[PATCH v2 1/3] tracing: kprobes: Prohibit probing on notrace function

[Masami Hiramatsu]

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 <mhiramat@xxxxxxxxxx>
Tested-by: Francis Deslauriers <francis.deslauriers@xxxxxxxxxxxx>
---
  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));
+	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]);