[RFC PATCH bpf-next 04/14] xdp_flow: Attach bpf prog to XDP in kernel after UMH loaded program

[Toshiaki Makita <toshiaki.makita1@gmail.com>]

As UMH runs under RTNL, it cannot attach XDP from userspace. Thus the
kernel, xdp_flow module, installs the XDP program.

NOTE: As an RFC, XDP-related logic is emulating dev_change_xdp_fd().
I'm thinking I should factor out the logic from dev_change_xdp_fd() and
export it instead.

Signed-off-by: Toshiaki Makita <toshiaki.makita1@gmail.com>
---
 include/linux/netdevice.h        |  4 +++
 net/core/dev.c                   | 11 ++++---
 net/xdp_flow/xdp_flow_kern_mod.c | 63 ++++++++++++++++++++++++++++++++++++----
 3 files changed, 69 insertions(+), 9 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 8829295..c99e022 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3678,6 +3678,10 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 				    struct netdev_queue *txq, int *ret);
 
 typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf *bpf);
+int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
+		    struct netlink_ext_ack *extack, u32 flags,
+		    struct bpf_prog *prog);
+int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp);
 int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		      int fd, u32 flags);
 u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
diff --git a/net/core/dev.c b/net/core/dev.c
index fc676b2..a45d2e4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5145,7 +5145,7 @@ static void __netif_receive_skb_list(struct list_head *head)
 		memalloc_noreclaim_restore(noreclaim_flag);
 }
 
-static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
+int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 {
 	struct bpf_prog *old = rtnl_dereference(dev->xdp_prog);
 	struct bpf_prog *new = xdp->prog;
@@ -5177,6 +5177,7 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(generic_xdp_install);
 
 static int netif_receive_skb_internal(struct sk_buff *skb)
 {
@@ -8001,10 +8002,11 @@ u32 __dev_xdp_query(struct net_device *dev, bpf_op_t bpf_op,
 
 	return xdp.prog_id;
 }
+EXPORT_SYMBOL_GPL(__dev_xdp_query);
 
-static int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
-			   struct netlink_ext_ack *extack, u32 flags,
-			   struct bpf_prog *prog)
+int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
+		    struct netlink_ext_ack *extack, u32 flags,
+		    struct bpf_prog *prog)
 {
 	struct netdev_bpf xdp;
 
@@ -8019,6 +8021,7 @@ static int dev_xdp_install(struct net_device *dev, bpf_op_t bpf_op,
 
 	return bpf_op(dev, &xdp);
 }
+EXPORT_SYMBOL_GPL(dev_xdp_install);
 
 static void dev_xdp_uninstall(struct net_device *dev)
 {
diff --git a/net/xdp_flow/xdp_flow_kern_mod.c b/net/xdp_flow/xdp_flow_kern_mod.c
index 823ab65..9cf527d 100644
--- a/net/xdp_flow/xdp_flow_kern_mod.c
+++ b/net/xdp_flow/xdp_flow_kern_mod.c
@@ -116,10 +116,26 @@ static int xdp_flow_setup_block_cb(enum tc_setup_type type, void *type_data,
 static int xdp_flow_setup_bind(struct net_device *dev,
 			       struct netlink_ext_ack *extack)
 {
+	enum bpf_prog_type attach_type = BPF_PROG_TYPE_XDP;
 	struct mbox_request *req;
+	bpf_op_t bpf_op, bpf_chk;
+	struct bpf_prog *prog;
 	u32 id = 0;
 	int err;
 
+	bpf_op = bpf_chk = dev->netdev_ops->ndo_bpf;
+	if (!bpf_op)
+		bpf_op = generic_xdp_install;
+	else
+		bpf_chk = generic_xdp_install;
+
+	/* TODO: These checks should be unified with net core */
+	if (__dev_xdp_query(dev, bpf_chk, XDP_QUERY_PROG))
+		return -EEXIST;
+
+	if (__dev_xdp_query(dev, bpf_op, XDP_QUERY_PROG))
+		return -EBUSY;
+
 	req = kzalloc(sizeof(*req), GFP_KERNEL);
 	if (!req)
 		return -ENOMEM;
@@ -129,21 +145,56 @@ static int xdp_flow_setup_bind(struct net_device *dev,
 
 	/* Load bpf in UMH and get prog id */
 	err = transact_umh(req, &id);
+	if (err)
+		goto out;
+
+	prog = bpf_prog_get_by_id(id);
+	if (IS_ERR(prog)) {
+		err = PTR_ERR(prog);
+		goto err_umh;
+	}
+
+	if (!bpf_prog_get_ok(prog, &attach_type, false)) {
+		err = -EINVAL;
+		goto err_prog;
+	}
 
-	/* TODO: id will be used to attach bpf prog to XDP
-	 * As we have rtnl_lock, UMH cannot attach prog to XDP
-	 */
+	/* As we have rtnl_lock, install XDP in kernel */
+	err = dev_xdp_install(dev, bpf_op, extack, 0, prog);
+	if (err)
+		goto err_prog;
 
+	/* TODO: Should get prog once more and save it for later check */
+out:
 	kfree(req);
 
 	return err;
+err_prog:
+	bpf_prog_put(prog);
+err_umh:
+	req->cmd = XDP_FLOW_CMD_UNLOAD;
+	transact_umh(req, NULL);
+
+	goto out;
 }
 
 static int xdp_flow_setup_unbind(struct net_device *dev,
 				 struct netlink_ext_ack *extack)
 {
 	struct mbox_request *req;
-	int err;
+	int err, ret = 0;
+	bpf_op_t bpf_op;
+
+	bpf_op = dev->netdev_ops->ndo_bpf;
+	if (!bpf_op)
+		bpf_op = generic_xdp_install;
+
+	/* TODO: Should check if prog is not changed */
+	err = dev_xdp_install(dev, bpf_op, extack, 0, NULL);
+	if (err) {
+		pr_warn("Failed to uninstall XDP prog: %d\n", err);
+		ret = err;
+	}
 
 	req = kzalloc(sizeof(*req), GFP_KERNEL);
 	if (!req)
@@ -153,10 +204,12 @@ static int xdp_flow_setup_unbind(struct net_device *dev,
 	req->ifindex = dev->ifindex;
 
 	err = transact_umh(req, NULL);
+	if (err)
+		ret = err;
 
 	kfree(req);
 
-	return err;
+	return ret;
 }
 
 static int xdp_flow_setup(struct net_device *dev, bool do_bind,
-- 
1.8.3.1