On Thu, 26 Jul 2018 14:53:27 +0900 Masami Hiramatsu <mhira...@kernel.org> wrote:
> Prohibit kprobe-events probing on notrace function. > Since probing on the notrace function can cause recursive > event call. In most case those are just skipped, but > in some case it falls into infinit recursive call. > > This protection can be disabled by the kconfig > CONFIG_KPROBE_EVENTS_ON_NOTRACE=y, but it is highly > recommended to keep it "n" for normal kernel. > > Signed-off-by: Masami Hiramatsu <mhira...@kernel.org> > Tested-by: Francis Deslauriers <francis.deslauri...@efficios.com> > --- > Changes from v1 > - Add CONFIG_KPROBE_EVENTS_ON_NOTRACE kconfig for knocking down > the protection. > --- > kernel/trace/Kconfig | 18 ++++++++++++++++++ > kernel/trace/trace_kprobe.c | 23 +++++++++++++++++++++++ > 2 files changed, 41 insertions(+) > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index dcc0166d1997..24d5a58467a3 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -456,6 +456,24 @@ config KPROBE_EVENTS > This option is also required by perf-probe subcommand of perf tools. > If you want to use perf tools, this option is strongly recommended. > > +config KPROBE_EVENTS_ON_NOTRACE > + bool "Do NOT protect notrace function from kprobe events" > + depends on KPROBE_EVENTS > + default n > + help > + This is only for the developers who want to debug ftrace itself > + using kprobe events. > + > + Usually, ftrace related functions are protected from kprobe-events > + to prevent an infinit recursion or any unexpected execution path > + which leads to a kernel crash. > + > + This option disables such protection and allows you to put kprobe > + events on ftrace functions for debugging ftrace by itself. > + Note that this might let you shoot yourself in the foot. > + > + If unsure, say N. > + > config UPROBE_EVENTS > bool "Enable uprobes-based dynamic events" > depends on ARCH_SUPPORTS_UPROBES > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index 27ace4513c43..1f1b4d712a7e 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -496,6 +496,23 @@ disable_trace_kprobe(struct trace_kprobe *tk, struct > trace_event_file *file) > return ret; > } > > +#ifdef CONFIG_KPROBE_EVENTS_ON_NOTRACE > +#define within_notrace_func(tk) (false) > +#else > +static bool within_notrace_func(struct trace_kprobe *tk) > +{ > + unsigned long offset, size, addr; > + > + addr = kallsyms_lookup_name(trace_kprobe_symbol(tk)); Oops, I found this is wrong. (Thanks for old myself :P) As ftracetest probepoint.tc said, kprobe-events can be defined without symbol (direct address) for debugging. In that case trace_kprobe_symbol will not return the symbol string. I'll fix this series again. Thank you, > + addr += trace_kprobe_offset(tk); > + > + if (!kallsyms_lookup_size_offset(addr, &size, &offset)) > + return true; /* Out of range. */ > + > + return !ftrace_location_range(addr - offset, addr - offset + size); > +} > +#endif > + > /* Internal register function - just handle k*probes and flags */ > static int __register_trace_kprobe(struct trace_kprobe *tk) > { > @@ -504,6 +521,12 @@ static int __register_trace_kprobe(struct trace_kprobe > *tk) > if (trace_probe_is_registered(&tk->tp)) > return -EINVAL; > > + if (within_notrace_func(tk)) { > + pr_warn("Could not probe notrace function %s\n", > + trace_kprobe_symbol(tk)); > + return -EINVAL; > + } > + > for (i = 0; i < tk->tp.nr_args; i++) > traceprobe_update_arg(&tk->tp.args[i]); > > -- Masami Hiramatsu <mhira...@kernel.org>