Re: pkeys: Reserve PKEY_DISABLE_READ

[Ram Pai <linuxram@us.ibm.com>]

On Thu, Nov 08, 2018 at 06:37:41PM +0100, Florian Weimer wrote:
> * Dave Hansen:
> 
> > On 11/8/18 7:01 AM, Florian Weimer wrote:
> >> Ideally, PKEY_DISABLE_READ | PKEY_DISABLE_WRITE and PKEY_DISABLE_READ |
> >> PKEY_DISABLE_ACCESS would be treated as PKEY_DISABLE_ACCESS both, and a
> >> line PKEY_DISABLE_READ would result in an EINVAL failure.
> >
> > Sounds reasonable to me.
> >
> > I don't see any urgency to do this right now.  It could easily go in
> > alongside the ppc patches when those get merged.
> 
> POWER support has already been merged, so we need to do something here
> now, before I can complete the userspace side.
> 
> > The only thing I'd suggest is that we make it something slightly
> > higher than 0x4.  It'll make the code easier to deal with in the
> > kernel if we have the ABI and the hardware mirror each other, and if
> > we pick 0x4 in the ABI for PKEY_DISABLE_READ, it might get messy if
> > the harware choose 0x4 for PKEY_DISABLE_EXECUTE or something.
> > 
> > So, let's make it 0x80 or something on x86 at least.
> 
> I don't have a problem with that if that's what it takes.
> 
> > Also, I'll be happy to review and ack the patch to do this, but I'd
> > expect the ppc guys (hi Ram!) to actually put it together.
> 
> Ram, do you want to write a patch?


Florian,

	I can. But I am struggling to understand the requirement. Why is
	this needed?  Are we proposing a enhancement to the sys_pkey_alloc(),
	to be able to allocate keys that are initialied to disable-read
	only?

RP

> 
> I'll promise I finish the glibc support for this. 8-)
> 
> Thanks,
> Florian

-- 
Ram Pai