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

Pekka Enberg
2009-05-30T07:57:10Z

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:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=00fcf2cb6f6bb421851c3ba062c0a36760ea6e53

Can we now get to the part where you explain how it's broken because I
obviously "ignored how SLAB/SLUB works"?

Thanks!

Pekka