On Thu, Apr 28, 2022 at 9:54 AM Delyan Kratunov <delyank@xxxxxx> 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@xxxxxx>
> ---
> 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
