Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

[Balbir Singh]

On Fri, Mar 9, 2018 at 7:12 PM, Ram Pai <linuxram@xxxxxxxxxx> wrote:
> Once an address range is associated with an allocated pkey, it cannot be
> reverted back to key-0. There is no valid reason for the above behavior.  On
> the contrary applications need the ability to do so.
>
> The patch relaxes the restriction.

I looked at the code and my observation was going to be that we need
to change mm_pkey_is_allocated. I still fail to understand what
happens if pkey 0 is reserved? What is the default key is it the first
available key? Assuming 0 is the default key may work and seems to
work, but I am sure its mostly by accident. It would be nice, if we
could have  a notion of the default key. I don't like the special
meaning given to key 0 here. Remember on powerpc if 0 is reserved and
UAMOR/AMOR does not allow modification because it's reserved, setting
0 will still fail

Balbir