Re: [PATCH bpf-next v2 2/2] selftests/bpf: Add test to verify the fix of kprobe_write_ctx abuse

[Jiri Olsa]

On Thu, Mar 26, 2026 at 10:17:18PM +0800, Leon Hwang wrote:

SNIP

> +     prog_fd = bpf_program__fd(skel_kprobe->progs.kprobe_write_ctx);
> +     bpf_program__set_attach_target(prog_ext, prog_fd, "kprobe_write_ctx");
> +
> +     err = kprobe_write_ctx__load(skel_ext);
> +     if (!ASSERT_OK(err, "kprobe_write_ctx__load ext"))
> +             goto out;
> +
> +     prog_fd = bpf_program__fd(prog_kprobe);
> +     link_ext = bpf_program__attach_freplace(prog_ext, prog_fd, 
> "kprobe_dummy");
> +     ASSERT_ERR_PTR(link_ext, "bpf_program__attach_freplace link");
> +     ASSERT_EQ(errno, EINVAL, "bpf_program__attach_freplace errno");

nit, I prefer libbpf_get_error call instead, because it's not obvious
that ASSERT_ERR_PTR sets errno, smth like:

        if (!ASSERT_EQ(libbpf_get_error(link_ext), -EINVAL, ..

anyway lgtm

Acked-by: Jiri Olsa <jo...@kernel.org>

thanks,
jirka


> +
> +     link_kprobe = bpf_program__attach_kprobe_opts(prog_kprobe, 
> "bpf_fentry_test1",
> +                                                   &kprobe_opts);
> +     if (!ASSERT_OK_PTR(link_kprobe, "bpf_program__attach_kprobe_opts"))
> +             goto out;
> +
> +     err = bpf_prog_test_run_opts(bpf_program__fd(prog_fentry), &topts);
> +     ASSERT_OK(err, "bpf_prog_test_run_opts");
> +
> +out:
> +     bpf_link__destroy(link_ext);
> +     bpf_link__destroy(link_kprobe);
> +     kprobe_write_ctx__destroy(skel_ext);
> +     kprobe_write_ctx__destroy(skel_kprobe);
> +}
>  #else
>  static void test_attach_kprobe_write_ctx(void)
>  {
>       test__skip();
>  }
> +
> +static void test_freplace_kprobe_write_ctx(void)
> +{
> +     test__skip();
> +}
>  #endif
>  
>  static void test_attach_probe_auto(struct test_attach_probe *skel)
> @@ -434,6 +496,8 @@ void test_attach_probe(void)
>               test_attach_kprobe_long_event_name();
>       if (test__start_subtest("kprobe-write-ctx"))
>               test_attach_kprobe_write_ctx();
> +     if (test__start_subtest("freplace-kprobe-write-ctx"))
> +             test_freplace_kprobe_write_ctx();
>  
>  cleanup:
>       test_attach_probe__destroy(skel);
> diff --git a/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c 
> b/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c
> index f77aef0474d3..adbf52afe490 100644
> --- a/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c
> +++ b/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c
> @@ -19,4 +19,23 @@ int kprobe_multi_write_ctx(struct pt_regs *ctx)
>       ctx->ax = 0;
>       return 0;
>  }
> +
> +SEC("?kprobe")
> +int kprobe_dummy(struct pt_regs *regs)
> +{
> +     return 0;
> +}
> +
> +SEC("?freplace")
> +int freplace_kprobe(struct pt_regs *regs)
> +{
> +     regs->di = 0;
> +     return 0;
> +}
> +
> +SEC("?fentry/bpf_fentry_test1")
> +int BPF_PROG(fentry)
> +{
> +     return 0;
> +}
>  #endif
> -- 
> 2.53.0
>