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

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Before the 0bc11ed5ab60 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: Chuang Wang <nashuiliang@gmail.com>
Signed-off-by: Jingren Zhou <zhoujingren@didiglobal.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220629151848.65587-2-nashuiliang@gmail.com
This commit is contained in:
Chuang Wang 2022-06-29 23:18:45 +08:00 committed by Andrii Nakryiko
parent f6b9f6d57e
commit 8094029330
1 changed files with 14 additions and 4 deletions
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18
tools/lib/bpf/libbpf.c
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@ -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);