Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for
slab sanitization
[Posted December 23, 2015 by jake]
| From: |
| Laura Abbott <laura-AT-labbott.name> |
| To: |
| Dave Hansen <dave.hansen-AT-intel.com>, Christoph Lameter <cl-AT-linux.com> |
| Subject: |
| Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for slab sanitization |
| Date: |
| Tue, 22 Dec 2015 11:13:15 -0800 |
| Message-ID: |
| <5679A0CB.3060707@labbott.name> |
| Cc: |
| kernel-hardening-AT-lists.openwall.com, Pekka Enberg <penberg-AT-kernel.org>, David Rientjes <rientjes-AT-google.com>, Joonsoo Kim <iamjoonsoo.kim-AT-lge.com>, Andrew Morton <akpm-AT-linux-foundation.org>, linux-mm-AT-kvack.org, linux-kernel-AT-vger.kernel.org, Kees Cook <keescook-AT-chromium.org> |
| Archive‑link: | |
Article |
On 12/22/15 10:19 AM, Dave Hansen wrote:
> On 12/22/2015 10:08 AM, Christoph Lameter wrote:
>> On Tue, 22 Dec 2015, Dave Hansen wrote:
>>>> Why would you use zeros? The point is just to clear the information right?
>>>> The regular poisoning does that.
>>>
>>> It then allows you to avoid the zeroing at allocation time.
>>
>> Well much of the code is expecting a zeroed object from the allocator and
>> its zeroed at that time. Zeroing makes the object cache hot which is an
>> important performance aspect.
>
> Yes, modifying this behavior has a performance impact. It absolutely
> needs to be evaluated, and I wouldn't want to speculate too much on how
> good or bad any of the choices are.
>
> Just to reiterate, I think we have 3 real choices here:
>
> 1. Zero at alloc, only when __GFP_ZERO
> (behavior today)
> 2. Poison at free, also Zero at alloc (when __GFP_ZERO)
> (this patch's proposed behavior, also what current poisoning does,
> doubles writes)
> 3. Zero at free, *don't* Zero at alloc (when __GFP_ZERO)
> (what I'm suggesting, possibly less perf impact vs. #2)
>
>
poisoning with non-zero memory makes it easier to determine that the error
came from accessing the sanitized memory vs. some other case. I don't think
the feature would be as strong if the memory was only zeroed vs. some other
data value.
Thanks,
Laura
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