mirror of https://gitee.com/openkylin/linux.git
152 lines
5.3 KiB
ReStructuredText
152 lines
5.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===============================================
|
|
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.
|