Re: [PATCH bpf-next 1/2] bpf, test_run: Add PROG_TEST_RUN support to kprobe

[Song Liu <song@kernel.org>]

On Sun, May 29, 2022 at 3:06 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
>
> This commit adds PROG_TEST_RUN support to BPF_PROG_TYPE_KPROBE progs. On
> top of being generally useful for unit testing kprobe progs, this commit
> more specifically helps solve a relability problem with bpftrace BEGIN
> and END probes.
>
> BEGIN and END probes are run exactly once at the beginning and end of a
> bpftrace tracing session, respectively. bpftrace currently implements
> the probes by creating two dummy functions and attaching the BEGIN and
> END progs, if defined, to those functions and calling the dummy
> functions as appropriate. This works pretty well most of the time except
> for when distros strip symbols from bpftrace. Every now and then this
> happens and users get confused. Having PROG_TEST_RUN support will help
> solve this issue by allowing us to directly trigger uprobes from
> userspace.
>
> Admittedly, this is a pretty specific problem and could probably be
> solved other ways. However, PROG_TEST_RUN also makes unit testing more
> convenient, especially as users start building more complex tracing
> applications. So I see this as killing two birds with one stone.
>
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> ---
>  include/linux/bpf.h      | 10 ++++++++++
>  kernel/trace/bpf_trace.c |  1 +
>  net/bpf/test_run.c       | 36 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 47 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2b914a56a2c5..dec3082ee158 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1751,6 +1751,9 @@ int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
>  int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
>                                 const union bpf_attr *kattr,
>                                 union bpf_attr __user *uattr);
> +int bpf_prog_test_run_kprobe(struct bpf_prog *prog,
> +                            const union bpf_attr *kattr,
> +                            union bpf_attr __user *uattr);
>  bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>                     const struct bpf_prog *prog,
>                     struct bpf_insn_access_aux *info);
> @@ -1998,6 +2001,13 @@ static inline int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog,
>         return -ENOTSUPP;
>  }
>
> +static inline int bpf_prog_test_run_kprobe(struct bpf_prog *prog,
> +                                          const union bpf_attr *kattr,
> +                                          union bpf_attr __user *uattr)
> +{
> +       return -ENOTSUPP;
> +}

As the kernel test bot reported, this is not enough to cover all
different configs. We can
follow the pattern with bpf_prog_test_run_tracing().

Otherwise, this looks good to me.

Song

> +
>  static inline void bpf_map_put(struct bpf_map *map)
>  {
>  }
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10b157a6d73e..b452e84b9ba4 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1363,6 +1363,7 @@ const struct bpf_verifier_ops kprobe_verifier_ops = {
>  };
>
>  const struct bpf_prog_ops kprobe_prog_ops = {
> +       .test_run = bpf_prog_test_run_kprobe,
>  };
>
>  BPF_CALL_5(bpf_perf_event_output_tp, void *, tp_buff, struct bpf_map *, map,
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 56f059b3c242..0b6fc17ce901 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -1622,6 +1622,42 @@ int bpf_prog_test_run_syscall(struct bpf_prog *prog,
>         return err;
>  }
>
> +int bpf_prog_test_run_kprobe(struct bpf_prog *prog,
> +                            const union bpf_attr *kattr,
> +                            union bpf_attr __user *uattr)
> +{
> +       void __user *ctx_in = u64_to_user_ptr(kattr->test.ctx_in);
> +       __u32 ctx_size_in = kattr->test.ctx_size_in;
> +       u32 repeat = kattr->test.repeat;
> +       struct pt_regs *ctx = NULL;
> +       u32 retval, duration;
> +       int err = 0;
> +
> +       if (kattr->test.data_in || kattr->test.data_out ||
> +           kattr->test.ctx_out || kattr->test.flags ||
> +           kattr->test.cpu || kattr->test.batch_size)
> +               return -EINVAL;
> +
> +       if (ctx_size_in != sizeof(struct pt_regs))
> +               return -EINVAL;
> +
> +       ctx = memdup_user(ctx_in, ctx_size_in);
> +       if (IS_ERR(ctx))
> +               return PTR_ERR(ctx);
> +
> +       err = bpf_test_run(prog, ctx, repeat, &retval, &duration, false);
> +       if (err)
> +               goto out;
> +
> +       if (copy_to_user(&uattr->test.retval, &retval, sizeof(retval)) ||
> +           copy_to_user(&uattr->test.duration, &duration, sizeof(duration))) {
> +               err = -EFAULT;
> +       }
> +out:
> +       kfree(ctx);
> +       return err;
> +}
> +
>  static const struct btf_kfunc_id_set bpf_prog_test_kfunc_set = {
>         .owner        = THIS_MODULE,
>         .check_set        = &test_sk_check_kfunc_ids,
> --
> 2.36.1
>