On Wed, May 13, 2020 at 10:32 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> Currently, tracing/fentry and tracing/fexit prog
> return values are not enforced. In trampoline codes,
> the fentry/fexit prog return values are ignored.
> Let us enforce it to be 0 to avoid confusion and
> allows potential future extension.
>
> This patch also explicitly added return value
> checking for tracing/raw_tp, tracing/fmod_ret,
> and freplace programs such that these program
> return values can be anything. The purpose are
> two folds:
> 1. to make it explicit about return value expectations
> for these programs in verifier.
> 2. for tracing prog_type, if a future attach type
> is added, the default is -ENOTSUPP which will
> enforce to specify return value ranges explicitly.
>
> Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline")
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
Looks good, except a nit below.
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index fa1d8245b925..2d80cce0a28a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7059,6 +7059,24 @@ static int check_return_code(struct bpf_verifier_env *env)
> return 0;
> range = tnum_const(0);
> break;
> + case BPF_PROG_TYPE_TRACING:
> + switch ((env->prog->expected_attach_type)) {
nit: extra pair of ()?
> + case BPF_TRACE_FENTRY:
> + case BPF_TRACE_FEXIT:
> + range = tnum_const(0);
> + break;
> + case BPF_TRACE_RAW_TP:
> + case BPF_MODIFY_RETURN:
> + return 0;
> + default:
> + return -ENOTSUPP;
> + }
> +
> + break;
> + case BPF_PROG_TYPE_EXT:
> + /* freplace program can return anything as its return value
> + * depends on the to-be-replaced kernel func or bpf program.
> + */
> default:
> return 0;
> }
> --
> 2.24.1
>
