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

On Sat, May 05, 2018 at 02:39:56PM +0200, Michal Suchánek wrote:

On Fri, 4 May 2018 14:45:07 -0700
Ram Pai [off-list ref] wrote:

quoted

On Fri, May 04, 2018 at 02:31:10PM -0700, Dave Hansen wrote:

quoted

On 05/04/2018 02:26 PM, Michal Suchánek wrote:  

quoted

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.

Actually if an application frees key-0, it has potentially opened up a
can-of-worms. It could step on anything that explodes. 

Its choice between imposing policies on an application v/s freeing it up
to choose its own policy. I think the kernel should impose some form of
mild-policy. But others think there should be none.

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.

Yes. makes sense. I will put in some checks towards that.


Thanks,
RP

Thanks

Michal

-- 
Ram Pai