Re: pkeys on POWER: Access rights not reset on execve

[Florian Weimer <fweimer@redhat.com>]

On 06/08/2018 02:54 PM, Michal Suchánek wrote:
> On Fri, 8 Jun 2018 12:44:53 +0200
> Florian Weimer <fweimer@redhat.com> wrote:
> 
>> On 06/08/2018 12:15 PM, Michal Suchánek wrote:
>>> On Fri, 8 Jun 2018 07:53:51 +0200
>>> Florian Weimer <fweimer@redhat.com> wrote:
>>>    
>>>> On 06/08/2018 04:34 AM, Ram Pai wrote:
>>>>>>
>>>>>> So the remaining question at this point is whether the Intel
>>>>>> behavior (default-deny instead of default-allow) is preferable.
>>>>>
>>>>> Florian, remind me what behavior needs to fixed?
>>>>
>>>> See the other thread.  The Intel register equivalent to the AMR by
>>>> default disallows access to yet-unallocated keys, so that threads
>>>> which are created before key allocation do not magically gain
>>>> access to a key allocated by another thread.
>>>>   
>>>
>>> That does not make any sense. The threads share the address space so
>>> they should also share the keys.
>>>
>>> Or in other words the keys are supposed to be acceleration of
>>> mprotect() so if mprotect() magically gives access to threads that
>>> did not call it so should pkey functions. If they cannot do that
>>> then they fail the primary purpose.
>>
>> That's not how protection keys work.  The access rights are
>> thread-specific, so that you can change them locally, without
>> synchronization and expensive inter-node communication.
>>
> 
> And the association of a key with part of the address space is
> thread-local as well?

No, that part is still per-process.

Florian