Re: [PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change signal semantics

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

On Mon, May 14, 2018 at 02:01:23PM +0200, Florian Weimer wrote:
> On 05/09/2018 04:41 PM, Andy Lutomirski wrote:
> >Hmm.  I can get on board with the idea that fork() / clone() /
> >pthread_create() are all just special cases of the idea that the thread
> >that*calls*  them should have the right pkey values, and the latter is
> >already busted given our inability to asynchronously propagate the new mode
> >in pkey_alloc().  So let's so PKEY_ALLOC_SETSIGNAL as a starting point.
> 
> Ram, any suggestions for implementing this on POWER?

I suspect the changes will go in 
restore_user_regs() and save_user_regs().  These are the functions
that save and restore register state before entry and exit into/from
a signal handler.

> 
> >One thing we could do, though: the current initual state on process
> >creation is all access blocked on all keys.  We could change it so that
> >half the keys are fully blocked and half are read-only.  Then we could add
> >a PKEY_ALLOC_STRICT or similar that allocates a key with the correct
> >initial state*and*  does the setsignal thing.  If there are no keys left
> >with the correct initial state, then it fails.
> 
> The initial PKRU value can currently be configured by the system
> administrator.  I fear this approach has too many moving parts to be
> viable.

Sounds like on x86  keys can go active in signal-handler 
without any explicit allocation request by the application.  This is not
the case on power. Is that API requirement? Hope not.

RP