Re: [PATCH bpf-next v1 04/19] bpf: allow loading of a bpf_iter program

Martin KaFai Lau
2020-04-29T00:54:34Z

On Mon, Apr 27, 2020 at 01:12:39PM -0700, Yonghong Song wrote:
> A bpf_iter program is a tracing program with attach type
> BPF_TRACE_ITER. The load attribute
> attach_btf_id
> is used by the verifier against a particular kernel function,
> e.g., __bpf_iter__bpf_map in our previous bpf_map iterator.
>
> The program return value must be 0 for now. In the
> future, other return values may be used for filtering or
> teminating the iterator.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/verifier.c | 20 ++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 1 +
> 3 files changed, 22 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4a6c47f3febe..f39b9fec37ab 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -215,6 +215,7 @@ enum bpf_attach_type {
> BPF_TRACE_FEXIT,
> BPF_MODIFY_RETURN,
> BPF_LSM_MAC,
> + BPF_TRACE_ITER,
> __MAX_BPF_ATTACH_TYPE
> };
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 91728e0f27eb..fd36c22685d9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7074,6 +7074,11 @@ static int check_return_code(struct bpf_verifier_env *env)
> return 0;
> range = tnum_const(0);
> break;
> + case BPF_PROG_TYPE_TRACING:
> + if (env->prog->expected_attach_type != BPF_TRACE_ITER)
> + return 0;
> + range = tnum_const(0);
> + break;
> default:
> return 0;
> }
> @@ -10454,6 +10459,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> struct bpf_prog *tgt_prog = prog->aux->linked_prog;
> u32 btf_id = prog->aux->attach_btf_id;
> const char prefix[] = "btf_trace_";
> + struct btf_func_model fmodel;
> int ret = 0, subprog = -1, i;
> struct bpf_trampoline *tr;
> const struct btf_type *t;
> @@ -10595,6 +10601,20 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> prog->aux->attach_func_proto = t;
> prog->aux->attach_btf_trace = true;
> return 0;
> + case BPF_TRACE_ITER:
> + if (!btf_type_is_func(t)) {
> + verbose(env, "attach_btf_id %u is not a function\n",
> + btf_id);
> + return -EINVAL;
> + }
> + t = btf_type_by_id(btf, t->type);
> + if (!btf_type_is_func_proto(t))
Other than the type tests,
to ensure the attach_btf_id is a supported bpf_iter target,
should the prog be checked against the target list
("struct list_head targets") here also during the prog load time?

> + return -EINVAL;
> + prog->aux->attach_func_name = tname;
> + prog->aux->attach_func_proto = t;
> + ret = btf_distill_func_proto(&env->log, btf, t,
> + tname, &fmodel);
> + return ret;
> default:
> if (!prog_extension)
> return -EINVAL;