On Sat, Jun 25, 2022 at 8:13 PM Chuang W <nashuiliang@xxxxxxxxx> wrote:
>
> 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() which 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 W <nashuiliang@xxxxxxxxx>
Is this your full name? Signed-off-by is required to have a full name
of a person, please update if it's not
> Signed-off-by: Jingren Zhou <zhoujingren@xxxxxxxxxxxxxx>
> ---
> V2->v3:
> - add detail commits
> - call remove_kprobe_event_legacy() on failed bpf_program__attach_perf_event_opts()
>
> tools/lib/bpf/libbpf.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 49e359cd34df..038b0cb3313f 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10811,10 +10811,11 @@ 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 clear_kprobe_event;
> }
> attr.size = sizeof(attr);
> attr.config = type;
> @@ -10828,9 +10829,14 @@ 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 clear_kprobe_event;
> }
> return pfd;
> +
> +clear_kprobe_event:
> + /* Clear the newly added legacy kprobe_event */
> + remove_kprobe_event_legacy(probe_name, retprobe);
> + return err;
> }
>
this part looks good
> struct bpf_link *
> @@ -10899,6 +10905,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>
> return link;
> err_out:
> + /* Clear the newly added legacy kprobe_event */
> + if (legacy)
> + remove_kprobe_event_legacy(legacy_probe, retprobe);
this one will call remove_kprobe_event_legacy() even if we failed to
create that kprobe_event in the first place. So let's maybe add
err_clean_legacy:
if (legacy)
remove_kprobe_event_legacy(legacy_probe, retprobe);
before err_out: and goto there if we fail to attach (but not if we
fail to create pfd)?
Also, looking through libbpf code, I realized that we have exactly the
same problem for uprobes, so please add same fixed to
perf_event_uprobe_open_legacy and attach_uprobe_opts. Thanks!
> free(legacy_probe);
> return libbpf_err_ptr(err);
> }
> --
> 2.34.1
>
