[PATCH v3] powerpc, pkey: make protection key 0 less special

[Michal Suchánek]

On Fri, 4 May 2018 14:45:07 -0700
Ram Pai <linuxram at us.ibm.com> wrote:

> On Fri, May 04, 2018 at 02:31:10PM -0700, Dave Hansen wrote:
> > On 05/04/2018 02:26 PM, Michal Suchánek wrote:  
> > > If it is not ok to change permissions of pkey 0 is it ok to free
> > > it?  
> > 
> > It's pretty much never OK to free it on x86 or ppc.  But, we're not
> > going to put code in to keep userspace from shooting itself in the
> > foot, at least on x86.  
> 
> and on powerpc aswell.

But once it's free it can be re-allocated. So you are moving the
special-casing from free code to code dealing with allocation.

If you want something like allocate_exec_only_pkey then the function
(either in kernel or in userspace) needs to make sure it is not
getting/requesting key 0 on powerpc.

Thanks

Michal