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>
