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

[Pekka Enberg]

Hi Alan,

On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
>> It's pretty damn obvious that Larry's patches have a much bigger
>> performance impact than using kzfree() for selected parts of the
>> kernel. So yes, I do expect him to benchmark and demonstrate that
>> kzfree() has _performance problems_ before we can look into merging
>> his patches.
>
> We seem to be muddling up multiple things here which is not helpful.

Yup.

On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> There are three things going on
>
> #1 Is ksize() buggy ?

No, there's nothing wrong with ksize() I am aware of. Yes, Larry has
been saying it is but hasn't provided any evidence so far.

On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> #2 Using kzfree() to clear specific bits of memory (and I question the
> kzfree implementation as it seems ksize can return numbers much much
> bigger than the allocated space you need to clear - correct but oversize)
> or using other flags. I'd favour kzfree personally (and fixing it to work
> properly)

Well, yes, that's what kzfree() needs to do given the current API. I
am not sure why you think it's a problem, though. Adding a size
argument to the function will make it more error prone.

On Sun, May 31, 2009 at 2:10 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> #3 People wanting to be able to select for more security *irrespective*
> of performance cost. Which is no different to SELinux for example.

Yeah, as I said before, I really don't have any objections to this. I
just think nobody is going to enable it so memset() or kzfree() in
relevant places is probably a good idea.

                                   Pekka
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