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

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Message-Id: <20160425140420.cf51815650e7237c7ed9ffbf@linux-foundation.org>
Date:	Mon, 25 Apr 2016 14:04:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	Laura Abbott <labbott@...hat.com>, Joe Perches <joe@...ches.com>,
	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] mm: SLAB freelist randomization

On Mon, 18 Apr 2016 12:52:30 -0700 Thomas Garnier <thgarnie@...gle.com> wrote:

> I agree, if we had a generic way to pass entropy across boots on all
> architecture that would be amazing. I will let the SLAB maintainers to
> decide on requiring CONFIG_ARCH_RANDOM or documenting it.

In our world, requiring that sort of attention from maintainers
requires a pretty active level of pinging, poking and harrassing ;)

I do think that if you stick with get_random_bytes_arch() then it need
a comment explaining why.

And I (still) don't think that get_random_bytes_arch() actually does
what you want - if CONFIG_ARCH_RANDOM isn't implemented then
get_random_bytes_arch() just fails.  IOW your statement "the arch
version that will fallback on get_random_bytes sub API in the worse
case" is a misconception?  There is no fallback.