Re: [PATCH bpf-next 3/5] bpf: allow sleepable uprobe programs to attach

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Apr 28, 2022 at 9:54 AM Delyan Kratunov <delyank@fb.com> wrote:
>
> uprobe and kprobe programs have the same program type, KPROBE, which is
> currently not allowed to load sleepable programs.
>
> To avoid adding a new UPROBE type, we instead allow sleepable KPROBE
> programs to load and defer the is-it-actually-a-uprobe-program check
> to attachment time, where we're already validating the corresponding
> perf_event.
>
> A corollary of this patch is that you can now load a sleepable kprobe
> program but cannot attach it.
>
> Signed-off-by: Delyan Kratunov <delyank@fb.com>
> ---
>  kernel/bpf/syscall.c  | 8 ++++++++
>  kernel/bpf/verifier.c | 4 ++--
>  2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index e9e3e49c0eb7..3ce923f489d7 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3009,6 +3009,14 @@ static int bpf_perf_link_attach(const union bpf_attr *attr, struct bpf_prog *pro
>         }
>
>         event = perf_file->private_data;
> +       if (prog->aux->sleepable) {
> +               if (!event->tp_event || (event->tp_event->flags & TRACE_EVENT_FL_UPROBE) == 0) {

so far TRACE_EVENT_FL_UPROBE was contained to within kernel/trace so
far, maybe it's better to instead expose a helper function to check if
perf_event represents uprobe?

> +                       err = -EINVAL;
> +                       bpf_link_cleanup(&link_primer);
> +                       goto out_put_file;
> +               }
> +       }
> +
>         err = perf_event_set_bpf_prog(event, prog, attr->link_create.perf_event.bpf_cookie);
>         if (err) {
>                 bpf_link_cleanup(&link_primer);
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 71827d14724a..c6258118dd75 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -14313,8 +14313,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>         }
>
>         if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
> -           prog->type != BPF_PROG_TYPE_LSM) {
> -               verbose(env, "Only fentry/fexit/fmod_ret and lsm programs can be sleepable\n");
> +           prog->type != BPF_PROG_TYPE_LSM && prog->type != BPF_PROG_TYPE_KPROBE) {
> +               verbose(env, "Only fentry/fexit/fmod_ret, lsm, and kprobe/uprobe programs can be sleepable\n");
>                 return -EINVAL;
>         }
>
> --
> 2.35.1