On Tue, Dec 20, 2016 at 10:39:16AM +0100, Petr Mladek wrote:

On Mon 2016-12-19 11:25:49, Josh Poimboeuf wrote:

quoted

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