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Date: Thu, 18 Apr 2019 18:43:27 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, 
	Dmitriy Vyukov <dvyukov@...gle.com>, Kees Cook <keescook@...omium.org>, 
	Laura Abbott <labbott@...hat.com>, Linux Memory Management List <linux-mm@...ck.org>, 
	linux-security-module <linux-security-module@...r.kernel.org>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 1/3] mm: security: introduce the init_allocations=1 boot option

On Thu, Apr 18, 2019 at 6:35 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 4/18/19 8:42 AM, Alexander Potapenko wrote:
> > This option adds the possibility to initialize newly allocated pages and
> > heap objects with zeroes. This is needed to prevent possible information
> > leaks and make the control-flow bugs that depend on uninitialized values
> > more deterministic.
>
> Isn't it better to do this at free time rather than allocation time?  If
> doing it at free, you can't even have information leaks for pages that
> are in the allocator.
I should have mentioned this in the patch description, as this
question is being asked every time I send a patch :)
If we want to avoid double initialization and take advantage of
__GFP_NOINIT (see the second and third patches in the series) we need
to do initialize the memory at allocation time, because free() and
free_pages() don't accept GFP flags.



-- 
Alexander Potapenko
Software Engineer

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