linux-kernel - Re: [PATCH 08/13] bpf: Add kprobe link for attaching raw kprobes

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Date:   Wed, 5 Jan 2022 20:30:56 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 08/13] bpf: Add kprobe link for attaching raw kprobes

On Tue, Jan 4, 2022 at 12:10 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> Adding new link type BPF_LINK_TYPE_KPROBE to attach kprobes
> directly through register_kprobe/kretprobe API.
>
> Adding new attach type BPF_TRACE_RAW_KPROBE that enables
> such link for kprobe program.
>
> The new link allows to create multiple kprobes link by using
> new link_create interface:
>
>   struct {
>     __aligned_u64   addrs;
>     __u32           cnt;
>     __u64           bpf_cookie;

I'm afraid bpf_cookie has to be different for each addr, otherwise
it's severely limiting. So it would be an array of cookies alongside
an array of addresses

>   } kprobe;
>
> Plus new flag BPF_F_KPROBE_RETURN for link_create.flags to
> create return probe.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/linux/bpf_types.h      |   1 +
>  include/uapi/linux/bpf.h       |  12 +++
>  kernel/bpf/syscall.c           | 191 ++++++++++++++++++++++++++++++++-
>  tools/include/uapi/linux/bpf.h |  12 +++
>  4 files changed, 211 insertions(+), 5 deletions(-)
>

[...]

> @@ -1111,6 +1113,11 @@ enum bpf_link_type {
>   */
>  #define BPF_F_SLEEPABLE                (1U << 4)
>
> +/* link_create flags used in LINK_CREATE command for BPF_TRACE_RAW_KPROBE
> + * attach type.
> + */
> +#define BPF_F_KPROBE_RETURN    (1U << 0)
> +

we have plenty of flexibility to have per-link type fields, so why not
add `bool is_retprobe` next to addrs and cnt?

>  /* When BPF ldimm64's insn[0].src_reg != 0 then this can have
>   * the following extensions:
>   *
> @@ -1465,6 +1472,11 @@ union bpf_attr {
>                                  */
>                                 __u64           bpf_cookie;
>                         } perf_event;
> +                       struct {
> +                               __aligned_u64   addrs;
> +                               __u32           cnt;
> +                               __u64           bpf_cookie;
> +                       } kprobe;
>                 };
>         } link_create;
>

[...]