1.. SPDX-License-Identifier: GPL-2.0 2.. _xfrm_device: 3 4=============================================== 5XFRM device - offloading the IPsec computations 6=============================================== 7 8Shannon Nelson <shannon.nelson@oracle.com> 9Leon Romanovsky <leonro@nvidia.com> 10 11 12Overview 13======== 14 15IPsec is a useful feature for securing network traffic, but the 16computational cost is high: a 10Gbps link can easily be brought down 17to under 1Gbps, depending on the traffic and link configuration. 18Luckily, there are NICs that offer a hardware based IPsec offload which 19can radically increase throughput and decrease CPU utilization. The XFRM 20Device interface allows NIC drivers to offer to the stack access to the 21hardware offload. 22 23Right now, there are two types of hardware offload that kernel supports. 24 * IPsec crypto offload: 25 * NIC performs encrypt/decrypt 26 * Kernel does everything else 27 * IPsec packet offload: 28 * NIC performs encrypt/decrypt 29 * NIC does encapsulation 30 * Kernel and NIC have SA and policy in-sync 31 * NIC handles the SA and policies states 32 * The Kernel talks to the keymanager 33 34Userland access to the offload is typically through a system such as 35libreswan or KAME/raccoon, but the iproute2 'ip xfrm' command set can 36be handy when experimenting. An example command might look something 37like this for crypto offload: 38 39 ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ 40 reqid 0x07 replay-window 32 \ 41 aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ 42 sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ 43 offload dev eth4 dir in 44 45and for packet offload 46 47 ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ 48 reqid 0x07 replay-window 32 \ 49 aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ 50 sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ 51 offload packet dev eth4 dir in 52 53 ip x p add src 14.0.0.70 dst 14.0.0.52 offload packet dev eth4 dir in 54 tmpl src 14.0.0.70 dst 14.0.0.52 proto esp reqid 10000 mode transport 55 56Yes, that's ugly, but that's what shell scripts and/or libreswan are for. 57 58 59 60Callbacks to implement 61====================== 62 63:: 64 65 /* from include/linux/netdevice.h */ 66 struct xfrmdev_ops { 67 /* Crypto and Packet offload callbacks */ 68 int (*xdo_dev_state_add) (struct xfrm_state *x, struct netlink_ext_ack *extack); 69 void (*xdo_dev_state_delete) (struct xfrm_state *x); 70 void (*xdo_dev_state_free) (struct xfrm_state *x); 71 bool (*xdo_dev_offload_ok) (struct sk_buff *skb, 72 struct xfrm_state *x); 73 void (*xdo_dev_state_advance_esn) (struct xfrm_state *x); 74 void (*xdo_dev_state_update_stats) (struct xfrm_state *x); 75 76 /* Solely packet offload callbacks */ 77 int (*xdo_dev_policy_add) (struct xfrm_policy *x, struct netlink_ext_ack *extack); 78 void (*xdo_dev_policy_delete) (struct xfrm_policy *x); 79 void (*xdo_dev_policy_free) (struct xfrm_policy *x); 80 }; 81 82The NIC driver offering ipsec offload will need to implement callbacks 83relevant to supported offload to make the offload available to the network 84stack's XFRM subsystem. Additionally, the feature bits NETIF_F_HW_ESP and 85NETIF_F_HW_ESP_TX_CSUM will signal the availability of the offload. 86 87 88 89Flow 90==== 91 92At probe time and before the call to register_netdev(), the driver should 93set up local data structures and XFRM callbacks, and set the feature bits. 94The XFRM code's listener will finish the setup on NETDEV_REGISTER. 95 96:: 97 98 adapter->netdev->xfrmdev_ops = &ixgbe_xfrmdev_ops; 99 adapter->netdev->features |= NETIF_F_HW_ESP; 100 adapter->netdev->hw_enc_features |= NETIF_F_HW_ESP; 101 102When new SAs are set up with a request for "offload" feature, the 103driver's xdo_dev_state_add() will be given the new SA to be offloaded 104and an indication of whether it is for Rx or Tx. The driver should 105 106 - verify the algorithm is supported for offloads 107 - store the SA information (key, salt, target-ip, protocol, etc) 108 - enable the HW offload of the SA 109 - return status value: 110 111 =========== =================================== 112 0 success 113 -EOPNETSUPP offload not supported, try SW IPsec, 114 not applicable for packet offload mode 115 other fail the request 116 =========== =================================== 117 118The driver can also set an offload_handle in the SA, an opaque void pointer 119that can be used to convey context into the fast-path offload requests:: 120 121 xs->xso.offload_handle = context; 122 123 124When the network stack is preparing an IPsec packet for an SA that has 125been setup for offload, it first calls into xdo_dev_offload_ok() with 126the skb and the intended offload state to ask the driver if the offload 127will serviceable. This can check the packet information to be sure the 128offload can be supported (e.g. IPv4 or IPv6, no IPv4 options, etc) and 129return true of false to signify its support. 130 131Crypto offload mode: 132When ready to send, the driver needs to inspect the Tx packet for the 133offload information, including the opaque context, and set up the packet 134send accordingly:: 135 136 xs = xfrm_input_state(skb); 137 context = xs->xso.offload_handle; 138 set up HW for send 139 140The stack has already inserted the appropriate IPsec headers in the 141packet data, the offload just needs to do the encryption and fix up the 142header values. 143 144 145When a packet is received and the HW has indicated that it offloaded a 146decryption, the driver needs to add a reference to the decoded SA into 147the packet's skb. At this point the data should be decrypted but the 148IPsec headers are still in the packet data; they are removed later up 149the stack in xfrm_input(). 150 151 find and hold the SA that was used to the Rx skb:: 152 153 get spi, protocol, and destination IP from packet headers 154 xs = find xs from (spi, protocol, dest_IP) 155 xfrm_state_hold(xs); 156 157 store the state information into the skb:: 158 159 sp = secpath_set(skb); 160 if (!sp) return; 161 sp->xvec[sp->len++] = xs; 162 sp->olen++; 163 164 indicate the success and/or error status of the offload:: 165 166 xo = xfrm_offload(skb); 167 xo->flags = CRYPTO_DONE; 168 xo->status = crypto_status; 169 170 hand the packet to napi_gro_receive() as usual 171 172In ESN mode, xdo_dev_state_advance_esn() is called from xfrm_replay_advance_esn(). 173Driver will check packet seq number and update HW ESN state machine if needed. 174 175Packet offload mode: 176HW adds and deletes XFRM headers. So in RX path, XFRM stack is bypassed if HW 177reported success. In TX path, the packet lefts kernel without extra header 178and not encrypted, the HW is responsible to perform it. 179 180When the SA is removed by the user, the driver's xdo_dev_state_delete() 181and xdo_dev_policy_delete() are asked to disable the offload. Later, 182xdo_dev_state_free() and xdo_dev_policy_free() are called from a garbage 183collection routine after all reference counts to the state and policy 184have been removed and any remaining resources can be cleared for the 185offload state. How these are used by the driver will depend on specific 186hardware needs. 187 188As a netdev is set to DOWN the XFRM stack's netdev listener will call 189xdo_dev_state_delete(), xdo_dev_policy_delete(), xdo_dev_state_free() and 190xdo_dev_policy_free() on any remaining offloaded states. 191 192Outcome of HW handling packets, the XFRM core can't count hard, soft limits. 193The HW/driver are responsible to perform it and provide accurate data when 194xdo_dev_state_update_stats() is called. In case of one of these limits 195occuried, the driver needs to call to xfrm_state_check_expire() to make sure 196that XFRM performs rekeying sequence. 197