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

[Florian Weimer]

On 03/09/2018 09:00 PM, Ram Pai wrote:
> On Fri, Mar 09, 2018 at 12:04:49PM +0100, Florian Weimer wrote:
> > On 03/09/2018 09:12 AM, Ram Pai 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.
> >
> > mprotect without a key does not necessarily use key 0, e.g. if
> > protection keys are used to emulate page protection flag combination
> > which is not directly supported by the hardware.
> >
> > Therefore, it seems to me that filtering out non-allocated keys is
> > the right thing to do.
>
> I am not sure, what you mean. Do you agree with the patch or otherwise?

I think it's inconsistent to make key 0 allocated, but not the key which 
is used for PROT_EXEC emulation, which is still reserved.  Even if you 
change the key 0 behavior, it is still not possible to emulate mprotect 
behavior faithfully with an allocated key.

Thanks,
Florian