On Wed, May 16, 2018 at 01:37:46PM -0700, Andy Lutomirski wrote: > On Wed, May 16, 2018 at 1:35 PM Ram Pai <linuxram@xxxxxxxxxx> wrote: > > > On Tue, May 08, 2018 at 02:40:46PM +0200, Florian Weimer wrote: > > > On 05/08/2018 04:49 AM, Andy Lutomirski wrote: > > > >On Mon, May 7, 2018 at 2:48 AM Florian Weimer <fweimer@xxxxxxxxxx> > wrote: > > > > > > > >>On 05/03/2018 06:05 AM, Andy Lutomirski wrote: > > > >>>On Wed, May 2, 2018 at 7:11 PM Ram Pai <linuxram@xxxxxxxxxx> wrote: > > > >>> > > > >>>>On Wed, May 02, 2018 at 09:23:49PM +0000, Andy Lutomirski wrote: > > > >>>>> > > > >>>>>>If I recall correctly, the POWER maintainer did express a strong > > > >>>desire > > > >>>>>>back then for (what is, I believe) their current semantics, which > my > > > >>>>>>PKEY_ALLOC_SIGNALINHERIT patch implements for x86, too. > > > >>>>> > > > >>>>>Ram, I really really don't like the POWER semantics. Can you give > > > >some > > > >>>>>justification for them? Does POWER at least have an atomic way for > > > >>>>>userspace to modify just the key it wants to modify or, even > better, > > > >>>>>special load and store instructions to use alternate keys? > > > >>> > > > >>>>I wouldn't call it POWER semantics. The way I implemented it on > power > > > >>>>lead to the semantics, given that nothing was explicitly stated > > > >>>>about how the semantics should work within a signal handler. > > > >>> > > > >>>I think that this is further evidence that we should introduce a new > > > >>>pkey_alloc() mode and deprecate the old. To the extent possible, > this > > > >>>thing should work the same way on x86 and POWER. > > > > > > > >>Do you propose to change POWER or to change x86? > > > > > > > >Sorry for being slow to reply. I propose to introduce a new > > > >PKEY_ALLOC_something variant on x86 and POWER and to make the behavior > > > >match on both. > > > > > > So basically implement PKEY_ALLOC_SETSIGNAL for POWER, and keep the > > > existing (different) behavior without the flag? > > > > > > Ram, would you be okay with that? Could you give me a hand if > > > necessary? (I assume we have silicon in-house because it's a > > > long-standing feature of the POWER platform which was simply dormant > > > on Linux until now.) > > > Yes. I can help you with that. > > > So let me see if I understand the overall idea. > > > Application can allocate new keys through a new syscall > > sys_pkey_alloc_1(flags, init_val, sig_init_val) > > > 'sig_init_val' is the permission-state of the key in signal context. > > > The kernel will set the permission of each keys to their > > corresponding values when entering the signal handler and revert > > on return from the signal handler. > > > just like init_val, sig_init_val also percolates to children threads. > > > I was imagining it would be just pkey_alloc(SOME_NEW_FLAG, init_val); and > the init val would be used for the current thread and for signal handlers. what would change the key-permission-values enforced in signal-handler context? Or can it never be changed, ones set through sys_pkey_alloc()? I suppose key-permission-values change done in non-signal-handler context, will not apply to those in signal-handler context. Can the signal handler change the key-permission-values from the signal-handler context? RP
