Re: [PATCH v3 18/39] x86/ibt,ftrace: Make function-graph play nice

Josh Poimboeuf
2022-03-04T21:03:46Z

On Fri, Mar 04, 2022 at 08:48:53PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 04, 2022 at 09:51:54AM -0800, Josh Poimboeuf wrote:
> > On Thu, Mar 03, 2022 at 12:23:39PM +0100, Peter Zijlstra wrote:
> > > +
> > > + addq $16, %rsp
> > > + ANNOTATE_INTRA_FUNCTION_CALL
> > > + call .Ldo_rop
> > > + int3
> > > +.Ldo_rop:
> > > + mov %rdi, (%rsp)
> > > + UNWIND_HINT_FUNC
> > > + RET
> >
> > Why the int3?
>
> Speculation trap :-) Either I'm too paranoid or not paranoid enough; but
> without it it's just too close to a retpoline and it doesn't feel right.

Um, it *is* a retpoline :-)

Can you just use the RETPOLINE macro? Along with a comment stating why
it can't just do a JMP_NOSPEC?

--
Josh