[openvswitch] / datapath / checksum.c

/*
 * Copyright (c) 2010, 2011 Nicira Networks.
 * Distributed under the terms of the GNU GPL version 2.
 *
 * Significant portions of this file may be copied from parts of the Linux
 * kernel, by Linus Torvalds and others.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/in.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/udp.h>

#include "checksum.h"
#include "datapath.h"

#ifdef NEED_CSUM_NORMALIZE

#if defined(CONFIG_XEN) && defined(HAVE_PROTO_DATA_VALID)
/* This code is based on skb_checksum_setup() from Xen's net/dev/core.c.  We
 * can't call this function directly because it isn't exported in all
 * versions. */
static int vswitch_skb_checksum_setup(struct sk_buff *skb)
{
        struct iphdr *iph;
        unsigned char *th;
        int err = -EPROTO;
        __u16 csum_start, csum_offset;

        if (!skb->proto_csum_blank)
                return 0;

        if (skb->protocol != htons(ETH_P_IP))
                goto out;

        if (!pskb_may_pull(skb, skb_network_header(skb) + sizeof(struct iphdr) - skb->data))
                goto out;

        iph = ip_hdr(skb);
        th = skb_network_header(skb) + 4 * iph->ihl;

        csum_start = th - skb->head;
        switch (iph->protocol) {
        case IPPROTO_TCP:
                csum_offset = offsetof(struct tcphdr, check);
                break;
        case IPPROTO_UDP:
                csum_offset = offsetof(struct udphdr, check);
                break;
        default:
                if (net_ratelimit())
                        pr_err("Attempting to checksum a non-TCP/UDP packet, "
                               "dropping a protocol %d packet",
                               iph->protocol);
                goto out;
        }

        if (!pskb_may_pull(skb, th + csum_offset + 2 - skb->data))
                goto out;

        skb->proto_csum_blank = 0;
        set_ip_summed(skb, OVS_CSUM_PARTIAL);
        set_skb_csum_pointers(skb, csum_start, csum_offset);

        err = 0;

out:
        return err;
}
#else
static int vswitch_skb_checksum_setup(struct sk_buff *skb)
{
        return 0;
}
#endif /* not Xen old style checksums */

/*
 *      compute_ip_summed - map external checksum state onto OVS representation
 *
 * @skb: Packet to manipulate.
 * @xmit: Whether we were on transmit path of network stack.  For example,
 *        this is true for the internal dev vport because it receives skbs
 *        that passed through dev_queue_xmit() but false for the netdev vport
 *        because its packets come from netif_receive_skb().
 *
 * Older kernels (and various versions of Xen) were not explicit enough about
 * checksum offload parameters and rely on a combination of context and
 * non standard fields.  This deals with all those variations so that we
 * can internally manipulate checksum offloads without worrying about kernel
 * version.
 *
 * Types of checksums that we can receive (these all refer to L4 checksums):
 * 1. CHECKSUM_NONE: Device that did not compute checksum, contains full
 *      (though not verified) checksum in packet but not in skb->csum.  Packets
 *      from the bridge local port will also have this type.
 * 2. CHECKSUM_COMPLETE (CHECKSUM_HW): Good device that computes checksums,
 *      also the GRE module.  This is the same as CHECKSUM_NONE, except it has
 *      a valid skb->csum.  Importantly, both contain a full checksum (not
 *      verified) in the packet itself.  The only difference is that if the
 *      packet gets to L4 processing on this machine (not in DomU) we won't
 *      have to recompute the checksum to verify.  Most hardware devices do not
 *      produce packets with this type, even if they support receive checksum
 *      offloading (they produce type #5).
 * 3. CHECKSUM_PARTIAL (CHECKSUM_HW): Packet without full checksum and needs to
 *      be computed if it is sent off box.  Unfortunately on earlier kernels,
 *      this case is impossible to distinguish from #2, despite having opposite
 *      meanings.  Xen adds an extra field on earlier kernels (see #4) in order
 *      to distinguish the different states.
 * 4. CHECKSUM_UNNECESSARY (with proto_csum_blank true): This packet was
 *      generated locally by a Xen DomU and has a partial checksum.  If it is
 *      handled on this machine (Dom0 or DomU), then the checksum will not be
 *      computed.  If it goes off box, the checksum in the packet needs to be
 *      completed.  Calling skb_checksum_setup converts this to CHECKSUM_HW
 *      (CHECKSUM_PARTIAL) so that the checksum can be completed.  In later
 *      kernels, this combination is replaced with CHECKSUM_PARTIAL.
 * 5. CHECKSUM_UNNECESSARY (with proto_csum_blank false): Packet with a correct
 *      full checksum or using a protocol without a checksum.  skb->csum is
 *      undefined.  This is common from devices with receive checksum
 *      offloading.  This is somewhat similar to CHECKSUM_NONE, except that
 *      nobody will try to verify the checksum with CHECKSUM_UNNECESSARY.
 *
 * Note that on earlier kernels, CHECKSUM_COMPLETE and CHECKSUM_PARTIAL are
 * both defined as CHECKSUM_HW.  Normally the meaning of CHECKSUM_HW is clear
 * based on whether it is on the transmit or receive path.  After the datapath
 * it will be intepreted as CHECKSUM_PARTIAL.  If the packet already has a
 * checksum, we will panic.  Since we can receive packets with checksums, we
 * assume that all CHECKSUM_HW packets have checksums and map them to
 * CHECKSUM_NONE, which has a similar meaning (the it is only different if the
 * packet is processed by the local IP stack, in which case it will need to
 * be reverified).  If we receive a packet with CHECKSUM_HW that really means
 * CHECKSUM_PARTIAL, it will be sent with the wrong checksum.  However, there
 * shouldn't be any devices that do this with bridging.
 */
int compute_ip_summed(struct sk_buff *skb, bool xmit)
{
        /* For our convenience these defines change repeatedly between kernel
         * versions, so we can't just copy them over...
         */
        switch (skb->ip_summed) {
        case CHECKSUM_NONE:
                set_ip_summed(skb, OVS_CSUM_NONE);
                break;
        case CHECKSUM_UNNECESSARY:
                set_ip_summed(skb, OVS_CSUM_UNNECESSARY);
                break;
#ifdef CHECKSUM_HW
        /* In theory this could be either CHECKSUM_PARTIAL or CHECKSUM_COMPLETE.
         * However, on the receive side we should only get CHECKSUM_PARTIAL
         * packets from Xen, which uses some special fields to represent this
         * (see vswitch_skb_checksum_setup()).  Since we can only make one type
         * work, pick the one that actually happens in practice.
         *
         * On the transmit side (basically after skb_checksum_setup()
         * has been run or on internal dev transmit), packets with
         * CHECKSUM_COMPLETE aren't generated, so assume CHECKSUM_PARTIAL.
         */
        case CHECKSUM_HW:
                if (!xmit)
                        set_ip_summed(skb, OVS_CSUM_COMPLETE);
                else
                        set_ip_summed(skb, OVS_CSUM_PARTIAL);
                break;
#else
        case CHECKSUM_COMPLETE:
                set_ip_summed(skb, OVS_CSUM_COMPLETE);
                break;
        case CHECKSUM_PARTIAL:
                set_ip_summed(skb, OVS_CSUM_PARTIAL);
                break;
#endif
        }

        OVS_CB(skb)->csum_start = skb_headroom(skb) + skb_transport_offset(skb);

        return vswitch_skb_checksum_setup(skb);
}

/*
 *     forward_ip_summed - map internal checksum state back onto native
 *                         kernel fields.
 *
 * @skb: Packet to manipulate.
 * @xmit: Whether we are about send on the transmit path the network stack.
 *        This follows the same logic as the @xmit field in compute_ip_summed().
 *        Generally, a given vport will have opposite values for @xmit passed to
 *        these two functions.
 *
 * When a packet is about to egress from OVS take our internal fields (including
 * any modifications we have made) and recreate the correct representation for
 * this kernel.  This may do things like change the transport header offset.
 */
void forward_ip_summed(struct sk_buff *skb, bool xmit)
{
        switch (get_ip_summed(skb)) {
        case OVS_CSUM_NONE:
                skb->ip_summed = CHECKSUM_NONE;
                break;
        case OVS_CSUM_UNNECESSARY:
                skb->ip_summed = CHECKSUM_UNNECESSARY;
#if defined(CONFIG_XEN) && defined(HAVE_PROTO_DATA_VALID)
                skb->proto_data_valid = 1;
#endif
                break;
#ifdef CHECKSUM_HW
        case OVS_CSUM_COMPLETE:
                if (!xmit)
                        skb->ip_summed = CHECKSUM_HW;
                else
                        skb->ip_summed = CHECKSUM_NONE;
                break;
        case OVS_CSUM_PARTIAL:
                if (!xmit) {
                        skb->ip_summed = CHECKSUM_UNNECESSARY;
#if defined(CONFIG_XEN) && defined(HAVE_PROTO_DATA_VALID)
                        skb->proto_csum_blank = 1;
#endif
                } else {
                        skb->ip_summed = CHECKSUM_HW;
                }
                break;
#else
        case OVS_CSUM_COMPLETE:
                skb->ip_summed = CHECKSUM_COMPLETE;
                break;
        case OVS_CSUM_PARTIAL:
                skb->ip_summed = CHECKSUM_PARTIAL;
                break;
#endif
        }

        if (get_ip_summed(skb) == OVS_CSUM_PARTIAL)
                skb_set_transport_header(skb, OVS_CB(skb)->csum_start -
                                              skb_headroom(skb));
}

u8 get_ip_summed(struct sk_buff *skb)
{
        return OVS_CB(skb)->ip_summed;
}

void set_ip_summed(struct sk_buff *skb, u8 ip_summed)
{
        OVS_CB(skb)->ip_summed = ip_summed;
}

void get_skb_csum_pointers(const struct sk_buff *skb, u16 *csum_start,
                           u16 *csum_offset)
{
        *csum_start = OVS_CB(skb)->csum_start;
        *csum_offset = skb->csum;
}

void set_skb_csum_pointers(struct sk_buff *skb, u16 csum_start,
                           u16 csum_offset)
{
        OVS_CB(skb)->csum_start = csum_start;
        skb->csum = csum_offset;
}
#endif /* NEED_CSUM_NORMALIZE */