Commit | Line | Data |
---|---|---|
c4a0eb93 | 1 | .. SPDX-License-Identifier: GPL-2.0 |
5c0bb261 SN |
2 | |
3 | =============================================== | |
4 | XFRM device - offloading the IPsec computations | |
5 | =============================================== | |
c4a0eb93 | 6 | |
5c0bb261 SN |
7 | Shannon Nelson <shannon.nelson@oracle.com> |
8 | ||
9 | ||
10 | Overview | |
11 | ======== | |
12 | ||
13 | IPsec is a useful feature for securing network traffic, but the | |
14 | computational cost is high: a 10Gbps link can easily be brought down | |
15 | to under 1Gbps, depending on the traffic and link configuration. | |
16 | Luckily, there are NICs that offer a hardware based IPsec offload which | |
17 | can radically increase throughput and decrease CPU utilization. The XFRM | |
18 | Device interface allows NIC drivers to offer to the stack access to the | |
19 | hardware offload. | |
20 | ||
21 | Userland access to the offload is typically through a system such as | |
22 | libreswan or KAME/raccoon, but the iproute2 'ip xfrm' command set can | |
23 | be handy when experimenting. An example command might look something | |
c4a0eb93 | 24 | like this:: |
5c0bb261 SN |
25 | |
26 | ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ | |
27 | reqid 0x07 replay-window 32 \ | |
28 | aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ | |
29 | sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ | |
30 | offload dev eth4 dir in | |
31 | ||
32 | Yes, that's ugly, but that's what shell scripts and/or libreswan are for. | |
33 | ||
34 | ||
35 | ||
36 | Callbacks to implement | |
37 | ====================== | |
38 | ||
c4a0eb93 MCC |
39 | :: |
40 | ||
41 | /* from include/linux/netdevice.h */ | |
42 | struct xfrmdev_ops { | |
5c0bb261 SN |
43 | int (*xdo_dev_state_add) (struct xfrm_state *x); |
44 | void (*xdo_dev_state_delete) (struct xfrm_state *x); | |
45 | void (*xdo_dev_state_free) (struct xfrm_state *x); | |
46 | bool (*xdo_dev_offload_ok) (struct sk_buff *skb, | |
47 | struct xfrm_state *x); | |
50bd870a | 48 | void (*xdo_dev_state_advance_esn) (struct xfrm_state *x); |
c4a0eb93 | 49 | }; |
5c0bb261 SN |
50 | |
51 | The NIC driver offering ipsec offload will need to implement these | |
52 | callbacks to make the offload available to the network stack's | |
53 | XFRM subsytem. Additionally, the feature bits NETIF_F_HW_ESP and | |
54 | NETIF_F_HW_ESP_TX_CSUM will signal the availability of the offload. | |
55 | ||
56 | ||
57 | ||
58 | Flow | |
59 | ==== | |
60 | ||
61 | At probe time and before the call to register_netdev(), the driver should | |
62 | set up local data structures and XFRM callbacks, and set the feature bits. | |
63 | The XFRM code's listener will finish the setup on NETDEV_REGISTER. | |
64 | ||
c4a0eb93 MCC |
65 | :: |
66 | ||
5c0bb261 SN |
67 | adapter->netdev->xfrmdev_ops = &ixgbe_xfrmdev_ops; |
68 | adapter->netdev->features |= NETIF_F_HW_ESP; | |
69 | adapter->netdev->hw_enc_features |= NETIF_F_HW_ESP; | |
70 | ||
71 | When new SAs are set up with a request for "offload" feature, the | |
72 | driver's xdo_dev_state_add() will be given the new SA to be offloaded | |
73 | and an indication of whether it is for Rx or Tx. The driver should | |
c4a0eb93 | 74 | |
5c0bb261 SN |
75 | - verify the algorithm is supported for offloads |
76 | - store the SA information (key, salt, target-ip, protocol, etc) | |
77 | - enable the HW offload of the SA | |
4a132095 | 78 | - return status value: |
c4a0eb93 MCC |
79 | |
80 | =========== =================================== | |
4a132095 SN |
81 | 0 success |
82 | -EOPNETSUPP offload not supported, try SW IPsec | |
83 | other fail the request | |
c4a0eb93 | 84 | =========== =================================== |
5c0bb261 SN |
85 | |
86 | The driver can also set an offload_handle in the SA, an opaque void pointer | |
c4a0eb93 | 87 | that can be used to convey context into the fast-path offload requests:: |
5c0bb261 SN |
88 | |
89 | xs->xso.offload_handle = context; | |
90 | ||
91 | ||
92 | When the network stack is preparing an IPsec packet for an SA that has | |
93 | been setup for offload, it first calls into xdo_dev_offload_ok() with | |
94 | the skb and the intended offload state to ask the driver if the offload | |
95 | will serviceable. This can check the packet information to be sure the | |
96 | offload can be supported (e.g. IPv4 or IPv6, no IPv4 options, etc) and | |
97 | return true of false to signify its support. | |
98 | ||
99 | When ready to send, the driver needs to inspect the Tx packet for the | |
100 | offload information, including the opaque context, and set up the packet | |
c4a0eb93 | 101 | send accordingly:: |
5c0bb261 SN |
102 | |
103 | xs = xfrm_input_state(skb); | |
104 | context = xs->xso.offload_handle; | |
105 | set up HW for send | |
106 | ||
107 | The stack has already inserted the appropriate IPsec headers in the | |
108 | packet data, the offload just needs to do the encryption and fix up the | |
109 | header values. | |
110 | ||
111 | ||
112 | When a packet is received and the HW has indicated that it offloaded a | |
113 | decryption, the driver needs to add a reference to the decoded SA into | |
114 | the packet's skb. At this point the data should be decrypted but the | |
115 | IPsec headers are still in the packet data; they are removed later up | |
116 | the stack in xfrm_input(). | |
117 | ||
c4a0eb93 MCC |
118 | find and hold the SA that was used to the Rx skb:: |
119 | ||
5c0bb261 SN |
120 | get spi, protocol, and destination IP from packet headers |
121 | xs = find xs from (spi, protocol, dest_IP) | |
122 | xfrm_state_hold(xs); | |
123 | ||
c4a0eb93 MCC |
124 | store the state information into the skb:: |
125 | ||
4165079b FW |
126 | sp = secpath_set(skb); |
127 | if (!sp) return; | |
128 | sp->xvec[sp->len++] = xs; | |
129 | sp->olen++; | |
5c0bb261 | 130 | |
c4a0eb93 MCC |
131 | indicate the success and/or error status of the offload:: |
132 | ||
5c0bb261 SN |
133 | xo = xfrm_offload(skb); |
134 | xo->flags = CRYPTO_DONE; | |
135 | xo->status = crypto_status; | |
136 | ||
137 | hand the packet to napi_gro_receive() as usual | |
138 | ||
50bd870a YE |
139 | In ESN mode, xdo_dev_state_advance_esn() is called from xfrm_replay_advance_esn(). |
140 | Driver will check packet seq number and update HW ESN state machine if needed. | |
5c0bb261 SN |
141 | |
142 | When the SA is removed by the user, the driver's xdo_dev_state_delete() | |
143 | is asked to disable the offload. Later, xdo_dev_state_free() is called | |
144 | from a garbage collection routine after all reference counts to the state | |
145 | have been removed and any remaining resources can be cleared for the | |
146 | offload state. How these are used by the driver will depend on specific | |
147 | hardware needs. | |
148 | ||
149 | As a netdev is set to DOWN the XFRM stack's netdev listener will call | |
150 | xdo_dev_state_delete() and xdo_dev_state_free() on any remaining offloaded | |
151 | states. |