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Subject[PATCH net-next V3] tun: add eBPF based queue selection method
Date
This patch introduces an eBPF based queue selection method. With this,
the policy could be offloaded to userspace completely through a new
ioctl TUNSETSTEERINGEBPF.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes from V2:
- call rtnl during netdev free
- switch to use call_rcu() to prevent DOS from userspace
- drop the policies setting/getting ioctls and allow detach through
passing -1 as fd
---
drivers/net/tun.c | 145 +++++++++++++++++++++++++++++++++++++-------
include/uapi/linux/if_tun.h | 1 +
2 files changed, 123 insertions(+), 23 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 9574900..f6557e8 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -195,6 +195,11 @@ struct tun_flow_entry {

#define TUN_NUM_FLOW_ENTRIES 1024

+struct tun_steering_prog {
+ struct rcu_head rcu;
+ struct bpf_prog *prog;
+};
+
/* Since the socket were moved to tun_file, to preserve the behavior of persist
* device, socket filter, sndbuf and vnet header size were restore when the
* file were attached to a persist device.
@@ -232,6 +237,7 @@ struct tun_struct {
u32 rx_batched;
struct tun_pcpu_stats __percpu *pcpu_stats;
struct bpf_prog __rcu *xdp_prog;
+ struct tun_steering_prog __rcu *steering_prog;
};

static int tun_napi_receive(struct napi_struct *napi, int budget)
@@ -537,15 +543,12 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
* different rxq no. here. If we could not get rxhash, then we would
* hope the rxq no. may help here.
*/
-static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
- void *accel_priv, select_queue_fallback_t fallback)
+static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
{
- struct tun_struct *tun = netdev_priv(dev);
struct tun_flow_entry *e;
u32 txq = 0;
u32 numqueues = 0;

- rcu_read_lock();
numqueues = READ_ONCE(tun->numqueues);

txq = __skb_get_hash_symmetric(skb);
@@ -563,10 +566,37 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
txq -= numqueues;
}

- rcu_read_unlock();
return txq;
}

+static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
+{
+ struct tun_steering_prog *prog;
+ u16 ret = 0;
+
+ prog = rcu_dereference(tun->steering_prog);
+ if (prog)
+ ret = bpf_prog_run_clear_cb(prog->prog, skb);
+
+ return ret % tun->numqueues;
+}
+
+static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
+ void *accel_priv, select_queue_fallback_t fallback)
+{
+ struct tun_struct *tun = netdev_priv(dev);
+ u16 ret;
+
+ rcu_read_lock();
+ if (rcu_dereference(tun->steering_prog))
+ ret = tun_ebpf_select_queue(tun, skb);
+ else
+ ret = tun_automq_select_queue(tun, skb);
+ rcu_read_unlock();
+
+ return ret;
+}
+
static inline bool tun_not_capable(struct tun_struct *tun)
{
const struct cred *cred = current_cred();
@@ -937,23 +967,10 @@ static int tun_net_close(struct net_device *dev)
}

/* Net device start xmit */
-static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
+static void tun_automq_xmit(struct tun_struct *tun, struct sk_buff *skb)
{
- struct tun_struct *tun = netdev_priv(dev);
- int txq = skb->queue_mapping;
- struct tun_file *tfile;
- u32 numqueues = 0;
-
- rcu_read_lock();
- tfile = rcu_dereference(tun->tfiles[txq]);
- numqueues = READ_ONCE(tun->numqueues);
-
- /* Drop packet if interface is not attached */
- if (txq >= numqueues)
- goto drop;
-
#ifdef CONFIG_RPS
- if (numqueues == 1 && static_key_false(&rps_needed)) {
+ if (tun->numqueues == 1 && static_key_false(&rps_needed)) {
/* Select queue was not called for the skbuff, so we extract the
* RPS hash and save it into the flow_table here.
*/
@@ -969,6 +986,26 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
}
}
#endif
+}
+
+/* Net device start xmit */
+static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+ struct tun_struct *tun = netdev_priv(dev);
+ int txq = skb->queue_mapping;
+ struct tun_file *tfile;
+ u32 numqueues = 0;
+
+ rcu_read_lock();
+ tfile = rcu_dereference(tun->tfiles[txq]);
+ numqueues = READ_ONCE(tun->numqueues);
+
+ /* Drop packet if interface is not attached */
+ if (txq >= numqueues)
+ goto drop;
+
+ if (!rcu_dereference(tun->steering_prog))
+ tun_automq_xmit(tun, skb);

tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", skb->len);

@@ -1551,7 +1588,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
int copylen;
bool zerocopy = false;
int err;
- u32 rxhash;
+ u32 rxhash = 0;
int skb_xdp = 1;
bool frags = tun_napi_frags_enabled(tun);

@@ -1739,7 +1776,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
rcu_read_unlock();
}

- rxhash = __skb_get_hash_symmetric(skb);
+ rcu_read_lock();
+ if (!rcu_dereference(tun->steering_prog))
+ rxhash = __skb_get_hash_symmetric(skb);
+ rcu_read_unlock();

if (frags) {
/* Exercise flow dissector code path. */
@@ -1783,7 +1823,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
u64_stats_update_end(&stats->syncp);
put_cpu_ptr(stats);

- tun_flow_update(tun, rxhash, tfile);
+ if (rxhash)
+ tun_flow_update(tun, rxhash, tfile);
+
return total_len;
}

@@ -1988,6 +2030,36 @@ static ssize_t tun_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
return ret;
}

+static void tun_steering_prog_free(struct rcu_head *rcu)
+{
+ struct tun_steering_prog *prog = container_of(rcu,
+ struct tun_steering_prog, rcu);
+
+ bpf_prog_destroy(prog->prog);
+ kfree(prog);
+}
+
+static int __tun_set_steering_ebpf(struct tun_struct *tun,
+ struct bpf_prog *prog)
+{
+ struct tun_steering_prog *old, *new = NULL;
+
+ if (prog) {
+ new = kmalloc(sizeof(*new), GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+ new->prog = prog;
+ }
+
+ old = rtnl_dereference(tun->steering_prog);
+ rcu_assign_pointer(tun->steering_prog, new);
+
+ if (old)
+ call_rcu(&old->rcu, tun_steering_prog_free);
+
+ return 0;
+}
+
static void tun_free_netdev(struct net_device *dev)
{
struct tun_struct *tun = netdev_priv(dev);
@@ -1996,6 +2068,9 @@ static void tun_free_netdev(struct net_device *dev)
free_percpu(tun->pcpu_stats);
tun_flow_uninit(tun);
security_tun_dev_free_security(tun->security);
+ rtnl_lock();
+ __tun_set_steering_ebpf(tun, NULL);
+ rtnl_unlock();
}

static void tun_setup(struct net_device *dev)
@@ -2275,6 +2350,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
tun->filter_attached = false;
tun->sndbuf = tfile->socket.sk->sk_sndbuf;
tun->rx_batched = 0;
+ RCU_INIT_POINTER(tun->steering_prog, NULL);

tun->pcpu_stats = netdev_alloc_pcpu_stats(struct tun_pcpu_stats);
if (!tun->pcpu_stats) {
@@ -2467,6 +2543,25 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
return ret;
}

+static int tun_set_steering_ebpf(struct tun_struct *tun, void __user *data)
+{
+ struct bpf_prog *prog;
+ int fd;
+
+ if (copy_from_user(&fd, data, sizeof(fd)))
+ return -EFAULT;
+
+ if (fd == -1) {
+ prog = NULL;
+ } else {
+ prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
+ if (IS_ERR(prog))
+ return PTR_ERR(prog);
+ }
+
+ return __tun_set_steering_ebpf(tun, prog);
+}
+
static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
unsigned long arg, int ifreq_len)
{
@@ -2743,6 +2838,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
ret = 0;
break;

+ case TUNSETSTEERINGEBPF:
+ ret = tun_set_steering_ebpf(tun, argp);
+ break;
+
default:
ret = -EINVAL;
break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 030d3e6..fb38c17 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -57,6 +57,7 @@
*/
#define TUNSETVNETBE _IOW('T', 222, int)
#define TUNGETVNETBE _IOR('T', 223, int)
+#define TUNSETSTEERINGEBPF _IOR('T', 224, int)

/* TUNSETIFF ifr flags */
#define IFF_TUN 0x0001
--
2.7.4
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