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c4a0eb93 | 1 | .. SPDX-License-Identifier: GPL-2.0 |
5c0bb261 SN |
2 | |
3 | =============================================== | |
4 | XFRM device - offloading the IPsec computations | |
5 | =============================================== | |
c4a0eb93 | 6 | |
5c0bb261 | 7 | Shannon Nelson <shannon.nelson@oracle.com> |
2b7c72e0 | 8 | Leon Romanovsky <leonro@nvidia.com> |
5c0bb261 SN |
9 | |
10 | ||
11 | Overview | |
12 | ======== | |
13 | ||
14 | IPsec is a useful feature for securing network traffic, but the | |
15 | computational cost is high: a 10Gbps link can easily be brought down | |
16 | to under 1Gbps, depending on the traffic and link configuration. | |
17 | Luckily, there are NICs that offer a hardware based IPsec offload which | |
18 | can radically increase throughput and decrease CPU utilization. The XFRM | |
19 | Device interface allows NIC drivers to offer to the stack access to the | |
20 | hardware offload. | |
21 | ||
2b7c72e0 LR |
22 | Right now, there are two types of hardware offload that kernel supports. |
23 | * IPsec crypto offload: | |
24 | * NIC performs encrypt/decrypt | |
25 | * Kernel does everything else | |
26 | * IPsec packet offload: | |
27 | * NIC performs encrypt/decrypt | |
28 | * NIC does encapsulation | |
29 | * Kernel and NIC have SA and policy in-sync | |
30 | * NIC handles the SA and policies states | |
31 | * The Kernel talks to the keymanager | |
32 | ||
5c0bb261 SN |
33 | Userland access to the offload is typically through a system such as |
34 | libreswan or KAME/raccoon, but the iproute2 'ip xfrm' command set can | |
35 | be handy when experimenting. An example command might look something | |
2b7c72e0 | 36 | like this for crypto offload: |
5c0bb261 SN |
37 | |
38 | ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ | |
39 | reqid 0x07 replay-window 32 \ | |
40 | aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ | |
41 | sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ | |
42 | offload dev eth4 dir in | |
43 | ||
2b7c72e0 LR |
44 | and for packet offload |
45 | ||
46 | ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ | |
47 | reqid 0x07 replay-window 32 \ | |
48 | aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ | |
49 | sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ | |
50 | offload packet dev eth4 dir in | |
51 | ||
52 | ip x p add src 14.0.0.70 dst 14.0.0.52 offload packet dev eth4 dir in | |
53 | tmpl src 14.0.0.70 dst 14.0.0.52 proto esp reqid 10000 mode transport | |
54 | ||
5c0bb261 SN |
55 | Yes, that's ugly, but that's what shell scripts and/or libreswan are for. |
56 | ||
57 | ||
58 | ||
59 | Callbacks to implement | |
60 | ====================== | |
61 | ||
c4a0eb93 MCC |
62 | :: |
63 | ||
64 | /* from include/linux/netdevice.h */ | |
65 | struct xfrmdev_ops { | |
2b7c72e0 | 66 | /* Crypto and Packet offload callbacks */ |
7681a4f5 | 67 | int (*xdo_dev_state_add) (struct xfrm_state *x, struct netlink_ext_ack *extack); |
5c0bb261 SN |
68 | void (*xdo_dev_state_delete) (struct xfrm_state *x); |
69 | void (*xdo_dev_state_free) (struct xfrm_state *x); | |
70 | bool (*xdo_dev_offload_ok) (struct sk_buff *skb, | |
71 | struct xfrm_state *x); | |
50bd870a | 72 | void (*xdo_dev_state_advance_esn) (struct xfrm_state *x); |
2b7c72e0 LR |
73 | |
74 | /* Solely packet offload callbacks */ | |
75 | void (*xdo_dev_state_update_curlft) (struct xfrm_state *x); | |
3089386d | 76 | int (*xdo_dev_policy_add) (struct xfrm_policy *x, struct netlink_ext_ack *extack); |
2b7c72e0 LR |
77 | void (*xdo_dev_policy_delete) (struct xfrm_policy *x); |
78 | void (*xdo_dev_policy_free) (struct xfrm_policy *x); | |
c4a0eb93 | 79 | }; |
5c0bb261 | 80 | |
2b7c72e0 LR |
81 | The NIC driver offering ipsec offload will need to implement callbacks |
82 | relevant to supported offload to make the offload available to the network | |
83 | stack's XFRM subsystem. Additionally, the feature bits NETIF_F_HW_ESP and | |
5c0bb261 SN |
84 | NETIF_F_HW_ESP_TX_CSUM will signal the availability of the offload. |
85 | ||
86 | ||
87 | ||
88 | Flow | |
89 | ==== | |
90 | ||
91 | At probe time and before the call to register_netdev(), the driver should | |
92 | set up local data structures and XFRM callbacks, and set the feature bits. | |
93 | The XFRM code's listener will finish the setup on NETDEV_REGISTER. | |
94 | ||
c4a0eb93 MCC |
95 | :: |
96 | ||
5c0bb261 SN |
97 | adapter->netdev->xfrmdev_ops = &ixgbe_xfrmdev_ops; |
98 | adapter->netdev->features |= NETIF_F_HW_ESP; | |
99 | adapter->netdev->hw_enc_features |= NETIF_F_HW_ESP; | |
100 | ||
101 | When new SAs are set up with a request for "offload" feature, the | |
102 | driver's xdo_dev_state_add() will be given the new SA to be offloaded | |
103 | and an indication of whether it is for Rx or Tx. The driver should | |
c4a0eb93 | 104 | |
5c0bb261 SN |
105 | - verify the algorithm is supported for offloads |
106 | - store the SA information (key, salt, target-ip, protocol, etc) | |
107 | - enable the HW offload of the SA | |
4a132095 | 108 | - return status value: |
c4a0eb93 MCC |
109 | |
110 | =========== =================================== | |
4a132095 | 111 | 0 success |
2b7c72e0 LR |
112 | -EOPNETSUPP offload not supported, try SW IPsec, |
113 | not applicable for packet offload mode | |
4a132095 | 114 | other fail the request |
c4a0eb93 | 115 | =========== =================================== |
5c0bb261 SN |
116 | |
117 | The driver can also set an offload_handle in the SA, an opaque void pointer | |
c4a0eb93 | 118 | that can be used to convey context into the fast-path offload requests:: |
5c0bb261 SN |
119 | |
120 | xs->xso.offload_handle = context; | |
121 | ||
122 | ||
123 | When the network stack is preparing an IPsec packet for an SA that has | |
124 | been setup for offload, it first calls into xdo_dev_offload_ok() with | |
125 | the skb and the intended offload state to ask the driver if the offload | |
126 | will serviceable. This can check the packet information to be sure the | |
127 | offload can be supported (e.g. IPv4 or IPv6, no IPv4 options, etc) and | |
128 | return true of false to signify its support. | |
129 | ||
2b7c72e0 | 130 | Crypto offload mode: |
5c0bb261 SN |
131 | When ready to send, the driver needs to inspect the Tx packet for the |
132 | offload information, including the opaque context, and set up the packet | |
c4a0eb93 | 133 | send accordingly:: |
5c0bb261 SN |
134 | |
135 | xs = xfrm_input_state(skb); | |
136 | context = xs->xso.offload_handle; | |
137 | set up HW for send | |
138 | ||
139 | The stack has already inserted the appropriate IPsec headers in the | |
140 | packet data, the offload just needs to do the encryption and fix up the | |
141 | header values. | |
142 | ||
143 | ||
144 | When a packet is received and the HW has indicated that it offloaded a | |
145 | decryption, the driver needs to add a reference to the decoded SA into | |
146 | the packet's skb. At this point the data should be decrypted but the | |
147 | IPsec headers are still in the packet data; they are removed later up | |
148 | the stack in xfrm_input(). | |
149 | ||
c4a0eb93 MCC |
150 | find and hold the SA that was used to the Rx skb:: |
151 | ||
5c0bb261 SN |
152 | get spi, protocol, and destination IP from packet headers |
153 | xs = find xs from (spi, protocol, dest_IP) | |
154 | xfrm_state_hold(xs); | |
155 | ||
c4a0eb93 MCC |
156 | store the state information into the skb:: |
157 | ||
4165079b FW |
158 | sp = secpath_set(skb); |
159 | if (!sp) return; | |
160 | sp->xvec[sp->len++] = xs; | |
161 | sp->olen++; | |
5c0bb261 | 162 | |
c4a0eb93 MCC |
163 | indicate the success and/or error status of the offload:: |
164 | ||
5c0bb261 SN |
165 | xo = xfrm_offload(skb); |
166 | xo->flags = CRYPTO_DONE; | |
167 | xo->status = crypto_status; | |
168 | ||
169 | hand the packet to napi_gro_receive() as usual | |
170 | ||
50bd870a YE |
171 | In ESN mode, xdo_dev_state_advance_esn() is called from xfrm_replay_advance_esn(). |
172 | Driver will check packet seq number and update HW ESN state machine if needed. | |
5c0bb261 | 173 | |
2b7c72e0 LR |
174 | Packet offload mode: |
175 | HW adds and deletes XFRM headers. So in RX path, XFRM stack is bypassed if HW | |
176 | reported success. In TX path, the packet lefts kernel without extra header | |
177 | and not encrypted, the HW is responsible to perform it. | |
178 | ||
5c0bb261 | 179 | When the SA is removed by the user, the driver's xdo_dev_state_delete() |
2b7c72e0 LR |
180 | and xdo_dev_policy_delete() are asked to disable the offload. Later, |
181 | xdo_dev_state_free() and xdo_dev_policy_free() are called from a garbage | |
182 | collection routine after all reference counts to the state and policy | |
5c0bb261 SN |
183 | have been removed and any remaining resources can be cleared for the |
184 | offload state. How these are used by the driver will depend on specific | |
185 | hardware needs. | |
186 | ||
187 | As a netdev is set to DOWN the XFRM stack's netdev listener will call | |
2b7c72e0 LR |
188 | xdo_dev_state_delete(), xdo_dev_policy_delete(), xdo_dev_state_free() and |
189 | xdo_dev_policy_free() on any remaining offloaded states. | |
190 | ||
191 | Outcome of HW handling packets, the XFRM core can't count hard, soft limits. | |
192 | The HW/driver are responsible to perform it and provide accurate data when | |
193 | xdo_dev_state_update_curlft() is called. In case of one of these limits | |
194 | occuried, the driver needs to call to xfrm_state_check_expire() to make sure | |
195 | that XFRM performs rekeying sequence. |