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>

1 files changed, 450 insertions, 0 deletions

diff --git a/net/tls/tls_device_fallback.c b/net/tls/tls_device_fallback.c
new file mode 100644
index 000000000000..748914abdb60
--- /dev/null
+++ b/net/tls/tls_device_fallback.c
@@ -0,0 +1,450 @@
+/* Copyright (c) 2018, Mellanox Technologies All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include <net/tls.h>
+#include <crypto/aead.h>
+#include <crypto/scatterwalk.h>
+#include <net/ip6_checksum.h>
+
+static void chain_to_walk(struct scatterlist *sg, struct scatter_walk *walk)
+{
+	struct scatterlist *src = walk->sg;
+	int diff = walk->offset - src->offset;
+
+	sg_set_page(sg, sg_page(src),
+		    src->length - diff, walk->offset);
+
+	scatterwalk_crypto_chain(sg, sg_next(src), 0, 2);
+}
+
+static int tls_enc_record(struct aead_request *aead_req,
+			  struct crypto_aead *aead, char *aad,
+			  char *iv, __be64 rcd_sn,
+			  struct scatter_walk *in,
+			  struct scatter_walk *out, int *in_len)
+{
+	unsigned char buf[TLS_HEADER_SIZE + TLS_CIPHER_AES_GCM_128_IV_SIZE];
+	struct scatterlist sg_in[3];
+	struct scatterlist sg_out[3];
+	u16 len;
+	int rc;
+
+	len = min_t(int, *in_len, ARRAY_SIZE(buf));
+
+	scatterwalk_copychunks(buf, in, len, 0);
+	scatterwalk_copychunks(buf, out, len, 1);
+
+	*in_len -= len;
+	if (!*in_len)
+		return 0;
+
+	scatterwalk_pagedone(in, 0, 1);
+	scatterwalk_pagedone(out, 1, 1);
+
+	len = buf[4] | (buf[3] << 8);
+	len -= TLS_CIPHER_AES_GCM_128_IV_SIZE;
+
+	tls_make_aad(aad, len - TLS_CIPHER_AES_GCM_128_TAG_SIZE,
+		     (char *)&rcd_sn, sizeof(rcd_sn), buf[0]);
+
+	memcpy(iv + TLS_CIPHER_AES_GCM_128_SALT_SIZE, buf + TLS_HEADER_SIZE,
+	       TLS_CIPHER_AES_GCM_128_IV_SIZE);
+
+	sg_init_table(sg_in, ARRAY_SIZE(sg_in));
+	sg_init_table(sg_out, ARRAY_SIZE(sg_out));
+	sg_set_buf(sg_in, aad, TLS_AAD_SPACE_SIZE);
+	sg_set_buf(sg_out, aad, TLS_AAD_SPACE_SIZE);
+	chain_to_walk(sg_in + 1, in);
+	chain_to_walk(sg_out + 1, out);
+
+	*in_len -= len;
+	if (*in_len < 0) {
+		*in_len += TLS_CIPHER_AES_GCM_128_TAG_SIZE;
+		/* the input buffer doesn't contain the entire record.
+		 * trim len accordingly. The resulting authentication tag
+		 * will contain garbage, but we don't care, so we won't
+		 * include any of it in the output skb
+		 * Note that we assume the output buffer length
+		 * is larger then input buffer length + tag size
+		 */
+		if (*in_len < 0)
+			len += *in_len;
+
+		*in_len = 0;
+	}
+
+	if (*in_len) {
+		scatterwalk_copychunks(NULL, in, len, 2);
+		scatterwalk_pagedone(in, 0, 1);
+		scatterwalk_copychunks(NULL, out, len, 2);
+		scatterwalk_pagedone(out, 1, 1);
+	}
+
+	len -= TLS_CIPHER_AES_GCM_128_TAG_SIZE;
+	aead_request_set_crypt(aead_req, sg_in, sg_out, len, iv);
+
+	rc = crypto_aead_encrypt(aead_req);
+
+	return rc;
+}
+
+static void tls_init_aead_request(struct aead_request *aead_req,
+				  struct crypto_aead *aead)
+{
+	aead_request_set_tfm(aead_req, aead);
+	aead_request_set_ad(aead_req, TLS_AAD_SPACE_SIZE);
+}
+
+static struct aead_request *tls_alloc_aead_request(struct crypto_aead *aead,
+						   gfp_t flags)
+{
+	unsigned int req_size = sizeof(struct aead_request) +
+		crypto_aead_reqsize(aead);
+	struct aead_request *aead_req;
+
+	aead_req = kzalloc(req_size, flags);
+	if (aead_req)
+		tls_init_aead_request(aead_req, aead);
+	return aead_req;
+}
+
+static int tls_enc_records(struct aead_request *aead_req,
+			   struct crypto_aead *aead, struct scatterlist *sg_in,
+			   struct scatterlist *sg_out, char *aad, char *iv,
+			   u64 rcd_sn, int len)
+{
+	struct scatter_walk out, in;
+	int rc;
+
+	scatterwalk_start(&in, sg_in);
+	scatterwalk_start(&out, sg_out);
+
+	do {
+		rc = tls_enc_record(aead_req, aead, aad, iv,
+				    cpu_to_be64(rcd_sn), &in, &out, &len);
+		rcd_sn++;
+
+	} while (rc == 0 && len);
+
+	scatterwalk_done(&in, 0, 0);
+	scatterwalk_done(&out, 1, 0);
+
+	return rc;
+}
+
+/* Can't use icsk->icsk_af_ops->send_check here because the ip addresses
+ * might have been changed by NAT.
+ */
+static void update_chksum(struct sk_buff *skb, int headln)
+{
+	struct tcphdr *th = tcp_hdr(skb);
+	int datalen = skb->len - headln;
+	const struct ipv6hdr *ipv6h;
+	const struct iphdr *iph;
+
+	/* We only changed the payload so if we are using partial we don't
+	 * need to update anything.
+	 */
+	if (likely(skb->ip_summed == CHECKSUM_PARTIAL))
+		return;
+
+	skb->ip_summed = CHECKSUM_PARTIAL;
+	skb->csum_start = skb_transport_header(skb) - skb->head;
+	skb->csum_offset = offsetof(struct tcphdr, check);
+
+	if (skb->sk->sk_family == AF_INET6) {
+		ipv6h = ipv6_hdr(skb);
+		th->check = ~csum_ipv6_magic(&ipv6h->saddr, &ipv6h->daddr,
+					     datalen, IPPROTO_TCP, 0);
+	} else {
+		iph = ip_hdr(skb);
+		th->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, datalen,
+					       IPPROTO_TCP, 0);
+	}
+}
+
+static void complete_skb(struct sk_buff *nskb, struct sk_buff *skb, int headln)
+{
+	skb_copy_header(nskb, skb);
+
+	skb_put(nskb, skb->len);
+	memcpy(nskb->data, skb->data, headln);
+	update_chksum(nskb, headln);
+
+	nskb->destructor = skb->destructor;
+	nskb->sk = skb->sk;
+	skb->destructor = NULL;
+	skb->sk = NULL;
+	refcount_add(nskb->truesize - skb->truesize,
+		     &nskb->sk->sk_wmem_alloc);
+}
+
+/* This function may be called after the user socket is already
+ * closed so make sure we don't use anything freed during
+ * tls_sk_proto_close here
+ */
+
+static int fill_sg_in(struct scatterlist *sg_in,
+		      struct sk_buff *skb,
+		      struct tls_offload_context *ctx,
+		      u64 *rcd_sn,
+		      s32 *sync_size,
+		      int *resync_sgs)
+{
+	int tcp_payload_offset = skb_transport_offset(skb) + tcp_hdrlen(skb);
+	int payload_len = skb->len - tcp_payload_offset;
+	u32 tcp_seq = ntohl(tcp_hdr(skb)->seq);
+	struct tls_record_info *record;
+	unsigned long flags;
+	int remaining;
+	int i;
+
+	spin_lock_irqsave(&ctx->lock, flags);
+	record = tls_get_record(ctx, tcp_seq, rcd_sn);
+	if (!record) {
+		spin_unlock_irqrestore(&ctx->lock, flags);
+		WARN(1, "Record not found for seq %u\n", tcp_seq);
+		return -EINVAL;
+	}
+
+	*sync_size = tcp_seq - tls_record_start_seq(record);
+	if (*sync_size < 0) {
+		int is_start_marker = tls_record_is_start_marker(record);
+
+		spin_unlock_irqrestore(&ctx->lock, flags);
+		/* This should only occur if the relevant record was
+		 * already acked. In that case it should be ok
+		 * to drop the packet and avoid retransmission.
+		 *
+		 * There is a corner case where the packet contains
+		 * both an acked and a non-acked record.
+		 * We currently don't handle that case and rely
+		 * on TCP to retranmit a packet that doesn't contain
+		 * already acked payload.
+		 */
+		if (!is_start_marker)
+			*sync_size = 0;
+		return -EINVAL;
+	}
+
+	remaining = *sync_size;
+	for (i = 0; remaining > 0; i++) {
+		skb_frag_t *frag = &record->frags[i];
+
+		__skb_frag_ref(frag);
+		sg_set_page(sg_in + i, skb_frag_page(frag),
+			    skb_frag_size(frag), frag->page_offset);
+
+		remaining -= skb_frag_size(frag);
+
+		if (remaining < 0)
+			sg_in[i].length += remaining;
+	}
+	*resync_sgs = i;
+
+	spin_unlock_irqrestore(&ctx->lock, flags);
+	if (skb_to_sgvec(skb, &sg_in[i], tcp_payload_offset, payload_len) < 0)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void fill_sg_out(struct scatterlist sg_out[3], void *buf,
+			struct tls_context *tls_ctx,
+			struct sk_buff *nskb,
+			int tcp_payload_offset,
+			int payload_len,
+			int sync_size,
+			void *dummy_buf)
+{
+	sg_set_buf(&sg_out[0], dummy_buf, sync_size);
+	sg_set_buf(&sg_out[1], nskb->data + tcp_payload_offset, payload_len);
+	/* Add room for authentication tag produced by crypto */
+	dummy_buf += sync_size;
+	sg_set_buf(&sg_out[2], dummy_buf, TLS_CIPHER_AES_GCM_128_TAG_SIZE);
+}
+
+static struct sk_buff *tls_enc_skb(struct tls_context *tls_ctx,
+				   struct scatterlist sg_out[3],
+				   struct scatterlist *sg_in,
+				   struct sk_buff *skb,
+				   s32 sync_size, u64 rcd_sn)
+{
+	int tcp_payload_offset = skb_transport_offset(skb) + tcp_hdrlen(skb);
+	struct tls_offload_context *ctx = tls_offload_ctx(tls_ctx);
+	int payload_len = skb->len - tcp_payload_offset;
+	void *buf, *iv, *aad, *dummy_buf;
+	struct aead_request *aead_req;
+	struct sk_buff *nskb = NULL;
+	int buf_len;
+
+	aead_req = tls_alloc_aead_request(ctx->aead_send, GFP_ATOMIC);
+	if (!aead_req)
+		return NULL;
+
+	buf_len = TLS_CIPHER_AES_GCM_128_SALT_SIZE +
+		  TLS_CIPHER_AES_GCM_128_IV_SIZE +
+		  TLS_AAD_SPACE_SIZE +
+		  sync_size +
+		  TLS_CIPHER_AES_GCM_128_TAG_SIZE;
+	buf = kmalloc(buf_len, GFP_ATOMIC);
+	if (!buf)
+		goto free_req;
+
+	iv = buf;
+	memcpy(iv, tls_ctx->crypto_send_aes_gcm_128.salt,
+	       TLS_CIPHER_AES_GCM_128_SALT_SIZE);
+	aad = buf + TLS_CIPHER_AES_GCM_128_SALT_SIZE +
+	      TLS_CIPHER_AES_GCM_128_IV_SIZE;
+	dummy_buf = aad + TLS_AAD_SPACE_SIZE;
+
+	nskb = alloc_skb(skb_headroom(skb) + skb->len, GFP_ATOMIC);
+	if (!nskb)
+		goto free_buf;
+
+	skb_reserve(nskb, skb_headroom(skb));
+
+	fill_sg_out(sg_out, buf, tls_ctx, nskb, tcp_payload_offset,
+		    payload_len, sync_size, dummy_buf);
+
+	if (tls_enc_records(aead_req, ctx->aead_send, sg_in, sg_out, aad, iv,
+			    rcd_sn, sync_size + payload_len) < 0)
+		goto free_nskb;
+
+	complete_skb(nskb, skb, tcp_payload_offset);
+
+	/* validate_xmit_skb_list assumes that if the skb wasn't segmented
+	 * nskb->prev will point to the skb itself
+	 */
+	nskb->prev = nskb;
+
+free_buf:
+	kfree(buf);
+free_req:
+	kfree(aead_req);
+	return nskb;
+free_nskb:
+	kfree_skb(nskb);
+	nskb = NULL;
+	goto free_buf;
+}
+
+static struct sk_buff *tls_sw_fallback(struct sock *sk, struct sk_buff *skb)
+{
+	int tcp_payload_offset = skb_transport_offset(skb) + tcp_hdrlen(skb);
+	struct tls_context *tls_ctx = tls_get_ctx(sk);
+	struct tls_offload_context *ctx = tls_offload_ctx(tls_ctx);
+	int payload_len = skb->len - tcp_payload_offset;
+	struct scatterlist *sg_in, sg_out[3];
+	struct sk_buff *nskb = NULL;
+	int sg_in_max_elements;
+	int resync_sgs = 0;
+	s32 sync_size = 0;
+	u64 rcd_sn;
+
+	/* worst case is:
+	 * MAX_SKB_FRAGS in tls_record_info
+	 * MAX_SKB_FRAGS + 1 in SKB head and frags.
+	 */
+	sg_in_max_elements = 2 * MAX_SKB_FRAGS + 1;
+
+	if (!payload_len)
+		return skb;
+
+	sg_in = kmalloc_array(sg_in_max_elements, sizeof(*sg_in), GFP_ATOMIC);
+	if (!sg_in)
+		goto free_orig;
+
+	sg_init_table(sg_in, sg_in_max_elements);
+	sg_init_table(sg_out, ARRAY_SIZE(sg_out));
+
+	if (fill_sg_in(sg_in, skb, ctx, &rcd_sn, &sync_size, &resync_sgs)) {
+		/* bypass packets before kernel TLS socket option was set */
+		if (sync_size < 0 && payload_len <= -sync_size)
+			nskb = skb_get(skb);
+		goto put_sg;
+	}
+
+	nskb = tls_enc_skb(tls_ctx, sg_out, sg_in, skb, sync_size, rcd_sn);
+
+put_sg:
+	while (resync_sgs)
+		put_page(sg_page(&sg_in[--resync_sgs]));
+	kfree(sg_in);
+free_orig:
+	kfree_skb(skb);
+	return nskb;
+}
+
+struct sk_buff *tls_validate_xmit_skb(struct sock *sk,
+				      struct net_device *dev,
+				      struct sk_buff *skb)
+{
+	if (dev == tls_get_ctx(sk)->netdev)
+		return skb;
+
+	return tls_sw_fallback(sk, skb);
+}
+
+int tls_sw_fallback_init(struct sock *sk,
+			 struct tls_offload_context *offload_ctx,
+			 struct tls_crypto_info *crypto_info)
+{
+	const u8 *key;
+	int rc;
+
+	offload_ctx->aead_send =
+	    crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(offload_ctx->aead_send)) {
+		rc = PTR_ERR(offload_ctx->aead_send);
+		pr_err_ratelimited("crypto_alloc_aead failed rc=%d\n", rc);
+		offload_ctx->aead_send = NULL;
+		goto err_out;
+	}
+
+	key = ((struct tls12_crypto_info_aes_gcm_128 *)crypto_info)->key;
+
+	rc = crypto_aead_setkey(offload_ctx->aead_send, key,
+				TLS_CIPHER_AES_GCM_128_KEY_SIZE);
+	if (rc)
+		goto free_aead;
+
+	rc = crypto_aead_setauthsize(offload_ctx->aead_send,
+				     TLS_CIPHER_AES_GCM_128_TAG_SIZE);
+	if (rc)
+		goto free_aead;
+
+	return 0;
+free_aead:
+	crypto_free_aead(offload_ctx->aead_send);
+err_out:
+	return rc;
+}