[bpf-next,v9,03/23] selftests/bpf: add test for accessing ctx from syscall program type

We need to also export the kfunc set to the syscall program type,
and then add a couple of eBPF programs that are testing those calls.

The first one checks for valid access, and the second one is OK
from a static analysis point of view but fails at run time because
we are trying to access outside of the allocated memory.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

no changes in v9

no changes in v8

changes in v7:
- add 1 more case to ensure we can read the entire sizeof(ctx)
- add a test case for when the context is NULL

new in v6
---
 net/bpf/test_run.c                            |  1 +
 .../selftests/bpf/prog_tests/kfunc_call.c     | 28 +++++++++++++++
 .../selftests/bpf/progs/kfunc_call_test.c     | 36 +++++++++++++++++++
 3 files changed, 65 insertions(+)

On Wed, 24 Aug 2022 at 15:41, Benjamin Tissoires
<benjamin.tissoires@redhat.com> wrote:
>
> We need to also export the kfunc set to the syscall program type,
> and then add a couple of eBPF programs that are testing those calls.
>
> The first one checks for valid access, and the second one is OK
> from a static analysis point of view but fails at run time because
> we are trying to access outside of the allocated memory.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
>
> ---
>
> no changes in v9
>
> no changes in v8
>
> changes in v7:
> - add 1 more case to ensure we can read the entire sizeof(ctx)
> - add a test case for when the context is NULL
>
> new in v6
> ---
>  net/bpf/test_run.c                            |  1 +
>  .../selftests/bpf/prog_tests/kfunc_call.c     | 28 +++++++++++++++
>  .../selftests/bpf/progs/kfunc_call_test.c     | 36 +++++++++++++++++++
>  3 files changed, 65 insertions(+)
>
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 25d8ecf105aa..f16baf977a21 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -1634,6 +1634,7 @@ static int __init bpf_prog_test_run_init(void)
>
>         ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_prog_test_kfunc_set);
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_prog_test_kfunc_set);
> +       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_prog_test_kfunc_set);
>         return ret ?: register_btf_id_dtor_kfuncs(bpf_prog_test_dtor_kfunc,
>                                                   ARRAY_SIZE(bpf_prog_test_dtor_kfunc),
>                                                   THIS_MODULE);
> diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> index eede7c304f86..1edad012fe01 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> +++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> @@ -9,10 +9,22 @@
>
>  #include "cap_helpers.h"
>
> +struct syscall_test_args {
> +       __u8 data[16];
> +       size_t size;
> +};
> +
>  static void test_main(void)
>  {
>         struct kfunc_call_test_lskel *skel;
>         int prog_fd, err;
> +       struct syscall_test_args args = {
> +               .size = 10,
> +       };
> +       DECLARE_LIBBPF_OPTS(bpf_test_run_opts, syscall_topts,
> +               .ctx_in = &args,
> +               .ctx_size_in = sizeof(args),
> +       );
>         LIBBPF_OPTS(bpf_test_run_opts, topts,
>                 .data_in = &pkt_v4,
>                 .data_size_in = sizeof(pkt_v4),
> @@ -38,6 +50,22 @@ static void test_main(void)
>         ASSERT_OK(err, "bpf_prog_test_run(test_ref_btf_id)");
>         ASSERT_EQ(topts.retval, 0, "test_ref_btf_id-retval");
>
> +       prog_fd = skel->progs.kfunc_syscall_test.prog_fd;
> +       err = bpf_prog_test_run_opts(prog_fd, &syscall_topts);
> +       ASSERT_OK(err, "bpf_prog_test_run(syscall_test)");
> +
> +       prog_fd = skel->progs.kfunc_syscall_test_fail.prog_fd;
> +       err = bpf_prog_test_run_opts(prog_fd, &syscall_topts);
> +       ASSERT_ERR(err, "bpf_prog_test_run(syscall_test_fail)");

It would be better to assert on the verifier error string, to make
sure we continue actually testing the error we care about and not
something else.

> +
> +       syscall_topts.ctx_in = NULL;
> +       syscall_topts.ctx_size_in = 0;
> +
> +       prog_fd = skel->progs.kfunc_syscall_test_null.prog_fd;
> +       err = bpf_prog_test_run_opts(prog_fd, &syscall_topts);
> +       ASSERT_OK(err, "bpf_prog_test_run(syscall_test_null)");
> +       ASSERT_EQ(syscall_topts.retval, 0, "syscall_test_null-retval");
> +
>         kfunc_call_test_lskel__destroy(skel);
>  }
>
> diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> index 5aecbb9fdc68..da7ae0ef9100 100644
> --- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> +++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> @@ -92,4 +92,40 @@ int kfunc_call_test_pass(struct __sk_buff *skb)
>         return 0;
>  }
>
> +struct syscall_test_args {
> +       __u8 data[16];
> +       size_t size;
> +};
> +
> +SEC("syscall")
> +int kfunc_syscall_test(struct syscall_test_args *args)
> +{
> +       const int size = args->size;
> +
> +       if (size > sizeof(args->data))
> +               return -7; /* -E2BIG */
> +
> +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(args->data));
> +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args));
> +       bpf_kfunc_call_test_mem_len_pass1(&args->data, size);
> +
> +       return 0;
> +}
> +
> +SEC("syscall")
> +int kfunc_syscall_test_null(struct syscall_test_args *args)
> +{
> +       bpf_kfunc_call_test_mem_len_pass1(args, 0);
> +

Where is it testing 'NULL'? It is testing zero_size_allowed.

> +       return 0;
> +}
> +
> +SEC("syscall")
> +int kfunc_syscall_test_fail(struct syscall_test_args *args)
> +{
> +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args) + 1);
> +
> +       return 0;
> +}
> +
>  char _license[] SEC("license") = "GPL";
> --
> 2.36.1
>