Re: pkeys: Support setting access rights for signal handlers

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

On Mon, Dec 11, 2017 at 08:13:12AM -0800, Dave Hansen wrote:
> On 12/09/2017 10:42 PM, Florian Weimer wrote:
> >> My only nit with this is whether it is the *right* interface.  The 
> >> signal vs. XSAVE state thing is pretty x86 specific and I doubt
> >> that this will be the last feature that we encounter that needs
> >> special signal behavior.
> > 
> > The interface is not specific to XSAVE.  To generic code, only the
> > two signal mask manipulation functions are exposed.  And I expect
> > that we're going to need that for other (non-x86) implementations
> > because they will have the same issue because the signal handler
> > behavior will be identical.
> 
> Let's check with the other implementation...
> 
> Ram, this is a question about the signal handler behavior on POWER.  I
> thought you ended up having different behavior in signal handlers than x86.

On POWER, the value of the pkey_read() i.e contents the AMR
register(pkru equivalent), is always the same regardless of its
context; signal handler or not.

In other words, the permission of any allocated key will not
reset in a signal handler context.

I was not aware that x86 would reset the key permissions in signal
handler.  I think, the proposed behavior for PKEY_ALLOC_SETSIGNAL should
actually be the default behavior.


RP