know it'll be initialized by a
higher level allocator
(something along the lines of
https://github.com/google/kmsan/commit/4fc8cff79d868c29688c8a4186e504fda362f6fd)
> --
> Kees Cook



-- 
Alexander Potapenko
Software Engineer

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