linux-kernel - Re: [PATCH v2] mm: SLAB freelist randomization

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Message-ID: <CAJcbSZE6srG0zgb5Jt8WF9RiTewhn9PEU_3mbzHw2jt3HKdRHg@mail.gmail.com>
Date:	Mon, 25 Apr 2016 14:43:58 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Kees Cook <keescook@...omium.org>,
	Greg Thelen <gthelen@...gle.com>,
	Laura Abbott <labbott@...oraproject.org>,
	kernel-hardening@...ts.openwall.com,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] mm: SLAB freelist randomization

On Mon, Apr 25, 2016 at 2:38 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 25 Apr 2016 14:14:33 -0700 Thomas Garnier <thgarnie@...gle.com> wrote:
>
>> >>> +     /* Get best entropy at this stage */
>> >>> +     get_random_bytes_arch(&seed, sizeof(seed));
>> >>
>> >> See concerns in other email - isn't this a no-op if CONFIG_ARCH_RANDOM=n?
>> >>
>>
>> The arch_* functions will return 0 which will break the loop in
>> get_random_bytes_arch and make it uses extract_entropy (as does
>> get_random_bytes).
>> (cf http://lxr.free-electrons.com/source/drivers/char/random.c#L1335)
>>
>
> oop, sorry, I misread the code.
>
> (and the get_random_bytes_arch() comment "This function will use the
> architecture-specific hardware random number generator if it is
> available" is misleading, so there)

No problem, better double check it. I agree it is misleading.

Thomas