Commit 80940293 authored by Chuang Wang's avatar Chuang Wang Committed by Andrii Nakryiko
Browse files

libbpf: Cleanup the legacy kprobe_event on failed add/attach_event() 



Before the 0bc11ed5 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XXX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY. As follows:

1) add a livepatch

$ insmod livepatch-XXX.ko

2) add a kprobe using tracefs API (i.e. add_kprobe_event_legacy)

$ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events

3) enable this kprobe (i.e. sys_perf_event_open)

This will return an error, -EBUSY.

On Andrii Nakryiko's comment, few error paths in
bpf_program__attach_kprobe_opts() that should need to call
remove_kprobe_event_legacy().

With this patch, whenever an error is returned after
add_kprobe_event_legacy() or bpf_program__attach_perf_event_opts(), this
ensures that the created kprobe_event is cleaned.

Signed-off-by: default avatarChuang Wang <nashuiliang@gmail.com>
Signed-off-by: default avatarJingren Zhou <zhoujingren@didiglobal.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220629151848.65587-2-nashuiliang@gmail.com
parent f6b9f6d5

tools/lib/bpf/libbpf.c

+14 −4
Original line number Diff line number Diff line
@@ -9877,10 +9877,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe, 
	}

	type = determine_kprobe_perf_type_legacy(probe_name, retprobe);

	if (type < 0) {

		err = type;

		pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",

			kfunc_name, offset,

			libbpf_strerror_r(type, errmsg, sizeof(errmsg)));

		return type;

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		goto err_clean_legacy;

	}

	attr.size = sizeof(attr);

	attr.config = type;
@@ -9894,9 +9895,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe, 
		err = -errno;

		pr_warn("legacy kprobe perf_event_open() failed: %s\n",

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		return err;

		goto err_clean_legacy;

	}

	return pfd;



err_clean_legacy:

	/* Clear the newly added legacy kprobe_event */

	remove_kprobe_event_legacy(probe_name, retprobe);

	return err;

}



struct bpf_link *
@@ -9953,7 +9959,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
			prog->name, retprobe ? "kretprobe" : "kprobe",

			func_name, offset,

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		goto err_out;

		goto err_clean_legacy;

	}

	if (legacy) {

		struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
@@ -9964,6 +9970,10 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
	}



	return link;



err_clean_legacy:

	if (legacy)

		remove_kprobe_event_legacy(legacy_probe, retprobe);

err_out:

	free(legacy_probe);

	return libbpf_err_ptr(err);