net/tls: Add generic NIC offload infrastructure

This patch adds a generic infrastructure to offload TLS crypto to a
network device. It enables the kernel TLS socket to skip encryption
and authentication operations on the transmit side of the data path.
Leaving those computationally expensive operations to the NIC.

The NIC offload infrastructure builds TLS records and pushes them to
the TCP layer just like the SW KTLS implementation and using the same
API.
TCP segmentation is mostly unaffected. Currently the only exception is
that we prevent mixed SKBs where only part of the payload requires
offload. In the future we are likely to add a similar restriction
following a change cipher spec record.

The notable differences between SW KTLS and NIC offloaded TLS
implementations are as follows:
1. The offloaded implementation builds "plaintext TLS record", those
records contain plaintext instead of ciphertext and place holder bytes
instead of authentication tags.
2. The offloaded implementation maintains a mapping from TCP sequence
number to TLS records. Thus given a TCP SKB sent from a NIC offloaded
TLS socket, we can use the tls NIC offload infrastructure to obtain
enough context to encrypt the payload of the SKB.
A TLS record is released when the last byte of the record is ack'ed,
this is done through the new icsk_clean_acked callback.

The infrastructure should be extendable to support various NIC offload
implementations.  However it is currently written with the
implementation below in mind:
The NIC assumes that packets from each offloaded stream are sent as
plaintext and in-order. It keeps track of the TLS records in the TCP
stream. When a packet marked for offload is transmitted, the NIC
encrypts the payload in-place and puts authentication tags in the
relevant place holders.

The responsibility for handling out-of-order packets (i.e. TCP
retransmission, qdisc drops) falls on the netdev driver.

The netdev driver keeps track of the expected TCP SN from the NIC's
perspective.  If the next packet to transmit matches the expected TCP
SN, the driver advances the expected TCP SN, and transmits the packet
with TLS offload indication.

If the next packet to transmit does not match the expected TCP SN. The
driver calls the TLS layer to obtain the TLS record that includes the
TCP of the packet for transmission. Using this TLS record, the driver
posts a work entry on the transmit queue to reconstruct the NIC TLS
state required for the offload of the out-of-order packet. It updates
the expected TCP SN accordingly and transmits the now in-order packet.
The same queue is used for packet transmission and TLS context
reconstruction to avoid the need for flushing the transmit queue before
issuing the context reconstruction request.

Signed-off-by: Ilya Lesokhin <ilyal@mellanox.com>
Signed-off-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Aviad Yehezkel <aviadye@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tls.h

@@ -116,6 +116,37 @@ struct tls_sw_context_rx {
 	bool decrypted;
 };
 
+struct tls_record_info {
+	struct list_head list;
+	u32 end_seq;
+	int len;
+	int num_frags;
+	skb_frag_t frags[MAX_SKB_FRAGS];
+};
+
+struct tls_offload_context {
+	struct crypto_aead *aead_send;
+	spinlock_t lock;	/* protects records list */
+	struct list_head records_list;
+	struct tls_record_info *open_record;
+	struct tls_record_info *retransmit_hint;
+	u64 hint_record_sn;
+	u64 unacked_record_sn;
+
+	struct scatterlist sg_tx_data[MAX_SKB_FRAGS];
+	void (*sk_destruct)(struct sock *sk);
+	u8 driver_state[];
+	/* The TLS layer reserves room for driver specific state
+	 * Currently the belief is that there is not enough
+	 * driver specific state to justify another layer of indirection
+	 */
+#define TLS_DRIVER_STATE_SIZE (max_t(size_t, 8, sizeof(void *)))
+};
+
+#define TLS_OFFLOAD_CONTEXT_SIZE                                               \
+	(ALIGN(sizeof(struct tls_offload_context), sizeof(void *)) +           \
+	 TLS_DRIVER_STATE_SIZE)
+
 enum {
 	TLS_PENDING_CLOSED_RECORD
 };
@@ -195,9 +226,28 @@ ssize_t tls_sw_splice_read(struct socket *sock, loff_t *ppos,
 			   struct pipe_inode_info *pipe,
 			   size_t len, unsigned int flags);
 
-void tls_sk_destruct(struct sock *sk, struct tls_context *ctx);
-void tls_icsk_clean_acked(struct sock *sk);
+int tls_set_device_offload(struct sock *sk, struct tls_context *ctx);
+int tls_device_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
+int tls_device_sendpage(struct sock *sk, struct page *page,
+			int offset, size_t size, int flags);
+void tls_device_sk_destruct(struct sock *sk);
+void tls_device_init(void);
+void tls_device_cleanup(void);
+
+struct tls_record_info *tls_get_record(struct tls_offload_context *context,
+				       u32 seq, u64 *p_record_sn);
+
+static inline bool tls_record_is_start_marker(struct tls_record_info *rec)
+{
+	return rec->len == 0;
+}
+
+static inline u32 tls_record_start_seq(struct tls_record_info *rec)
+{
+	return rec->end_seq - rec->len;
+}
 
+void tls_sk_destruct(struct sock *sk, struct tls_context *ctx);
 int tls_push_sg(struct sock *sk, struct tls_context *ctx,
 		struct scatterlist *sg, u16 first_offset,
 		int flags);
@@ -234,6 +284,13 @@ static inline bool tls_is_pending_open_record(struct tls_context *tls_ctx)
 	return tls_ctx->pending_open_record_frags;
 }
 
+static inline bool tls_is_sk_tx_device_offloaded(struct sock *sk)
+{
+	return sk_fullsock(sk) &&
+	       /* matches smp_store_release in tls_set_device_offload */
+	       smp_load_acquire(&sk->sk_destruct) == &tls_device_sk_destruct;
+}
+
 static inline void tls_err_abort(struct sock *sk, int err)
 {
 	sk->sk_err = err;
@@ -329,4 +386,12 @@ int tls_proccess_cmsg(struct sock *sk, struct msghdr *msg,
 void tls_register_device(struct tls_device *device);
 void tls_unregister_device(struct tls_device *device);
 
+struct sk_buff *tls_validate_xmit_skb(struct sock *sk,
+				      struct net_device *dev,
+				      struct sk_buff *skb);
+
+int tls_sw_fallback_init(struct sock *sk,
+			 struct tls_offload_context *offload_ctx,
+			 struct tls_crypto_info *crypto_info);
+
 #endif /* _TLS_OFFLOAD_H */

net/tls/Kconfig

@@ -14,3 +14,13 @@ config TLS
 	encryption handling of the TLS protocol to be done in-kernel.
 
 	If unsure, say N.
+
+config TLS_DEVICE
+	bool "Transport Layer Security HW offload"
+	depends on TLS
+	select SOCK_VALIDATE_XMIT
+	default n
+	help
+	Enable kernel support for HW offload of the TLS protocol.
+
+	If unsure, say N.

net/tls/Makefile

@@ -5,3 +5,5 @@
 obj-$(CONFIG_TLS) += tls.o
 
 tls-y := tls_main.o tls_sw.o
+
+tls-$(CONFIG_TLS_DEVICE) += tls_device.o tls_device_fallback.o