Re: [PATCH v2 bpf-next 2/4] selftests/bpf: add non-BPF_LSM test for task local storage

[Andrii Nakryiko]

On Tue, Jan 26, 2021 at 1:21 AM Song Liu <songliubraving@xxxxxx> wrote:
>
> Task local storage is enabled for tracing programs. Add two tests for
> task local storage without CONFIG_BPF_LSM.
>
> The first test measures the duration of a syscall by storing sys_enter
> time in task local storage.
>
> The second test checks whether the kernel allows allocating task local
> storage in exit_creds() (which it should not).
>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
>  .../bpf/prog_tests/task_local_storage.c       | 85 +++++++++++++++++++
>  .../selftests/bpf/progs/task_local_storage.c  | 56 ++++++++++++
>  .../bpf/progs/task_local_storage_exit_creds.c | 32 +++++++
>  3 files changed, 173 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/task_local_storage.c
>  create mode 100644 tools/testing/selftests/bpf/progs/task_local_storage.c
>  create mode 100644 tools/testing/selftests/bpf/progs/task_local_storage_exit_creds.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
> new file mode 100644
> index 0000000000000..a8e2d3a476145
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Facebook */
> +
> +#include <sys/types.h>
> +#include <unistd.h>
> +#include <test_progs.h>
> +#include "task_local_storage.skel.h"
> +#include "task_local_storage_exit_creds.skel.h"
> +
> +static unsigned int duration;
> +
> +static void check_usleep_duration(struct task_local_storage *skel,
> +                                 __u64 time_us)
> +{
> +       __u64 syscall_duration;
> +
> +       usleep(time_us);
> +
> +       /* save syscall_duration measure in usleep() */
> +       syscall_duration = skel->bss->syscall_duration;
> +
> +       /* time measured by the BPF program (in nanoseconds) should be
> +        * within +/- 20% of time_us * 1000.
> +        */
> +       CHECK(syscall_duration < 800 * time_us, "syscall_duration",
> +             "syscall_duration was too small\n");
> +       CHECK(syscall_duration > 1200 * time_us, "syscall_duration",
> +             "syscall_duration was too big\n");

this is going to be very flaky, especially in Travis CI. Can you
please use something more stable that doesn't rely on time?

> +}
> +
> +static void test_syscall_duration(void)
> +{
> +       struct task_local_storage *skel;
> +       int err;
> +
> +       skel = task_local_storage__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
> +               return;
> +
> +       skel->bss->target_pid = getpid();

you are getting process ID, but comparing it with thread ID in BPF
code. It will stop working properly if/when tests will be run in
separate threads, so please use gettid() instead.

> +
> +       err = task_local_storage__attach(skel);
> +       if (!ASSERT_OK(err, "skel_attach"))
> +               goto out;
> +
> +       check_usleep_duration(skel, 2000);
> +       check_usleep_duration(skel, 3000);
> +       check_usleep_duration(skel, 4000);
> +
> +out:
> +       task_local_storage__destroy(skel);
> +}
> +
> +static void test_exit_creds(void)
> +{
> +       struct task_local_storage_exit_creds *skel;
> +       int err;
> +
> +       skel = task_local_storage_exit_creds__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
> +               return;
> +
> +       err = task_local_storage_exit_creds__attach(skel);
> +       if (!ASSERT_OK(err, "skel_attach"))
> +               goto out;
> +
> +       /* trigger at least one exit_creds() */
> +       if (CHECK_FAIL(system("ls > /dev/null")))
> +               goto out;
> +
> +       /* sync rcu, so the following reads could get latest values */
> +       kern_sync_rcu();

what are we waiting for here? you don't detach anything... system() is
definitely going to complete by now, so whatever counter was or was
not updated will be reflected here. Seems like kern_sync_rcu() is not
needed?

> +       ASSERT_EQ(skel->bss->valid_ptr_count, 0, "valid_ptr_count");
> +       ASSERT_NEQ(skel->bss->null_ptr_count, 0, "null_ptr_count");
> +out:
> +       task_local_storage_exit_creds__destroy(skel);
> +}
> +
> +void test_task_local_storage(void)
> +{
> +       if (test__start_subtest("syscall_duration"))
> +               test_syscall_duration();
> +       if (test__start_subtest("exit_creds"))
> +               test_exit_creds();
> +}

[...]

> +int valid_ptr_count = 0;
> +int null_ptr_count = 0;
> +
> +SEC("fentry/exit_creds")
> +int BPF_PROG(trace_exit_creds, struct task_struct *task)
> +{
> +       __u64 *ptr;
> +
> +       ptr = bpf_task_storage_get(&task_storage, task, 0,
> +                                  BPF_LOCAL_STORAGE_GET_F_CREATE);
> +       if (ptr)
> +               valid_ptr_count++;
> +       else
> +               null_ptr_count++;


use atomic increments?

> +       return 0;
> +}
> --
> 2.24.1
>