Re: [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces

Josh Poimboeuf
2016-12-20T21:21:36Z

On Tue, Dec 20, 2016 at 10:39:16AM +0100, Petr Mladek wrote:
> On Mon 2016-12-19 11:25:49, Josh Poimboeuf wrote:
> > 3) probably some kind of runtime NMI stack checking feature to
> > complement objtool, along with a lot of burn time to ensure there are
> > no issues, particularly in entry code
>
> Could you please provide more details about this NMI stack checking?
> What is it supposed to protect that objtool could not?
> Will it run regularly or will it be just a random check?

save_stack_trace_tsk_reliable(current) would be called periodically from
an NMI handler, and a warning would be printed if it ever doesn't reach
the "end" of the stack (i.e., user-mode pt_regs). Due to the
performance impact it would probably only be a debug option.

It would verify the special hand-coded areas which objtool isn't smart
enough to understand, like entry code, ftrace, kprobes, bpf. It would
also make sure that objtool itself didn't missing anything.

--
Josh