tun: enable gso over UDP tunnel support.

Add new tun features to represent the newly introduced virtio
GSO over UDP tunnel offload. Allows detection and selection of
such features via the existing TUNSETOFFLOAD ioctl and compute
the expected virtio header size and tunnel header offset using
the current netdev features, so that we can plug almost seamless
the newly introduced virtio helpers to serialize the extended
virtio header.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v6 -> v7:
  - rebased

v4 -> v5:
  - encapsulate the guest feature guessing in a tun helper
  - dropped irrelevant check on xdp buff headroom
  - do not remove unrelated black line
  - avoid line len > 80 char

v3 -> v4:
  - virtio tnl-related fields are at fixed offset, cleanup
    the code accordingly.
  - use netdev features instead of flags bit to check for
    the configured offload
  - drop packet in case of enabled features/configured hdr
    size mismatch

v2 -> v3:
  - cleaned-up uAPI comments
  - use explicit struct layout instead of raw buf.

1 files changed, 49 insertions, 9 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f8c5e2fd04df..abc91f28dac4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -186,7 +186,8 @@ struct tun_struct {
 	struct net_device	*dev;
 	netdev_features_t	set_features;
 #define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
-			  NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4)
+			  NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4 | \
+			  NETIF_F_GSO_UDP_TUNNEL | NETIF_F_GSO_UDP_TUNNEL_CSUM)
 
 	int			align;
 	int			vnet_hdr_sz;
@@ -925,6 +926,7 @@ static int tun_net_init(struct net_device *dev)
 	dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
 			   TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
 			   NETIF_F_HW_VLAN_STAG_TX;
+	dev->hw_enc_features = dev->hw_features;
 	dev->features = dev->hw_features;
 	dev->vlan_features = dev->features &
 			     ~(NETIF_F_HW_VLAN_CTAG_TX |
@@ -1698,7 +1700,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	struct sk_buff *skb;
 	size_t total_len = iov_iter_count(from);
 	size_t len = total_len, align = tun->align, linear;
-	struct virtio_net_hdr gso = { 0 };
+	struct virtio_net_hdr_v1_hash_tunnel hdr;
+	struct virtio_net_hdr *gso;
 	int good_linear;
 	int copylen;
 	int hdr_len = 0;
@@ -1708,6 +1711,15 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	int skb_xdp = 1;
 	bool frags = tun_napi_frags_enabled(tfile);
 	enum skb_drop_reason drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
+	netdev_features_t features = 0;
+
+	/*
+	 * Keep it easy and always zero the whole buffer, even if the
+	 * tunnel-related field will be touched only when the feature
+	 * is enabled and the hdr size id compatible.
+	 */
+	memset(&hdr, 0, sizeof(hdr));
+	gso = (struct virtio_net_hdr *)&hdr;
 
 	if (!(tun->flags & IFF_NO_PI)) {
 		if (len < sizeof(pi))
@@ -1721,7 +1733,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	if (tun->flags & IFF_VNET_HDR) {
 		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
 
-		hdr_len = tun_vnet_hdr_get(vnet_hdr_sz, tun->flags, from, &gso);
+		features = tun_vnet_hdr_guest_features(vnet_hdr_sz);
+		hdr_len = __tun_vnet_hdr_get(vnet_hdr_sz, tun->flags,
+					     features, from, gso);
 		if (hdr_len < 0)
 			return hdr_len;
 
@@ -1755,7 +1769,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		 * (e.g gso or jumbo packet), we will do it at after
 		 * skb was created with generic XDP routine.
 		 */
-		skb = tun_build_skb(tun, tfile, from, &gso, len, &skb_xdp);
+		skb = tun_build_skb(tun, tfile, from, gso, len, &skb_xdp);
 		err = PTR_ERR_OR_ZERO(skb);
 		if (err)
 			goto drop;
@@ -1799,7 +1813,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		}
 	}
 
-	if (tun_vnet_hdr_to_skb(tun->flags, skb, &gso)) {
+	if (tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, &hdr)) {
 		atomic_long_inc(&tun->rx_frame_errors);
 		err = -EINVAL;
 		goto free_skb;
@@ -2050,13 +2064,21 @@ static ssize_t tun_put_user(struct tun_struct *tun,
 	}
 
 	if (vnet_hdr_sz) {
-		struct virtio_net_hdr gso;
+		struct virtio_net_hdr_v1_hash_tunnel hdr;
+		struct virtio_net_hdr *gso;
 
-		ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
+		ret = tun_vnet_hdr_tnl_from_skb(tun->flags, tun->dev, skb,
+						&hdr);
 		if (ret)
 			return ret;
 
-		ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
+		/*
+		 * Drop the packet if the configured header size is too small
+		 * WRT the enabled offloads.
+		 */
+		gso = (struct virtio_net_hdr *)&hdr;
+		ret = __tun_vnet_hdr_put(vnet_hdr_sz, tun->dev->features,
+					 iter, gso);
 		if (ret)
 			return ret;
 	}
@@ -2357,10 +2379,12 @@ static int tun_xdp_one(struct tun_struct *tun,
 {
 	unsigned int datasize = xdp->data_end - xdp->data;
 	struct tun_xdp_hdr *hdr = xdp->data_hard_start;
+	struct virtio_net_hdr_v1_hash_tunnel *tnl_hdr;
 	struct virtio_net_hdr *gso = &hdr->gso;
 	struct bpf_prog *xdp_prog;
 	struct sk_buff *skb = NULL;
 	struct sk_buff_head *queue;
+	netdev_features_t features;
 	u32 rxhash = 0, act;
 	int buflen = hdr->buflen;
 	int metasize = 0;
@@ -2426,7 +2450,9 @@ build:
 	if (metasize > 0)
 		skb_metadata_set(skb, metasize);
 
-	if (tun_vnet_hdr_to_skb(tun->flags, skb, gso)) {
+	features = tun_vnet_hdr_guest_features(READ_ONCE(tun->vnet_hdr_sz));
+	tnl_hdr = (struct virtio_net_hdr_v1_hash_tunnel *)gso;
+	if (tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, tnl_hdr)) {
 		atomic_long_inc(&tun->rx_frame_errors);
 		kfree_skb(skb);
 		ret = -EINVAL;
@@ -2812,6 +2838,8 @@ static void tun_get_iff(struct tun_struct *tun, struct ifreq *ifr)
 
 }
 
+#define PLAIN_GSO (NETIF_F_GSO_UDP_L4 | NETIF_F_TSO | NETIF_F_TSO6)
+
 /* This is like a cut-down ethtool ops, except done via tun fd so no
  * privs required. */
 static int set_offload(struct tun_struct *tun, unsigned long arg)
@@ -2841,6 +2869,18 @@ static int set_offload(struct tun_struct *tun, unsigned long arg)
 			features |= NETIF_F_GSO_UDP_L4;
 			arg &= ~(TUN_F_USO4 | TUN_F_USO6);
 		}
+
+		/*
+		 * Tunnel offload is allowed only if some plain offload is
+		 * available, too.
+		 */
+		if (features & PLAIN_GSO && arg & TUN_F_UDP_TUNNEL_GSO) {
+			features |= NETIF_F_GSO_UDP_TUNNEL;
+			if (arg & TUN_F_UDP_TUNNEL_GSO_CSUM)
+				features |= NETIF_F_GSO_UDP_TUNNEL_CSUM;
+			arg &= ~(TUN_F_UDP_TUNNEL_GSO |
+				 TUN_F_UDP_TUNNEL_GSO_CSUM);
+		}
 	}
 
 	/* This gives the user a way to test for new features in future by