[PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change signal semantics
Ram Pai
linuxram at us.ibm.com
Thu May 17 06:52:44 AEST 2018
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
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