Re: [patch 0/5] Support for sanitization flag in low-level pageallocator

From: Ingo Molnar
Date: Sat May 30 2009 - 13:39:45 EST

* Pekka Enberg <penberg@xxxxxxxxxxxxxx> wrote:

> Hi Larry,
> On 10:35 Sat 30 May, Pekka Enberg wrote:
>>> The GFP_SENSITIVE flag looks like a big hammer that we don't really
>>> need IMHO. It seems to me that most of the actual call-sites (crypto
>>> code, wireless keys, etc.) should probably just use kzfree()
>>> unconditionally to make sure we don't leak sensitive data. I did not
>>> look too closely but I don't think any of the sensitive kfree() calls
>>> are in fastpaths so the performance impact is negligible.
> Larry H. wrote:
>> That's hopeless, and kzfree is broken. Like I said in my earlier reply,
>> please test that yourself to see the results. Whoever wrote that ignored
>> how SLAB/SLUB work and if kzfree had been used somewhere in the kernel
>> before, it should have been noticed long time ago.
> An open-coded version of kzfree was being used in the kernel:
> Can we now get to the part where you explain how it's broken
> because I obviously "ignored how SLAB/SLUB works"?

Yeah, kzfree() sounds like the right approach for all places that
know it for sure that they dont want information to persist.

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