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

From: Yonghong Song <[email-masked]>
Date: Mon, 27 Apr 2020 13:12:39 -0700

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 <[email-masked]>
---
 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))
+			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;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 4a6c47f3febe..f39b9fec37ab 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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
 };
 
-- 
2.24.1