Re: [PATCH v5 bpf-next 09/11] bpf: Support ->fill_link_info for perf_event

[Yafang Shao <laoar.shao@gmail.com>]

On Sat, Jun 24, 2023 at 5:55 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Jun 23, 2023 at 7:16 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > By introducing support for ->fill_link_info to the perf_event link, users
> > gain the ability to inspect it using `bpftool link show`. While the current
> > approach involves accessing this information via `bpftool perf show`,
> > consolidating link information for all link types in one place offers
> > greater convenience. Additionally, this patch extends support to the
> > generic perf event, which is not currently accommodated by
> > `bpftool perf show`. While only the perf type and config are exposed to
> > userspace, other attributes such as sample_period and sample_freq are
> > ignored. It's important to note that if kptr_restrict is not permitted, the
> > probed address will not be exposed, maintaining security measures.
> >
> > A new enum bpf_perf_event_type is introduced to help the user understand
> > which struct is relevant.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  include/uapi/linux/bpf.h       |  35 +++++++++++++
> >  kernel/bpf/syscall.c           | 115 +++++++++++++++++++++++++++++++++++++++++
> >  tools/include/uapi/linux/bpf.h |  35 +++++++++++++
> >  3 files changed, 185 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 23691ea..1c579d5 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1056,6 +1056,14 @@ enum bpf_link_type {
> >         MAX_BPF_LINK_TYPE,
> >  };
> >
> > +enum bpf_perf_event_type {
> > +       BPF_PERF_EVENT_UNSPEC = 0,
> > +       BPF_PERF_EVENT_UPROBE = 1,
> > +       BPF_PERF_EVENT_KPROBE = 2,
> > +       BPF_PERF_EVENT_TRACEPOINT = 3,
> > +       BPF_PERF_EVENT_EVENT = 4,
> > +};
> > +
> >  /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
> >   *
> >   * NONE(default): No further bpf programs allowed in the subtree.
> > @@ -6443,6 +6451,33 @@ struct bpf_link_info {
> >                         __u32 count;
> >                         __u32 flags;
> >                 } kprobe_multi;
> > +               struct {
> > +                       __u32 type; /* enum bpf_perf_event_type */
> > +                       __u32 :32;
> > +                       union {
> > +                               struct {
> > +                                       __aligned_u64 file_name; /* in/out */
> > +                                       __u32 name_len;
> > +                                       __u32 offset;/* offset from file_name */
> > +                                       __u32 flags;
> > +                               } uprobe; /* BPF_PERF_EVENT_UPROBE */
> > +                               struct {
> > +                                       __aligned_u64 func_name; /* in/out */
> > +                                       __u32 name_len;
> > +                                       __u32 offset;/* offset from func_name */
> > +                                       __u64 addr;
> > +                                       __u32 flags;
> > +                               } kprobe; /* BPF_PERF_EVENT_KPROBE */
> > +                               struct {
> > +                                       __aligned_u64 tp_name;   /* in/out */
> > +                                       __u32 name_len;
> > +                               } tracepoint; /* BPF_PERF_EVENT_TRACEPOINT */
> > +                               struct {
> > +                                       __u64 config;
> > +                                       __u32 type;
> > +                               } event; /* BPF_PERF_EVENT_EVENT */
> > +                       };
> > +               } perf_event;
> >         };
> >  } __attribute__((aligned(8)));
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index c863d39..02dad3c 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3394,9 +3394,124 @@ static int bpf_perf_link_fill_common(const struct perf_event *event,
> >         return 0;
> >  }
> >
> > +#ifdef CONFIG_KPROBE_EVENTS
> > +static int bpf_perf_link_fill_kprobe(const struct perf_event *event,
> > +                                    struct bpf_link_info *info)
> > +{
> > +       char __user *uname;
> > +       u64 addr, offset;
> > +       u32 ulen, type;
> > +       int err;
> > +
> > +       uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
> > +       ulen = info->perf_event.kprobe.name_len;
> > +       info->perf_event.type = BPF_PERF_EVENT_KPROBE;
> > +       err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
> > +                                       &type);
> > +       if (err)
> > +               return err;
> > +
> > +       info->perf_event.kprobe.offset = offset;
> > +       if (type == BPF_FD_TYPE_KRETPROBE)
> > +               info->perf_event.kprobe.flags = 1;
>
> hm... ok, sorry, I didn't realize that these flags are not part of
> UAPI. I don't think just randomly defining 1 to mean retprobe is a
> good approach. Let's drop flags if there are actually no flags.
>
> How about in addition to BPF_PERF_EVENT_UPROBE add
> BPF_PERF_EVENT_URETPROBE, and for BPF_PERF_EVENT_KPROBE add also
> BPF_PERF_EVENT_KRETPROBE. They will share respective perf_event.uprobe
> and perf_event.kprobe sections in bpf_link_info.
>
> It seems consistent with what we did for bpf_task_fd_type enum.

Good idea. Will do it.


-- 
Regards
Yafang