Re: [PATCH -tip v4 10/12] x86/kprobes: Push a fake return address at kretprobe_trampoline

Josh Poimboeuf
2021-03-24T16:01:43Z

On Wed, Mar 24, 2021 at 10:40:58AM +0900, Masami Hiramatsu wrote:
> On Tue, 23 Mar 2021 23:30:07 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Mon, Mar 22, 2021 at 03:41:40PM +0900, Masami Hiramatsu wrote:
> > > ".global kretprobe_trampoline\n"
> > > ".type kretprobe_trampoline, @function\n"
> > > "kretprobe_trampoline:\n"
> > > #ifdef CONFIG_X86_64
> >
> > So what happens if we get an NMI here? That is, after the RET but before
> > the push? Then our IP points into the trampoline but we've not done that
> > push yet.
>
> Not only NMI, but also interrupts can happen. There is no cli/sti here.
>
> Anyway, thanks for pointing!
> I think in UNWIND_HINT_TYPE_REGS and UNWIND_HINT_TYPE_REGS_PARTIAL cases
> ORC unwinder also has to check the state->ip and if it is kretprobe_trampoline,
> it should be recovered.
> What about this?

I think the REGS and REGS_PARTIAL cases can also be affected by function
graph tracing. So should they use the generic unwind_recover_ret_addr()
instead of unwind_recover_kretprobe()?

--
Josh