On Wed, Mar 15, 2023 at 3:36 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Add load and run time test for bpf_kfunc_exists() and check that the verifier
> performs dead code elimination for non-existing kfunc.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
we have prog_tests/ksyms_btf.c and progs/test_ksyms_weak.c which do
these kind of tests for variable ksyms, let's just add kfunc ksyms
there (user-space part has also checking that captured pointer value
is correct and stuff like that, we probably want that for kfuncs as
well)
> .../selftests/bpf/progs/task_kfunc_success.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_success.c b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
> index 4f61596b0242..c0a7774e0c79 100644
> --- a/tools/testing/selftests/bpf/progs/task_kfunc_success.c
> +++ b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
> @@ -17,6 +17,8 @@ int err, pid;
> * TP_PROTO(struct task_struct *p, u64 clone_flags)
> */
>
> +void invalid_kfunc(void) __ksym __weak;
> +
> static bool is_test_kfunc_task(void)
> {
> int cur_pid = bpf_get_current_pid_tgid() >> 32;
> @@ -26,7 +28,17 @@ static bool is_test_kfunc_task(void)
>
> static int test_acquire_release(struct task_struct *task)
> {
> - struct task_struct *acquired;
> + struct task_struct *acquired = NULL;
> +
> + if (!bpf_kfunc_exists(bpf_task_acquire)) {
> + err = 3;
> + return 0;
> + }
> + if (bpf_kfunc_exists(invalid_kfunc)) {
> + /* the verifier's dead code elimination should remove this */
> + err = 4;
> + asm volatile ("goto -1"); /* for (;;); */
> + }
>
> acquired = bpf_task_acquire(task);
> bpf_task_release(acquired);
> --
> 2.34.1
>
