Re: [PATCH 5/8] x86, pkeys: allocation/free syscalls

From: Michael Kerrisk (man-pages)
Date: Thu Jun 02 2016 - 20:26:28 EST

On 06/01/2016 07:17 PM, Dave Hansen wrote:
> On 06/01/2016 05:11 PM, Michael Kerrisk (man-pages) wrote:
>>>>>> If I read this right, it doesn't actually remove any pkey restrictions
>>>>>> that may have been applied while the key was allocated. So there could be
>>>>>> pages with that key assigned that might do surprising things if the key is
>>>>>> reallocated for another use later, right? Is that how the API is intended
>>>>>> to work?
>>>> Yeah, that's how it works.
>>>> It's not ideal. It would be _best_ if we during mm_pkey_free(), we
>>>> ensured that no VMAs under that mm have that vma_pkey() set. But, that
>>>> search would be potentially expensive (a walk over all VMAs), or would
>>>> force us to keep a data structure with a count of all the VMAs with a
>>>> given key.
>>>> I should probably discuss this behavior in the manpages and address it
>> s/probably//
>> And, did I miss it. Was there an updated man-pages patch in the latest
>> series? I did not notice it.
> There have been to changes to the patches that warranted updating the
> manpages until now. I'll send the update immediately.

Do those updated pages include discussion of the point noted above?
I could not see it mentioned there.

Just by the way, the above behavior seems to offer possibilities
for users to shoot themselves in the foot, in a way that has security
implications. (Or do I misunderstand?)



Michael Kerrisk
Linux man-pages maintainer;
Linux/UNIX System Programming Training: