linux-kernel - [PATCH v3 1/3] tracing: kprobes: Prohibit probing on notrace function

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Date:   Sat, 28 Jul 2018 11:21:35 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     rostedt@...dmis.org,
        Francis Deslauriers <francis.deslauriers@...icios.com>,
        peterz@...radead.org, Shuah Khan <shuah@...nel.org>
Cc:     mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/3] tracing: kprobes: Prohibit probing on notrace function

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@...nel.org>
Tested-by: Francis Deslauriers <francis.deslauriers@...icios.com>
---
  Changes in v2
   - Add CONFIG_KPROBE_EVENTS_ON_NOTRACE kconfig for knocking down
     the protection.
  Changes in v3
   - Fix to check raw-address (no symbol) probe point correctly.
---
 kernel/trace/Kconfig        |   18 +++++++++++++++++
 kernel/trace/trace_kprobe.c |   46 +++++++++++++++++++++++++++++++++++--------
 2 files changed, 55 insertions(+), 9 deletions(-)

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..2bf75af92f16 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -87,6 +87,21 @@ static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
 	return nhit;
 }
 
+static nokprobe_inline
+unsigned long trace_kprobe_address(struct trace_kprobe *tk)
+{
+	unsigned long addr;
+
+	if (tk->symbol) {
+		addr = (unsigned long)
+			kallsyms_lookup_name(trace_kprobe_symbol(tk));
+		addr += tk->rp.kp.offset;
+	} else {
+		addr = (unsigned long)tk->rp.kp.addr;
+	}
+	return addr;
+}
+
 bool trace_kprobe_on_func_entry(struct trace_event_call *call)
 {
 	struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
@@ -99,16 +114,8 @@ bool trace_kprobe_on_func_entry(struct trace_event_call *call)
 bool trace_kprobe_error_injectable(struct trace_event_call *call)
 {
 	struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
-	unsigned long addr;
 
-	if (tk->symbol) {
-		addr = (unsigned long)
-			kallsyms_lookup_name(trace_kprobe_symbol(tk));
-		addr += tk->rp.kp.offset;
-	} else {
-		addr = (unsigned long)tk->rp.kp.addr;
-	}
-	return within_error_injection_list(addr);
+	return within_error_injection_list(trace_kprobe_address(tk));
 }
 
 static int register_kprobe_event(struct trace_kprobe *tk);
@@ -496,6 +503,21 @@ 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 = trace_kprobe_address(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 +526,12 @@ 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]);