[PATCH v2 bpf 1/3] ftrace: Fix BPF fexit with livepatch

[PATCH v2 bpf 1/3] ftrace: Fix BPF fexit with livepatch

[Song Liu]

When livepatch is attached to the same function as bpf trampoline with
a fexit program, bpf trampoline code calls register_ftrace_direct()
twice. The first time will fail with -EAGAIN, and the second time it
will succeed. This requires register_ftrace_direct() to unregister
the address on the first attempt. Otherwise, the bpf trampoline cannot
attach. Here is an easy way to reproduce this issue:

  insmod samples/livepatch/livepatch-sample.ko
  bpftrace -e 'fexit:cmdline_proc_show {}'
  ERROR: Unable to attach probe: fexit:vmlinux:cmdline_proc_show...

Fix this by cleaning up the hash when register_ftrace_function_nolock hits
errors.

Fixes: d05cb470663a ("ftrace: Fix modification of direct_function hash while in use")
Cc: stable@vger.kernel.org # v6.6+
Reported-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Closes: https://lore.kernel.org/live-patching/c5058315a39d4615b333e485893345be@crowdstrike.com/
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-and-tested-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/trace/ftrace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 42bd2ba68a82..7f432775a6b5 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6048,6 +6048,8 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
 	ops->direct_call = addr;
 
 	err = register_ftrace_function_nolock(ops);
+	if (err)
+		remove_direct_functions_hash(hash, addr);
 
  out_unlock:
 	mutex_unlock(&direct_mutex);
-- 
2.47.3