tracing/kprobes: Fix within_notrace_func() to check only notrace functions

Fix within_notrace_func() to check only notrace functions and to ignore the
kprobe-event which can not solve symbol addresses.

within_notrace_func() returns true if the given kprobe events probe point
seems to be out-of-range. But that is not the correct place to check for it,
it should be done in kprobes afterwards.

kprobe-events allow users to define a probe point on "currently unloaded
module" so that it can trace the event during module load. In this case, the
user will put a probe on a symbol which is not in kallsyms yet and it hits
the within_notrace_func().  As a result, kprobe-events always refuses if
user defines a probe on a "currenly unloaded module".

Fixes: commit 45408c4f ("tracing: kprobes: Prohibit probing on notrace function")
Link: http://lkml.kernel.org/r/153319624799.29007.13604430345640129926.stgit@devboxSigned-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -88,6 +88,7 @@ static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
 	return nhit;
 }
 
+/* Return 0 if it fails to find the symbol address */
 static nokprobe_inline
 unsigned long trace_kprobe_address(struct trace_kprobe *tk)
 {
@@ -96,7 +97,8 @@ unsigned long trace_kprobe_address(struct trace_kprobe *tk)
 	if (tk->symbol) {
 		addr = (unsigned long)
 			kallsyms_lookup_name(trace_kprobe_symbol(tk));
-		addr += tk->rp.kp.offset;
+		if (addr)
+			addr += tk->rp.kp.offset;
 	} else {
 		addr = (unsigned long)tk->rp.kp.addr;
 	}
@@ -519,8 +521,8 @@ 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. */
+	if (!addr || !kallsyms_lookup_size_offset(addr, &size, &offset))
+		return false;
 
 	return !ftrace_location_range(addr - offset, addr - offset + size);
 }