pkeys on POWER: Access rights not reset on execve

[Florian Weimer]

On 05/19/2018 03:50 AM, Andy Lutomirski wrote:
> Now another thread calls pkey_alloc(), so UAMR is asynchronously changed,
> and the thread will write zero to the relevant AMR bits.  If I understand
> correctly, this means that the decision to mask off unallocated keys via
> UAMR effectively forces the initial value of newly-allocated keys in other
> threads in the allocating process to be zero, whatever zero means.  (I
> didn't get far enough in the POWER docs to figure out what zero means.)  So

(Note that this belongs on the other thread, here I originally wanted to 
talk about the lack of reset of AMR to the default value on execve.)

I don't think UAMOR is updated asynchronously.  On pkey_alloc, it is 
only changed for the current thread, and future threads launched from 
it.  Existing threads are unaffected.  This still results in a 
programming model which is substantially different from x86.

> I don't think you're doing anyone any favors by making UAMR dynamic.

This is still true, I think.

Thanks,
Florian