[bpf-next,v6,03/11] bpf: net_sched: Support implementation of Qdisc_ops in bpf

Commit Message

Amery Hung March 19, 2025, 9:53 p.m. UTC

From: Amery Hung <[e-mail]>

The recent advancement in bpf such as allocated objects, bpf list and bpf
rbtree has provided powerful and flexible building blocks to realize
sophisticated packet scheduling algorithms. As struct_ops now supports
core operators in Qdisc_ops, start allowing qdisc to be implemented using
bpf struct_ops with this patch. Users can implement Qdisc_ops.{enqueue,
dequeue, init, reset, destroy} in bpf and register the qdisc dynamically
into the kernel.

Co-developed-by: Cong Wang <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Signed-off-by: Amery Hung <[e-mail]>
Acked-by: Cong Wang <[e-mail]>
Acked-by: Toke Høiland-Jørgensen <[e-mail]>
---
 net/sched/Kconfig       |  12 +++
 net/sched/Makefile      |   1 +
 net/sched/bpf_qdisc.c   | 232 ++++++++++++++++++++++++++++++++++++++++
 net/sched/sch_api.c     |   7 +-
 net/sched/sch_generic.c |   3 +-
 5 files changed, 251 insertions(+), 4 deletions(-)
 create mode 100644 net/sched/bpf_qdisc.c

Patch

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 8180d0c12fce..ccd0255da5a5 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -403,6 +403,18 @@  config NET_SCH_ETS
 
 	  If unsure, say N.
 
+config NET_SCH_BPF
+	bool "BPF-based Qdisc"
+	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
+	help
+	  This option allows BPF-based queueing disiplines. With BPF struct_ops,
+	  users can implement supported operators in Qdisc_ops using BPF programs.
+	  The queue holding skb can be built with BPF maps or graphs.
+
+	  Say Y here if you want to use BPF-based Qdisc.
+
+	  If unsure, say N.
+
 menuconfig NET_SCH_DEFAULT
 	bool "Allow override default queue discipline"
 	help
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 82c3f78ca486..904d784902d1 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -62,6 +62,7 @@  obj-$(CONFIG_NET_SCH_FQ_PIE)	+= sch_fq_pie.o
 obj-$(CONFIG_NET_SCH_CBS)	+= sch_cbs.o
 obj-$(CONFIG_NET_SCH_ETF)	+= sch_etf.o
 obj-$(CONFIG_NET_SCH_TAPRIO)	+= sch_taprio.o
+obj-$(CONFIG_NET_SCH_BPF)	+= bpf_qdisc.o
 
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
 obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o
diff --git a/net/sched/bpf_qdisc.c b/net/sched/bpf_qdisc.c
new file mode 100644
index 000000000000..7eca556a3782
--- /dev/null
+++ b/net/sched/bpf_qdisc.c
@@ -0,0 +1,232 @@ 
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/types.h>
+#include <linux/bpf_verifier.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/filter.h>
+#include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
+
+static struct bpf_struct_ops bpf_Qdisc_ops;
+
+struct bpf_sk_buff_ptr {
+	struct sk_buff *skb;
+};
+
+static int bpf_qdisc_init(struct btf *btf)
+{
+	return 0;
+}
+
+BTF_ID_LIST_SINGLE(bpf_qdisc_ids, struct, Qdisc)
+BTF_ID_LIST_SINGLE(bpf_sk_buff_ids, struct, sk_buff)
+BTF_ID_LIST_SINGLE(bpf_sk_buff_ptr_ids, struct, bpf_sk_buff_ptr)
+
+static bool bpf_qdisc_is_valid_access(int off, int size,
+				      enum bpf_access_type type,
+				      const struct bpf_prog *prog,
+				      struct bpf_insn_access_aux *info)
+{
+	struct btf *btf = prog->aux->attach_btf;
+	u32 arg;
+
+	arg = btf_ctx_arg_idx(btf, prog->aux->attach_func_proto, off);
+	if (prog->aux->attach_st_ops_member_off == offsetof(struct Qdisc_ops, enqueue)) {
+		if (arg == 2 && type == BPF_READ) {
+			info->reg_type = PTR_TO_BTF_ID | PTR_TRUSTED;
+			info->btf = btf;
+			info->btf_id = bpf_sk_buff_ptr_ids[0];
+			return true;
+		}
+	}
+
+	return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
+}
+
+static int bpf_qdisc_qdisc_access(struct bpf_verifier_log *log,
+				  const struct bpf_reg_state *reg,
+				  int off, size_t *end)
+{
+	switch (off) {
+	case offsetof(struct Qdisc, limit):
+		*end = offsetofend(struct Qdisc, limit);
+		break;
+	case offsetof(struct Qdisc, q) + offsetof(struct qdisc_skb_head, qlen):
+		*end = offsetof(struct Qdisc, q) + offsetofend(struct qdisc_skb_head, qlen);
+		break;
+	case offsetof(struct Qdisc, qstats) ... offsetofend(struct Qdisc, qstats) - 1:
+		*end = offsetofend(struct Qdisc, qstats);
+		break;
+	default:
+		return -EACCES;
+	}
+
+	return 0;
+}
+
+static int bpf_qdisc_sk_buff_access(struct bpf_verifier_log *log,
+				    const struct bpf_reg_state *reg,
+				    int off, size_t *end)
+{
+	switch (off) {
+	case offsetof(struct sk_buff, tstamp):
+		*end = offsetofend(struct sk_buff, tstamp);
+		break;
+	case offsetof(struct sk_buff, priority):
+		*end = offsetofend(struct sk_buff, priority);
+		break;
+	case offsetof(struct sk_buff, mark):
+		*end = offsetofend(struct sk_buff, mark);
+		break;
+	case offsetof(struct sk_buff, queue_mapping):
+		*end = offsetofend(struct sk_buff, queue_mapping);
+		break;
+	case offsetof(struct sk_buff, cb) + offsetof(struct qdisc_skb_cb, tc_classid):
+		*end = offsetof(struct sk_buff, cb) +
+		       offsetofend(struct qdisc_skb_cb, tc_classid);
+		break;
+	case offsetof(struct sk_buff, cb) + offsetof(struct qdisc_skb_cb, data[0]) ...
+	     offsetof(struct sk_buff, cb) + offsetof(struct qdisc_skb_cb,
+						     data[QDISC_CB_PRIV_LEN - 1]):
+		*end = offsetof(struct sk_buff, cb) +
+		       offsetofend(struct qdisc_skb_cb, data[QDISC_CB_PRIV_LEN - 1]);
+		break;
+	case offsetof(struct sk_buff, tc_index):
+		*end = offsetofend(struct sk_buff, tc_index);
+		break;
+	default:
+		return -EACCES;
+	}
+
+	return 0;
+}
+
+static int bpf_qdisc_btf_struct_access(struct bpf_verifier_log *log,
+				       const struct bpf_reg_state *reg,
+				       int off, int size)
+{
+	const struct btf_type *t, *skbt, *qdisct;
+	size_t end;
+	int err;
+
+	skbt = btf_type_by_id(reg->btf, bpf_sk_buff_ids[0]);
+	qdisct = btf_type_by_id(reg->btf, bpf_qdisc_ids[0]);
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+
+	if (t == skbt) {
+		err = bpf_qdisc_sk_buff_access(log, reg, off, &end);
+	} else if (t == qdisct) {
+		err = bpf_qdisc_qdisc_access(log, reg, off, &end);
+	} else {
+		bpf_log(log, "only read is supported\n");
+		return -EACCES;
+	}
+
+	if (err) {
+		bpf_log(log, "no write support to %s at off %d\n",
+			btf_name_by_offset(reg->btf, t->name_off), off);
+		return -EACCES;
+	}
+
+	if (off + size > end) {
+		bpf_log(log,
+			"write access at off %d with size %d beyond the member of %s ended at %zu\n",
+			off, size, btf_name_by_offset(reg->btf, t->name_off), end);
+		return -EACCES;
+	}
+
+	return 0;
+}
+
+static const struct bpf_verifier_ops bpf_qdisc_verifier_ops = {
+	.get_func_proto		= bpf_base_func_proto,
+	.is_valid_access	= bpf_qdisc_is_valid_access,
+	.btf_struct_access	= bpf_qdisc_btf_struct_access,
+};
+
+static int bpf_qdisc_init_member(const struct btf_type *t,
+				 const struct btf_member *member,
+				 void *kdata, const void *udata)
+{
+	const struct Qdisc_ops *uqdisc_ops;
+	struct Qdisc_ops *qdisc_ops;
+	u32 moff;
+
+	uqdisc_ops = (const struct Qdisc_ops *)udata;
+	qdisc_ops = (struct Qdisc_ops *)kdata;
+
+	moff = __btf_member_bit_offset(t, member) / 8;
+	switch (moff) {
+	case offsetof(struct Qdisc_ops, peek):
+		qdisc_ops->peek = qdisc_peek_dequeued;
+		return 0;
+	case offsetof(struct Qdisc_ops, id):
+		if (bpf_obj_name_cpy(qdisc_ops->id, uqdisc_ops->id,
+				     sizeof(qdisc_ops->id)) <= 0)
+			return -EINVAL;
+		return 1;
+	}
+
+	return 0;
+}
+
+static int bpf_qdisc_reg(void *kdata, struct bpf_link *link)
+{
+	return register_qdisc(kdata);
+}
+
+static void bpf_qdisc_unreg(void *kdata, struct bpf_link *link)
+{
+	return unregister_qdisc(kdata);
+}
+
+static int Qdisc_ops__enqueue(struct sk_buff *skb__ref, struct Qdisc *sch,
+			      struct sk_buff **to_free)
+{
+	return 0;
+}
+
+static struct sk_buff *Qdisc_ops__dequeue(struct Qdisc *sch)
+{
+	return NULL;
+}
+
+static int Qdisc_ops__init(struct Qdisc *sch, struct nlattr *arg,
+			   struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+static void Qdisc_ops__reset(struct Qdisc *sch)
+{
+}
+
+static void Qdisc_ops__destroy(struct Qdisc *sch)
+{
+}
+
+static struct Qdisc_ops __bpf_ops_qdisc_ops = {
+	.enqueue = Qdisc_ops__enqueue,
+	.dequeue = Qdisc_ops__dequeue,
+	.init = Qdisc_ops__init,
+	.reset = Qdisc_ops__reset,
+	.destroy = Qdisc_ops__destroy,
+};
+
+static struct bpf_struct_ops bpf_Qdisc_ops = {
+	.verifier_ops = &bpf_qdisc_verifier_ops,
+	.reg = bpf_qdisc_reg,
+	.unreg = bpf_qdisc_unreg,
+	.init_member = bpf_qdisc_init_member,
+	.init = bpf_qdisc_init,
+	.name = "Qdisc_ops",
+	.cfi_stubs = &__bpf_ops_qdisc_ops,
+	.owner = THIS_MODULE,
+};
+
+static int __init bpf_qdisc_kfunc_init(void)
+{
+	return register_bpf_struct_ops(&bpf_Qdisc_ops, Qdisc_ops);
+}
+late_initcall(bpf_qdisc_kfunc_init);
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index e3e91cf867eb..1aad41b7d5a8 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -25,6 +25,7 @@ 
 #include <linux/hrtimer.h>
 #include <linux/slab.h>
 #include <linux/hashtable.h>
+#include <linux/bpf.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -358,7 +359,7 @@  static struct Qdisc_ops *qdisc_lookup_ops(struct nlattr *kind)
 		read_lock(&qdisc_mod_lock);
 		for (q = qdisc_base; q; q = q->next) {
 			if (nla_strcmp(kind, q->id) == 0) {
-				if (!try_module_get(q->owner))
+				if (!bpf_try_module_get(q, q->owner))
 					q = NULL;
 				break;
 			}
@@ -1287,7 +1288,7 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 				/* We will try again qdisc_lookup_ops,
 				 * so don't keep a reference.
 				 */
-				module_put(ops->owner);
+				bpf_module_put(ops, ops->owner);
 				err = -EAGAIN;
 				goto err_out;
 			}
@@ -1398,7 +1399,7 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 	netdev_put(dev, &sch->dev_tracker);
 	qdisc_free(sch);
 err_out2:
-	module_put(ops->owner);
+	bpf_module_put(ops, ops->owner);
 err_out:
 	*errp = err;
 	return NULL;
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 14ab2f4c190a..e6fda9f20272 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -24,6 +24,7 @@ 
 #include <linux/if_vlan.h>
 #include <linux/skb_array.h>
 #include <linux/if_macvlan.h>
+#include <linux/bpf.h>
 #include <net/sch_generic.h>
 #include <net/pkt_sched.h>
 #include <net/dst.h>
@@ -1078,7 +1079,7 @@  static void __qdisc_destroy(struct Qdisc *qdisc)
 		ops->destroy(qdisc);
 
 	lockdep_unregister_key(&qdisc->root_lock_key);
-	module_put(ops->owner);
+	bpf_module_put(ops, ops->owner);
 	netdev_put(dev, &qdisc->dev_tracker);
 
 	trace_qdisc_destroy(qdisc);