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

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Date:	Mon, 18 Apr 2016 08:59:57 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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

I will send the next version today. Note that I get_random_bytes_arch
is used because at that stage we have 0 bits of entropy. It seemed
like a better idea to use the arch version that will fallback on
get_random_bytes sub API in the worse case.

On Fri, Apr 15, 2016 at 3:47 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
> Thanks for the comments. I will address them in a v2 early next week.
>
> If anyone has other comments, please let me know.
>
> Thomas
>
> On Fri, Apr 15, 2016 at 3:26 PM, Joe Perches <joe@...ches.com> wrote:
>> On Fri, 2016-04-15 at 15:00 -0700, Andrew Morton wrote:
>>> On Fri, 15 Apr 2016 10:25:59 -0700 Thomas Garnier <thgarnie@...gle.com> wrote:
>>> > Provide an optional config (CONFIG_FREELIST_RANDOM) to randomize the
>>> > SLAB freelist. The list is randomized during initialization of a new set
>>> > of pages. The order on different freelist sizes is pre-computed at boot
>>> > for performance. This security feature reduces the predictability of the
>>> > kernel SLAB allocator against heap overflows rendering attacks much less
>>> > stable.
>>
>> trivia:
>>
>>> > @@ -1229,6 +1229,61 @@ static void __init set_up_node(struct kmem_cache *cachep, int index)
>> []
>>> > + */
>>> > +static freelist_idx_t master_list_2[2];
>>> > +static freelist_idx_t master_list_4[4];
>>> > +static freelist_idx_t master_list_8[8];
>>> > +static freelist_idx_t master_list_16[16];
>>> > +static freelist_idx_t master_list_32[32];
>>> > +static freelist_idx_t master_list_64[64];
>>> > +static freelist_idx_t master_list_128[128];
>>> > +static freelist_idx_t master_list_256[256];
>>> > +static struct m_list {
>>> > +   size_t count;
>>> > +   freelist_idx_t *list;
>>> > +} master_lists[] = {
>>> > +   { ARRAY_SIZE(master_list_2), master_list_2 },
>>> > +   { ARRAY_SIZE(master_list_4), master_list_4 },
>>> > +   { ARRAY_SIZE(master_list_8), master_list_8 },
>>> > +   { ARRAY_SIZE(master_list_16), master_list_16 },
>>> > +   { ARRAY_SIZE(master_list_32), master_list_32 },
>>> > +   { ARRAY_SIZE(master_list_64), master_list_64 },
>>> > +   { ARRAY_SIZE(master_list_128), master_list_128 },
>>> > +   { ARRAY_SIZE(master_list_256), master_list_256 },
>>> > +};
>>
>> static const struct m_list?
>>