Commit 56b3c85e authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

ftrace: Fix BPF fexit with livepatch 



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.

Also, move the code that resets ops->func and ops->trampoline to the error
path of register_ftrace_direct(); and add a helper function reset_direct()
in register_ftrace_direct() and unregister_ftrace_direct().

Fixes: d05cb470 ("ftrace: Fix modification of direct_function hash while in use")
Cc: stable@vger.kernel.org # v6.6+
Reported-by: default avatarAndrey 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: default avatarAndrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Reviewed-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251027175023.1521602-2-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 6146a0f1

kernel/bpf/trampoline.c

+0 −5
Original line number Diff line number Diff line
@@ -479,11 +479,6 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut 
		 * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the

		 * trampoline again, and retry register.

		 */

		/* reset fops->func and fops->trampoline for re-register */

		tr->fops->func = NULL;

		tr->fops->trampoline = 0;



		/* free im memory and reallocate later */

		bpf_tramp_image_free(im);

		goto again;

	}

kernel/trace/ftrace.c

+14 −6
Original line number Diff line number Diff line
@@ -5953,6 +5953,17 @@ static void register_ftrace_direct_cb(struct rcu_head *rhp) 
	free_ftrace_hash(fhp);

}



static void reset_direct(struct ftrace_ops *ops, unsigned long addr)

{

	struct ftrace_hash *hash = ops->func_hash->filter_hash;



	remove_direct_functions_hash(hash, addr);



	/* cleanup for possible another register call */

	ops->func = NULL;

	ops->trampoline = 0;

}



/**

 * register_ftrace_direct - Call a custom trampoline directly

 * for multiple functions registered in @ops
@@ -6048,6 +6059,8 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) 
	ops->direct_call = addr;



	err = register_ftrace_function_nolock(ops);

	if (err)

		reset_direct(ops, addr);



 out_unlock:

	mutex_unlock(&direct_mutex);
@@ -6080,7 +6093,6 @@ EXPORT_SYMBOL_GPL(register_ftrace_direct); 
int unregister_ftrace_direct(struct ftrace_ops *ops, unsigned long addr,

			     bool free_filters)

{

	struct ftrace_hash *hash = ops->func_hash->filter_hash;

	int err;



	if (check_direct_multi(ops))
@@ -6090,13 +6102,9 @@ int unregister_ftrace_direct(struct ftrace_ops *ops, unsigned long addr, 


	mutex_lock(&direct_mutex);

	err = unregister_ftrace_function(ops);

	remove_direct_functions_hash(hash, addr);

	reset_direct(ops, addr);

	mutex_unlock(&direct_mutex);



	/* cleanup for possible another register call */

	ops->func = NULL;

	ops->trampoline = 0;



	if (free_filters)

		ftrace_free_filter(ops);

	return err;