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SubjectRe: [PATCH 2/2] kprobe: fix: Add ftrace_ops_assist_func to kprobe blacklist
On Sat, 17 Mar 2018 10:22:11 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Or, we can check it by ftrace_location_range() as below patch.

Cute ;-)

>
> Note that as a side-effect, we can not trace functions in trace_kprobe.c
> anymore, and this means it is hard to me to make a testcase of kprobe events.
> It was the easiest (and maintainable) way to make test cases... sigh.
>
> -----
> tracing: kprobes: Prohibit probing on notrace function
>
> From: Masami Hiramatsu <mhiramat@kernel.org>
>
> 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.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> kernel/trace/trace_kprobe.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5ce9b8cf7be3..7404b012e51a 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -487,6 +487,23 @@ disable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
> return ret;
> }
>
> +#ifdef CONFIG_KPROBES_ON_FTRACE
> +static bool within_notrace_func(struct trace_kprobe *tk)
> +{
> + unsigned long offset, size, addr;
> +
> + addr = kallsyms_lookup_name(trace_kprobe_symbol(tk));
> + 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);
> +}
> +#else
> +#define within_notrace_func(tk) (false)
> +#endif
> +
> /* Internal register function - just handle k*probes and flags */
> static int __register_trace_kprobe(struct trace_kprobe *tk)
> {
> @@ -495,6 +512,12 @@ 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;
> + }

This will prevent probing assembly code. Do we want to do that? Or is
kprobes already prohibited from doing so?

-- Steve


> +
> for (i = 0; i < tk->tp.nr_args; i++)
> traceprobe_update_arg(&tk->tp.args[i]);
>
>

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