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

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Message-Id: <20160425143850.b767ca9602fc1be9e13462a5@linux-foundation.org>
Date:	Mon, 25 Apr 2016 14:38:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Thomas Garnier <thgarnie@...gle.com>
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, 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)