bpf: Add bpf_mptcp_sched_ops

This patch implements a new struct bpf_struct_ops: bpf_mptcp_sched_ops.
Register and unregister the bpf scheduler in .reg and .unreg.

Add write access for the scheduled flag of struct mptcp_subflow_context
in .btf_struct_access.

This MPTCP BPF scheduler implementation is similar to BPF TCP CC. And
net/ipv4/bpf_tcp_ca.c is a frame of reference for this patch.

Acked-by: Paolo Abeni <[email protected]>
Reviewed-by: Mat Martineau <[email protected]>
Co-developed-by: Matthieu Baerts <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>
Co-developed-by: Gregory Detal <[email protected]>
Signed-off-by: Gregory Detal <[email protected]>
Signed-off-by: Geliang Tang <[email protected]>

Author: Geliang Tang

net/mptcp/bpf.c

@@ -10,8 +10,189 @@
 #define pr_fmt(fmt) "MPTCP: " fmt
 
 #include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+#include <net/bpf_sk_storage.h>
 #include "protocol.h"
 
+#ifdef CONFIG_BPF_JIT
+static struct bpf_struct_ops bpf_mptcp_sched_ops;
+static const struct btf_type *mptcp_sock_type, *mptcp_subflow_type __read_mostly;
+static u32 mptcp_sock_id, mptcp_subflow_id;
+
+static const struct bpf_func_proto *
+bpf_mptcp_sched_get_func_proto(enum bpf_func_id func_id,
+			       const struct bpf_prog *prog)
+{
+	switch (func_id) {
+	case BPF_FUNC_sk_storage_get:
+		return &bpf_sk_storage_get_proto;
+	case BPF_FUNC_sk_storage_delete:
+		return &bpf_sk_storage_delete_proto;
+	case BPF_FUNC_skc_to_tcp6_sock:
+		return &bpf_skc_to_tcp6_sock_proto;
+	case BPF_FUNC_skc_to_tcp_sock:
+		return &bpf_skc_to_tcp_sock_proto;
+	default:
+		return bpf_base_func_proto(func_id, prog);
+	}
+}
+
+static int bpf_mptcp_sched_btf_struct_access(struct bpf_verifier_log *log,
+					     const struct bpf_reg_state *reg,
+					     int off, int size)
+{
+	const struct btf_type *t;
+	size_t end;
+
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+
+	if (t == mptcp_sock_type) {
+		switch (off) {
+		case offsetof(struct mptcp_sock, snd_burst):
+			end = offsetofend(struct mptcp_sock, snd_burst);
+			break;
+		default:
+			bpf_log(log, "no write support to mptcp_sock at off %d\n",
+				off);
+			return -EACCES;
+		}
+	} else if (t == mptcp_subflow_type) {
+		switch (off) {
+		case offsetof(struct mptcp_subflow_context, avg_pacing_rate):
+			end = offsetofend(struct mptcp_subflow_context, avg_pacing_rate);
+			break;
+		default:
+			bpf_log(log, "no write support to mptcp_subflow_context at off %d\n",
+				off);
+			return -EACCES;
+		}
+	} else {
+		bpf_log(log, "only access to mptcp sock or subflow is supported\n");
+		return -EACCES;
+	}
+
+	if (off + size > end) {
+		bpf_log(log, "access beyond %s at off %u size %u ended at %zu",
+			t == mptcp_sock_type ? "mptcp_sock" : "mptcp_subflow_context",
+			off, size, end);
+		return -EACCES;
+	}
+
+	return NOT_INIT;
+}
+
+static const struct bpf_verifier_ops bpf_mptcp_sched_verifier_ops = {
+	.get_func_proto		= bpf_mptcp_sched_get_func_proto,
+	.is_valid_access	= bpf_tracing_btf_ctx_access,
+	.btf_struct_access	= bpf_mptcp_sched_btf_struct_access,
+};
+
+static int bpf_mptcp_sched_reg(void *kdata, struct bpf_link *link)
+{
+	return mptcp_register_scheduler(kdata);
+}
+
+static void bpf_mptcp_sched_unreg(void *kdata, struct bpf_link *link)
+{
+	mptcp_unregister_scheduler(kdata);
+}
+
+static int bpf_mptcp_sched_check_member(const struct btf_type *t,
+					const struct btf_member *member,
+					const struct bpf_prog *prog)
+{
+	return 0;
+}
+
+static int bpf_mptcp_sched_init_member(const struct btf_type *t,
+				       const struct btf_member *member,
+				       void *kdata, const void *udata)
+{
+	const struct mptcp_sched_ops *usched;
+	struct mptcp_sched_ops *sched;
+	u32 moff;
+	int ret;
+
+	usched = (const struct mptcp_sched_ops *)udata;
+	sched = (struct mptcp_sched_ops *)kdata;
+
+	moff = __btf_member_bit_offset(t, member) / 8;
+	switch (moff) {
+	case offsetof(struct mptcp_sched_ops, name):
+		if (bpf_obj_name_cpy(sched->name, usched->name,
+				     sizeof(sched->name)) <= 0)
+			return -EINVAL;
+
+		rcu_read_lock();
+		ret = mptcp_sched_find(usched->name) ? -EEXIST : 1;
+		rcu_read_unlock();
+
+		return ret;
+	}
+
+	return 0;
+}
+
+static int bpf_mptcp_sched_init(struct btf *btf)
+{
+	s32 type_id;
+
+	type_id = btf_find_by_name_kind(btf, "mptcp_sock",
+					BTF_KIND_STRUCT);
+	if (type_id < 0)
+		return -EINVAL;
+	mptcp_sock_id = type_id;
+	mptcp_sock_type = btf_type_by_id(btf, mptcp_sock_id);
+
+	type_id = btf_find_by_name_kind(btf, "mptcp_subflow_context",
+					BTF_KIND_STRUCT);
+	if (type_id < 0)
+		return -EINVAL;
+	mptcp_subflow_id = type_id;
+	mptcp_subflow_type = btf_type_by_id(btf, mptcp_subflow_id);
+
+	return 0;
+}
+
+static int __bpf_mptcp_sched_get_send(struct mptcp_sock *msk)
+{
+	return 0;
+}
+
+static int __bpf_mptcp_sched_get_retrans(struct mptcp_sock *msk)
+{
+	return 0;
+}
+
+static void __bpf_mptcp_sched_init(struct mptcp_sock *msk)
+{
+}
+
+static void __bpf_mptcp_sched_release(struct mptcp_sock *msk)
+{
+}
+
+static struct mptcp_sched_ops __bpf_mptcp_sched_ops = {
+	.get_send	= __bpf_mptcp_sched_get_send,
+	.get_retrans	= __bpf_mptcp_sched_get_retrans,
+	.init		= __bpf_mptcp_sched_init,
+	.release	= __bpf_mptcp_sched_release,
+};
+
+static struct bpf_struct_ops bpf_mptcp_sched_ops = {
+	.verifier_ops	= &bpf_mptcp_sched_verifier_ops,
+	.reg		= bpf_mptcp_sched_reg,
+	.unreg		= bpf_mptcp_sched_unreg,
+	.check_member	= bpf_mptcp_sched_check_member,
+	.init_member	= bpf_mptcp_sched_init_member,
+	.init		= bpf_mptcp_sched_init,
+	.name		= "mptcp_sched_ops",
+	.cfi_stubs	= &__bpf_mptcp_sched_ops,
+};
+#endif /* CONFIG_BPF_JIT */
+
 struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 {
 	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
@@ -115,6 +296,9 @@ static int __init bpf_mptcp_kfunc_init(void)
 	ret = register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCKOPT,
 					       &bpf_mptcp_common_kfunc_set);
+#ifdef CONFIG_BPF_JIT
+	ret = ret ?: register_bpf_struct_ops(&bpf_mptcp_sched_ops, mptcp_sched_ops);
+#endif
 
 	return ret;
 }