Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Josh Poimboeuf
2018-11-26T16:44:40Z

On Mon, Nov 26, 2018 at 05:39:23PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 26, 2018 at 05:11:05PM +0100, Ard Biesheuvel wrote:
> > On Mon, 26 Nov 2018 at 17:08, Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote:
> > > > +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> > > > +void arch_static_call_defuse_tramp(void *site, void *tramp)
> > > > +{
> > > > + unsigned short opcode = INSN_UD2;
> > > > +
> > > > + mutex_lock(&text_mutex);
> > > > + text_poke((void *)tramp, &opcode, 2);
> > > > + mutex_unlock(&text_mutex);
> > > > +}
> > > > +#endif
> > >
> > > I would rather think that makes the trampoline _more_ dangerous, rather
> > > than less so.
> > >
> > > My dictionary sayeth:
> > >
> > > defuse: verb
> > >
> > > - remove the fuse from (an explosive device) in order to prevent it
> > > from exploding.
> > >
> > > - make (a situation) less tense or dangerous
> > >
> > > patching in an UD2 seems to do the exact opposite.
> >
> > That is my fault.
> >
> > The original name was 'poison' iirc, but on arm64, we need to retain
> > the trampoline for cases where the direct branch is out of range, and
> > so poisoning is semantically inaccurate.
> >
> > But since you opened your dictionary anyway, any better suggestions? :-)
>
> I was leaning towards: "prime", but I'm not entirely sure that works
> with your case.

Maybe we should just go back to "poison", along with a comment that it
will not necessarily be poisoned for all arches. I think "poison" at
least describes the intent, if not always the implementation.

--
Josh