netdev - Re: [PATCHv2 bpf-next 5/5] selftests/bpf: Test that module can't be unloaded with attached trampoline

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Date:   Wed, 7 Apr 2021 16:04:48 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...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>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCHv2 bpf-next 5/5] selftests/bpf: Test that module can't be
 unloaded with attached trampoline

On Wed, Apr 7, 2021 at 4:22 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Adding test to verify that once we attach module's trampoline,
> the module can't be unloaded.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

To be fair, to test that you are actually testing what you think you
are testing, you'd have to prove that you *can* detach when no program
is attached to bpf_testmod ;) You'd also need kern_sync_rcu() to wait
for all the async clean up to complete inside the kernel. But that
doesn't interact with other tests well, so I think it's fine.

grumpily due to CHECK() usage (please do consider updating to ASSERT):

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  .../selftests/bpf/prog_tests/module_attach.c  | 23 +++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> index 5bc53d53d86e..d180b8c28287 100644
> --- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
> +++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> @@ -45,12 +45,18 @@ static int trigger_module_test_write(int write_sz)
>         return 0;
>  }
>
> +static int delete_module(const char *name, int flags)
> +{
> +       return syscall(__NR_delete_module, name, flags);
> +}
> +
>  void test_module_attach(void)
>  {
>         const int READ_SZ = 456;
>         const int WRITE_SZ = 457;
>         struct test_module_attach* skel;
>         struct test_module_attach__bss *bss;
> +       struct bpf_link *link;
>         int err;
>
>         skel = test_module_attach__open();
> @@ -84,6 +90,23 @@ void test_module_attach(void)
>         ASSERT_EQ(bss->fexit_ret, -EIO, "fexit_tet");
>         ASSERT_EQ(bss->fmod_ret_read_sz, READ_SZ, "fmod_ret");
>
> +       test_module_attach__detach(skel);
> +
> +       /* attach fentry/fexit and make sure it get's module reference */
> +       link = bpf_program__attach(skel->progs.handle_fentry);
> +       if (CHECK(IS_ERR(link), "attach_fentry", "err: %ld\n", PTR_ERR(link)))
> +               goto cleanup;
> +
> +       ASSERT_ERR(delete_module("bpf_testmod", 0), "delete_module");
> +       bpf_link__destroy(link);
> +
> +       link = bpf_program__attach(skel->progs.handle_fexit);
> +       if (CHECK(IS_ERR(link), "attach_fexit", "err: %ld\n", PTR_ERR(link)))
> +               goto cleanup;
> +
> +       ASSERT_ERR(delete_module("bpf_testmod", 0), "delete_module");
> +       bpf_link__destroy(link);
> +
>  cleanup:
>         test_module_attach__destroy(skel);
>  }
> --
> 2.30.2
>