linux-kernel - [for-next][PATCH 14/18] tracing/kprobes: Check the probe on unloaded module correctly

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Date:   Sun, 28 Oct 2018 03:30:02 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [for-next][PATCH 14/18] tracing/kprobes: Check the probe on unloaded module correctly

From: Masami Hiramatsu <mhiramat@...nel.org>

Current kprobe event doesn't checks correctly whether the
given event is on unloaded module or not. It just checks
the event has ":" in the name.

That is not enough because if we define a probe on non-exist
symbol on loaded module, it allows to define that (with
warning message)

To ensure it correctly, this searches the module name on
loaded module list and only if there is not, it allows to
define it. (this event will be available when the target
module is loaded)

Link: http://lkml.kernel.org/r/153547309528.26502.8300278470528281328.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_kprobe.c | 39 ++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3faaadbddf54..4727a13824f0 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -62,9 +62,23 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
 	return strncmp(mod->name, name, len) == 0 && name[len] == ':';
 }
 
-static nokprobe_inline bool trace_kprobe_is_on_module(struct trace_kprobe *tk)
+static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 {
-	return !!strchr(trace_kprobe_symbol(tk), ':');
+	char *p;
+	bool ret;
+
+	if (!tk->symbol)
+		return false;
+	p = strchr(tk->symbol, ':');
+	if (!p)
+		return true;
+	*p = '\0';
+	mutex_lock(&module_mutex);
+	ret = !!find_module(tk->symbol);
+	mutex_unlock(&module_mutex);
+	*p = ':';
+
+	return ret;
 }
 
 static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
@@ -374,19 +388,13 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 	else
 		ret = register_kprobe(&tk->rp.kp);
 
-	if (ret == 0)
+	if (ret == 0) {
 		tk->tp.flags |= TP_FLAG_REGISTERED;
-	else {
-		if (ret == -ENOENT && trace_kprobe_is_on_module(tk)) {
-			pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
-			ret = 0;
-		} else if (ret == -EILSEQ) {
-			pr_warn("Probing address(0x%p) is not an instruction boundary.\n",
-				tk->rp.kp.addr);
-			ret = -EINVAL;
-		}
+	} else if (ret == -EILSEQ) {
+		pr_warn("Probing address(0x%p) is not an instruction boundary.\n",
+			tk->rp.kp.addr);
+		ret = -EINVAL;
 	}
-
 	return ret;
 }
 
@@ -449,6 +457,11 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
 
 	/* Register k*probe */
 	ret = __register_trace_kprobe(tk);
+	if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
+		pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
+		ret = 0;
+	}
+
 	if (ret < 0)
 		unregister_kprobe_event(tk);
 	else
-- 
2.19.0