[thirdparty/kernel/stable.git] / Documentation / networking / xfrm_device.txt


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