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Diffstat (limited to 'Documentation/networking/xfrm_device.txt')
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diff --git a/Documentation/networking/xfrm_device.txt b/Documentation/networking/xfrm_device.txt deleted file mode 100644 index a1c904dc70dc..000000000000 --- a/Documentation/networking/xfrm_device.txt +++ /dev/null @@ -1,140 +0,0 @@ - -=============================================== -XFRM device - offloading the IPsec computations -=============================================== -Shannon Nelson <shannon.nelson@oracle.com> - - -Overview -======== - -IPsec is a useful feature for securing network traffic, but the -computational cost is high: a 10Gbps link can easily be brought down -to under 1Gbps, depending on the traffic and link configuration. -Luckily, there are NICs that offer a hardware based IPsec offload which -can radically increase throughput and decrease CPU utilization. The XFRM -Device interface allows NIC drivers to offer to the stack access to the -hardware offload. - -Userland access to the offload is typically through a system such as -libreswan or KAME/raccoon, but the iproute2 'ip xfrm' command set can -be handy when experimenting. An example command might look something -like this: - - ip x s add proto esp dst 14.0.0.70 src 14.0.0.52 spi 0x07 mode transport \ - reqid 0x07 replay-window 32 \ - aead 'rfc4106(gcm(aes))' 0x44434241343332312423222114131211f4f3f2f1 128 \ - sel src 14.0.0.52/24 dst 14.0.0.70/24 proto tcp \ - offload dev eth4 dir in - -Yes, that's ugly, but that's what shell scripts and/or libreswan are for. - - - -Callbacks to implement -====================== - -/* from include/linux/netdevice.h */ -struct xfrmdev_ops { - int (*xdo_dev_state_add) (struct xfrm_state *x); - void (*xdo_dev_state_delete) (struct xfrm_state *x); - void (*xdo_dev_state_free) (struct xfrm_state *x); - bool (*xdo_dev_offload_ok) (struct sk_buff *skb, - struct xfrm_state *x); - void (*xdo_dev_state_advance_esn) (struct xfrm_state *x); -}; - -The NIC driver offering ipsec offload will need to implement these -callbacks to make the offload available to the network stack's -XFRM subsytem. Additionally, the feature bits NETIF_F_HW_ESP and -NETIF_F_HW_ESP_TX_CSUM will signal the availability of the offload. - - - -Flow -==== - -At probe time and before the call to register_netdev(), the driver should -set up local data structures and XFRM callbacks, and set the feature bits. -The XFRM code's listener will finish the setup on NETDEV_REGISTER. - - adapter->netdev->xfrmdev_ops = &ixgbe_xfrmdev_ops; - adapter->netdev->features |= NETIF_F_HW_ESP; - adapter->netdev->hw_enc_features |= NETIF_F_HW_ESP; - -When new SAs are set up with a request for "offload" feature, the -driver's xdo_dev_state_add() will be given the new SA to be offloaded -and an indication of whether it is for Rx or Tx. The driver should - - verify the algorithm is supported for offloads - - store the SA information (key, salt, target-ip, protocol, etc) - - enable the HW offload of the SA - - return status value: - 0 success - -EOPNETSUPP offload not supported, try SW IPsec - other fail the request - -The driver can also set an offload_handle in the SA, an opaque void pointer -that can be used to convey context into the fast-path offload requests. - - xs->xso.offload_handle = context; - - -When the network stack is preparing an IPsec packet for an SA that has -been setup for offload, it first calls into xdo_dev_offload_ok() with -the skb and the intended offload state to ask the driver if the offload -will serviceable. This can check the packet information to be sure the -offload can be supported (e.g. IPv4 or IPv6, no IPv4 options, etc) and -return true of false to signify its support. - -When ready to send, the driver needs to inspect the Tx packet for the -offload information, including the opaque context, and set up the packet -send accordingly. - - xs = xfrm_input_state(skb); - context = xs->xso.offload_handle; - set up HW for send - -The stack has already inserted the appropriate IPsec headers in the -packet data, the offload just needs to do the encryption and fix up the -header values. - - -When a packet is received and the HW has indicated that it offloaded a -decryption, the driver needs to add a reference to the decoded SA into -the packet's skb. At this point the data should be decrypted but the -IPsec headers are still in the packet data; they are removed later up -the stack in xfrm_input(). - - find and hold the SA that was used to the Rx skb - get spi, protocol, and destination IP from packet headers - xs = find xs from (spi, protocol, dest_IP) - xfrm_state_hold(xs); - - store the state information into the skb - sp = secpath_set(skb); - if (!sp) return; - sp->xvec[sp->len++] = xs; - sp->olen++; - - indicate the success and/or error status of the offload - xo = xfrm_offload(skb); - xo->flags = CRYPTO_DONE; - xo->status = crypto_status; - - hand the packet to napi_gro_receive() as usual - -In ESN mode, xdo_dev_state_advance_esn() is called from xfrm_replay_advance_esn(). -Driver will check packet seq number and update HW ESN state machine if needed. - -When the SA is removed by the user, the driver's xdo_dev_state_delete() -is asked to disable the offload. Later, xdo_dev_state_free() is called -from a garbage collection routine after all reference counts to the state -have been removed and any remaining resources can be cleared for the -offload state. How these are used by the driver will depend on specific -hardware needs. - -As a netdev is set to DOWN the XFRM stack's netdev listener will call -xdo_dev_state_delete() and xdo_dev_state_free() on any remaining offloaded -states. - - |