On Thu, Apr 20, 2017 at 05:22:36PM -0400, Steven Rostedt (VMware) wrote: > From: Steven Rostedt (VMware) <rost...@goodmis.org> > > Fengguang Wu's zero day bot triggered a stack unwinder dump. This can > be easily triggered when CONFIG_FRAME_POINTERS is enabled and -mfentry > is in use on x86_32. > > ># cd /sys/kernel/debug/tracing > ># echo 'p:schedule schedule' > kprobe_events > ># echo stacktrace > events/kprobes/schedule/trigger > > This is because the code that implemented fentry in the > ftrace_regs_caller tried to use the least amount of #ifdefs, and > modified ebp when CC_USE_FENTRY was defined to point to the parent ip > as it does when CC_USE_FENTRY is not defined. But when > CONFIG_FRAME_POINTERS is set, it corrupts the ebp register for this > frame while doing the tracing. > > NOTE, it does not corrupt ebp in any other way. It is just a bad > frame pointer when calling into the tracing infrastructure. The original > ebp is restored before returning from the fentry call. But if a stack > trace is performed inside the tracing, the unwinder will notice the bad > ebp. > > Instead of toying with ebp with CC_USING_FENTRY, just slap the parent > ip into the second parameter (%edx), and have an #else that does it the > original way. > > The unwinder will unfortunately miss the function being traced, as the > stack frame is not set up yet for it, as it is for x86_64. But fixing > that is a bit more complex and did not work before anyway. > > This has been tested with and without FRAME_POINTERS being set while > using -mfentry, as well as using an older compiler that uses mcount. > > Reported-by: kernel test robot <fengguang...@intel.com> > Analyzed-by: Josh Poimboeuf <jpoim...@redhat.com> > Link: https://lists.01.org/pipermail/lkp/2017-April/006165.html > Fixes: 644e0e8dc76b ("x86/ftrace: Add -mfentry support to x86_32 with > DYNAMIC_FTRACE set") > Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
It's actually CONFIG_FRAME_POINTER (no 'S'). Otherwise, Reviewed-by: Josh Poimboeuf <jpoim...@redhat.com> -- Josh
