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

["Michal Suchánek" <msuchanek@suse.de>]

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?

Thanks

Michal