Messages in this thread | | | Subject | Re: [PATCH 1/1] stackleak: Disable ftrace for stackleak.c | From | Alexander Popov <> | Date | Mon, 12 Nov 2018 19:51:00 +0300 |
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Hello Steven and Masami,
Thanks for your comments.
On 12.11.2018 5:50, Masami Hiramatsu wrote: > Hi Alexander and Steve, > > On Sun, 11 Nov 2018 20:53:51 -0500 > Steven Rostedt <rostedt@goodmis.org> wrote: > >> On Sun, 11 Nov 2018 13:19:45 +0300 >> Alexander Popov <alex.popov@linux.com> wrote: >> >>> On 11.11.2018 2:30, Steven Rostedt wrote: >>>> On Sun, 11 Nov 2018 01:05:30 +0300 >>>> Alexander Popov <alex.popov@linux.com> wrote: >>>> >>>>> The stackleak_erase() function is called on the trampoline stack at the >>>>> end of syscall. This stack is not big enough for ftrace operations, >>>>> e.g. it can be overflowed if we enable kprobe_events for stackleak_erase(). >>>> >>>> Is the issue with kprobes or with function tracing? Because this stops >>>> function tracing which I only want disabled if function tracing itself >>>> is an issue, not for other things that may use the function tracing >>>> infrastructure. >>> >>> Hello Steven, >>> >>> I believe that stackleak erasing is not compatible with function tracing itself. >>> That's what the kernel testing robot has hit: >>> https://www.openwall.com/lists/kernel-hardening/2018/11/09/1 >>> >>> I used kprobe_events just to reproduce the problem: >>> https://www.openwall.com/lists/kernel-hardening/2018/11/09/4 >> >> Have you tried adding a "notrace" to stackleak_erase()? >> >> Not tracing the entire file is a bit of overkill. There's no reason >> ftrace can't trace stack_erasing_sysctl() or perhaps even >> stackleak_track_stack() as that may be very interesting to trace.
Yes, thank you. It's much better.
> I think it is not enough for stopping kprobes. If you want to stop the kprobes > (int3 version) on stackleak_erase(), you should use NOKPROBE_SYMBOL(stackleak_erase), > since kprobes can work without ftrace.
Thanks!
I learned how to use kprobes without ftrace and managed to reproduce the problem as well (I modified kprobe_example.c and kretprobe_example.c). NOKPROBE_SYMBOL() allowed to avoid it.
I'll send the patch soon.
By the way, are there any other tracing/instrumentation mechanisms that should be disabled?
Best regards, Alexander
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