Re: [Qemu-devel] [PATCH 2/2] net/vmxnet3: Fix RX TCP/UDP checksum on partially summed packets

[Dmitry Fleytman]

> On Jul 14, 2015, at 11:55, Shmulik Ladkani <address@hidden> wrote:
> 
> From: Dana Rubin <address@hidden>
> 
> Convert partially summed packets to be fully checksummed.
> 
> In case csum offloaded packet, vmxnet3 implementation always passes an
> RxCompDesc with the "Checksum calculated and found correct" notification
> to the OS. This emulates the observed ESXi behavior.
> 
> Therefore, if packet has the NEEDS_CSUM bit set, we must calculate and
> place a fully computed checksum into the tcp/udp header. Otherwise, the
> OS driver will receive a checksum-correct indication but with the actual
> tcp/udp checksum field having just the pseudo header csum value.
> 
> If host OS performs forwarding, it will forward an incorrectly
> checksummed packet.

Ack.

> 
> Signed-off-by: Dana Rubin <address@hidden>
> Signed-off-by: Shmulik Ladkani <address@hidden>
> ---
> hw/net/vmxnet3.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 58 insertions(+)
> 
> diff --git a/hw/net/vmxnet3.c b/hw/net/vmxnet3.c
> index dd22a0a..59b06b8 100644
> --- a/hw/net/vmxnet3.c
> +++ b/hw/net/vmxnet3.c
> @@ -885,6 +885,63 @@ vmxnet3_get_next_rx_descr(VMXNET3State *s, bool is_head,
>     }
> }
> 
> +/* In case packet was csum offloaded (either NEEDS_CSUM or DATA_VALID),
> + * the implementation always passes an RxCompDesc with a "Checksum
> + * calculated and found correct" to the OS (cnc=0 and tuc=1, see
> + * vmxnet3_rx_update_descr). This emulates the observed ESXi behavior.
> + *
> + * Therefore, if packet has the NEEDS_CSUM set, we must calculate
> + * and place a fully computed checksum into the tcp/udp header.
> + * Otherwise, the OS driver will receive a checksum-correct indication
> + * (CHECKSUM_UNNECESSARY), but with the actual tcp/udp checksum field
> + * having just the pseudo header csum value.
> + *
> + * While this is not a problem if packet is destined for local delivery,
> + * in the case the host OS performs forwarding, it will forward an
> + * incorrectly checksummed packet.
> + */
> +static void vmxnet3_rx_need_csum_calculate(struct VmxnetRxPkt *pkt,
> +                                           const void *pkt_data,
> +                                           size_t pkt_len)
> +{
> +    struct virtio_net_hdr *vhdr;
> +    bool isip4, isip6, istcp, isudp;
> +    uint8_t *data;
> +    int len;
> +
> +    if (!vmxnet_rx_pkt_has_virt_hdr(pkt)) {
> +        return;
> +    }
> +
> +    vhdr = vmxnet_rx_pkt_get_vhdr(pkt);
> +    if (!VMXNET_FLAG_IS_SET(vhdr->flags, VIRTIO_NET_HDR_F_NEEDS_CSUM)) {
> +        return;
> +    }
> +
> +    vmxnet_rx_pkt_get_protocols(pkt, &isip4, &isip6, &isudp, &istcp);
> +    if (!(isip4 || isip6) || !(istcp || isudp)) {
> +        return;
> +    }
> +
> +    vmxnet3_dump_virt_hdr(vhdr);
> +
> +    /* Validate packet len: csum_start + scum_offset + length of csum field 
> */
> +    if (pkt_len < (vhdr->csum_start + vhdr->csum_offset + 2)) {
> +        VMW_PKPRN("packet len:%d < csum_start(%d) + csum_offset(%d) + 2, "
> +                  "cannot calculate checksum",
> +                  len, vhdr->csum_start, vhdr->csum_offset);
> +        return;
> +    }
> +
> +    data = (uint8_t *)pkt_data + vhdr->csum_start;
> +    len = pkt_len - vhdr->csum_start;
> +    /* Put the checksum obtained into the packet */
> +    stw_be_p(data + vhdr->csum_offset, net_raw_checksum(data, len));
> +
> +    vhdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
> +    vhdr->flags |= VIRTIO_NET_HDR_F_DATA_VALID;
> +}
> +
> static void vmxnet3_rx_update_descr(struct VmxnetRxPkt *pkt,
>     struct Vmxnet3_RxCompDesc *rxcd)
> {
> @@ -1898,6 +1955,7 @@ vmxnet3_receive(NetClientState *nc, const uint8_t *buf, 
> size_t size)
> 
>     if (vmxnet3_rx_filter_may_indicate(s, buf, size)) {
>         vmxnet_rx_pkt_set_protocols(s->rx_pkt, buf, size);
> +        vmxnet3_rx_need_csum_calculate(s->rx_pkt, buf, size);
>         vmxnet_rx_pkt_attach_data(s->rx_pkt, buf, size, s->rx_vlan_stripping);
>         bytes_indicated = vmxnet3_indicate_packet(s) ? size : -1;
>         if (bytes_indicated < size) {
> -- 
> 1.9.1
>