tracing/kprobe: Fix to support kretprobe events on unloaded modules

Fix kprobe_on_func_entry() returns error code instead of false so that
register_kretprobe() can return an appropriate error code.

append_trace_kprobe() expects the kprobe registration returns -ENOENT
when the target symbol is not found, and it checks whether the target
module is unloaded or not. If the target module doesn't exist, it
defers to probe the target symbol until the module is loaded.

However, since register_kretprobe() returns -EINVAL instead of -ENOENT
in that case, it always fail on putting the kretprobe event on unloaded
modules. e.g.

Kprobe event:
/sys/kernel/debug/tracing # echo p xfs:xfs_end_io >> kprobe_events
[   16.515574] trace_kprobe: This probe might be able to register after target module is loaded. Continue.

Kretprobe event: (p -> r)
/sys/kernel/debug/tracing # echo r xfs:xfs_end_io >> kprobe_events
sh: write error: Invalid argument
/sys/kernel/debug/tracing # cat error_log
[   41.122514] trace_kprobe: error: Failed to register probe event
  Command: r xfs:xfs_end_io
             ^

To fix this bug, change kprobe_on_func_entry() to detect symbol lookup
failure and return -ENOENT in that case. Otherwise it returns -EINVAL
or 0 (succeeded, given address is on the entry).

Link: https://lkml.kernel.org/r/161176187132.1067016.8118042342894378981.stgit@devnote2

Cc: stable@vger.kernel.org
Fixes: 59158ec4aef7 ("tracing/kprobes: Check the probe on unloaded module correctly")
Reported-by: Jianlin Lv <Jianlin.Lv@arm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index e6fba1798771..56c7fbff7bd7 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -221,9 +221,9 @@ bool trace_kprobe_on_func_entry(struct trace_event_call *call)
 {
 	struct trace_kprobe *tk = trace_kprobe_primary_from_call(call);
 
-	return tk ? kprobe_on_func_entry(tk->rp.kp.addr,
+	return tk ? (kprobe_on_func_entry(tk->rp.kp.addr,
 			tk->rp.kp.addr ? NULL : tk->rp.kp.symbol_name,
-			tk->rp.kp.addr ? 0 : tk->rp.kp.offset) : false;
+			tk->rp.kp.addr ? 0 : tk->rp.kp.offset) == 0) : false;
 }
 
 bool trace_kprobe_error_injectable(struct trace_event_call *call)
@@ -828,9 +828,11 @@ static int trace_kprobe_create(int argc, const char *argv[])
 		}
 		if (is_return)
 			flags |= TPARG_FL_RETURN;
-		if (kprobe_on_func_entry(NULL, symbol, offset))
+		ret = kprobe_on_func_entry(NULL, symbol, offset);
+		if (ret == 0)
 			flags |= TPARG_FL_FENTRY;
-		if (offset && is_return && !(flags & TPARG_FL_FENTRY)) {
+		/* Defer the ENOENT case until register kprobe */
+		if (ret == -EINVAL && is_return) {
 			trace_probe_log_err(0, BAD_RETPROBE);
 			goto parse_error;
 		}