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Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for slab sanitization

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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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[RFC][PATCH 0/7] Sanitization of slabs based on grsecurity/PaX Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  [RFC][PATCH 6/7] mm: Add Kconfig option for slab sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
    Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Mathias Krause <minipli@googlemail.com> - 2015-12-22 10:40 +0100
      Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 19:00 +0100
        Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Mathias Krause <minipli@googlemail.com> - 2015-12-22 19:40 +0100
          Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 20:20 +0100
          Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Christoph Lameter <cl@linux.com> - 2015-12-22 21:10 +0100
            Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Mathias Krause <minipli@googlemail.com> - 2015-12-22 21:10 +0100
    Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Dave Hansen <dave.hansen@intel.com> - 2015-12-22 16:00 +0100
      Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Christoph Lameter <cl@linux.com> - 2015-12-22 17:30 +0100
        Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Dave Hansen <dave.hansen@intel.com> - 2015-12-22 18:30 +0100
          Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Christoph Lameter <cl@linux.com> - 2015-12-22 19:10 +0100
            Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Dave Hansen <dave.hansen@intel.com> - 2015-12-22 19:20 +0100
              Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 20:20 +0100
                Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Dave Hansen <dave.hansen@intel.com> - 2015-12-22 20:40 +0100
        Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Christoph Lameter <cl@linux.com> - 2015-12-22 18:30 +0100
        Re: [kernel-hardening] [RFC][PATCH 6/7] mm: Add Kconfig option for  slab sanitization Dave Hansen <dave.hansen@intel.com> - 2015-12-22 18:30 +0100
  [RFC][PATCH 4/7] slob: Add support for sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  [RFC][PATCH 3/7] slab: Add support for sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  [RFC][PATCH 7/7] lkdtm: Add READ_AFTER_FREE test Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  [RFC][PATCH 5/7] mm: Mark several cases as SLAB_NO_SANITIZE Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  [RFC][PATCH 1/7] mm/slab_common.c: Add common support for slab saniziation Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
    Re: [RFC][PATCH 1/7] mm/slab_common.c: Add common support for slab  saniziation Vlastimil Babka <vbabka@suse.cz> - 2015-12-22 21:50 +0100
  [RFC][PATCH 2/7] slub: Add support for sanitization Laura Abbott <laura@labbott.name> - 2015-12-22 04:50 +0100
  Re: [RFC][PATCH 0/7] Sanitization of slabs based on grsecurity/PaX Christoph Lameter <cl@linux.com> - 2015-12-22 17:10 +0100
    Re: [kernel-hardening] Re: [RFC][PATCH 0/7] Sanitization of slabs  based on grsecurity/PaX Dave Hansen <dave.hansen@intel.com> - 2015-12-22 17:20 +0100
    Re: [kernel-hardening] Re: [RFC][PATCH 0/7] Sanitization of slabs  based on grsecurity/PaX Daniel Micay <danielmicay@gmail.com> - 2015-12-22 17:40 +0100
    Re: [RFC][PATCH 0/7] Sanitization of slabs based on grsecurity/PaX Laura Abbott <laura@labbott.name> - 2015-12-22 21:10 +0100

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