Date:   Thu, 10 May 2018 21:27:18 +0200
From:   Mathieu Xhonneux <m.xhonneux@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org, borkmann@...earbox.net, ast@...nel.org,
        David Miller <davem@...emloft.net>, shm@...ulusnetworks.com,
        roopa@...ulusnetworks.com, brouer@...hat.com, toke@...e.dk,
        john.fastabend@...il.com
Subject: Re: [bpf-next v3 8/9] bpf: Provide helper to do forwarding lookups in
 kernel FIB table

I'm quite interested in this helper to implement OAM features (through
other hooks, e.g. the BPF LWT hook). Do you have an idea about how it
behaves with ECMP routes (with IPv4 and/or IPv6) ? In IPv6, I'm
guessing that the returned gateway address is always a link-local
address ?

Thanks.

2018-05-10 5:34 GMT+02:00 David Ahern <dsahern@...il.com>:
>
> Provide a helper for doing a FIB and neighbor lookup in the kernel
> tables from an XDP program. The helper provides a fastpath for forwarding
> packets. If the packet is a local delivery or for any reason is not a
> simple lookup and forward, the packet continues up the stack.
>
> If it is to be forwarded, the forwarding can be done directly if the
> neighbor is already known. If the neighbor does not exist, the first
> few packets go up the stack for neighbor resolution. Once resolved, the
> xdp program provides the fast path.
>
> On successful lookup the nexthop dmac, current device smac and egress
> device index are returned.
>
> The API supports IPv4, IPv6 and MPLS protocols, but only IPv4 and IPv6
> are implemented in this patch. The API includes layer 4 parameters if
> the XDP program chooses to do deep packet inspection to allow compare
> against ACLs implemented as FIB rules.
>
> Header rewrite is left to the XDP program.
>
> The lookup takes 2 flags:
> - BPF_FIB_LOOKUP_DIRECT to do a lookup that bypasses FIB rules and goes
>   straight to the table associated with the device (expert setting for
>   those looking to maximize throughput)
>
> - BPF_FIB_LOOKUP_OUTPUT to do a lookup from the egress perspective.
>   Default is an ingress lookup.
>
> Initial performance numbers collected by Jesper, forwarded packets/sec:
>
>        Full stack    XDP FIB lookup    XDP Direct lookup
> IPv4   1,947,969       7,074,156          7,415,333
> IPv6   1,728,000       6,165,504          7,262,720
>
> These number are single CPU core forwarding on a Broadwell
> E5-1650 v4 @ 3.60GHz.
>
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  include/uapi/linux/bpf.h |  81 +++++++++++++-
>  net/core/filter.c        | 267 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 347 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d615c777b573..02e4112510f8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1828,6 +1828,33 @@ union bpf_attr {
>   *     Return
>   *             0 on success, or a negative error in case of failure.
>   *
> + *
> + * int bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen, u32 flags)
> + *     Description
> + *             Do FIB lookup in kernel tables using parameters in *params*.
> + *             If lookup is successful and result shows packet is to be
> + *             forwarded, the neighbor tables are searched for the nexthop.
> + *             If successful (ie., FIB lookup shows forwarding and nexthop
> + *             is resolved), the nexthop address is returned in ipv4_dst,
> + *             ipv6_dst or mpls_out based on family, smac is set to mac
> + *             address of egress device, dmac is set to nexthop mac address,
> + *             rt_metric is set to metric from route.
> + *
> + *             *plen* argument is the size of the passed in struct.
> + *             *flags* argument can be one or more BPF_FIB_LOOKUP_ flags:
> + *
> + *             **BPF_FIB_LOOKUP_DIRECT** means do a direct table lookup vs
> + *             full lookup using FIB rules
> + *             **BPF_FIB_LOOKUP_OUTPUT** means do lookup from an egress
> + *             perspective (default is ingress)
> + *
> + *             *ctx* is either **struct xdp_md** for XDP programs or
> + *             **struct sk_buff** tc cls_act programs.
> + *
> + *     Return
> + *             Egress device index on success, 0 if packet needs to continue
> + *             up the stack for further processing or a negative error in case
> + *             of failure.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -1898,7 +1925,8 @@ union bpf_attr {
>         FN(xdp_adjust_tail),            \
>         FN(skb_get_xfrm_state),         \
>         FN(get_stack),                  \
> -       FN(skb_load_bytes_relative),
> +       FN(skb_load_bytes_relative),    \
> +       FN(fib_lookup),
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> @@ -2321,4 +2349,55 @@ struct bpf_raw_tracepoint_args {
>         __u64 args[0];
>  };
>
> +/* DIRECT:  Skip the FIB rules and go to FIB table associated with device
> + * OUTPUT:  Do lookup from egress perspective; default is ingress
> + */
> +#define BPF_FIB_LOOKUP_DIRECT  BIT(0)
> +#define BPF_FIB_LOOKUP_OUTPUT  BIT(1)
> +
> +struct bpf_fib_lookup {
> +       /* input */
> +       __u8    family;   /* network family, AF_INET, AF_INET6, AF_MPLS */
> +
> +       /* set if lookup is to consider L4 data - e.g., FIB rules */
> +       __u8    l4_protocol;
> +       __be16  sport;
> +       __be16  dport;
> +
> +       /* total length of packet from network header - used for MTU check */
> +       __u16   tot_len;
> +       __u32   ifindex;  /* L3 device index for lookup */
> +
> +       union {
> +               /* inputs to lookup */
> +               __u8    tos;            /* AF_INET  */
> +               __be32  flowlabel;      /* AF_INET6 */
> +
> +               /* output: metric of fib result */
> +               __u32 rt_metric;
> +       };
> +
> +       union {
> +               __be32          mpls_in;
> +               __be32          ipv4_src;
> +               __u32           ipv6_src[4];  /* in6_addr; network order */
> +       };
> +
> +       /* input to bpf_fib_lookup, *dst is destination address.
> +        * output: bpf_fib_lookup sets to gateway address
> +        */
> +       union {
> +               /* return for MPLS lookups */
> +               __be32          mpls_out[4];  /* support up to 4 labels */
> +               __be32          ipv4_dst;
> +               __u32           ipv6_dst[4];  /* in6_addr; network order */
> +       };
> +
> +       /* output */
> +       __be16  h_vlan_proto;
> +       __be16  h_vlan_TCI;
> +       __u8    smac[6];     /* ETH_ALEN */
> +       __u8    dmac[6];     /* ETH_ALEN */
> +};
> +
>  #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 0baa715e4699..ca60d2872da4 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -60,6 +60,10 @@
>  #include <net/xfrm.h>
>  #include <linux/bpf_trace.h>
>  #include <net/xdp_sock.h>
> +#include <linux/inetdevice.h>
> +#include <net/ip_fib.h>
> +#include <net/flow.h>
> +#include <net/arp.h>
>
>  /**
>   *     sk_filter_trim_cap - run a packet through a socket filter
> @@ -4032,6 +4036,265 @@ static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {
>  };
>  #endif
>
> +#if IS_ENABLED(CONFIG_INET) || IS_ENABLED(CONFIG_IPV6)
> +static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params,
> +                                 const struct neighbour *neigh,
> +                                 const struct net_device *dev)
> +{
> +       memcpy(params->dmac, neigh->ha, ETH_ALEN);
> +       memcpy(params->smac, dev->dev_addr, ETH_ALEN);
> +       params->h_vlan_TCI = 0;
> +       params->h_vlan_proto = 0;
> +
> +       return dev->ifindex;
> +}
> +#endif
> +
> +#if IS_ENABLED(CONFIG_INET)
> +static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
> +                              u32 flags)
> +{
> +       struct in_device *in_dev;
> +       struct neighbour *neigh;
> +       struct net_device *dev;
> +       struct fib_result res;
> +       struct fib_nh *nh;
> +       struct flowi4 fl4;
> +       int err;
> +
> +       dev = dev_get_by_index_rcu(net, params->ifindex);
> +       if (unlikely(!dev))
> +               return -ENODEV;
> +
> +       /* verify forwarding is enabled on this interface */
> +       in_dev = __in_dev_get_rcu(dev);
> +       if (unlikely(!in_dev || !IN_DEV_FORWARD(in_dev)))
> +               return 0;
> +
> +       if (flags & BPF_FIB_LOOKUP_OUTPUT) {
> +               fl4.flowi4_iif = 1;
> +               fl4.flowi4_oif = params->ifindex;
> +       } else {
> +               fl4.flowi4_iif = params->ifindex;
> +               fl4.flowi4_oif = 0;
> +       }
> +       fl4.flowi4_tos = params->tos & IPTOS_RT_MASK;
> +       fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
> +       fl4.flowi4_flags = 0;
> +
> +       fl4.flowi4_proto = params->l4_protocol;
> +       fl4.daddr = params->ipv4_dst;
> +       fl4.saddr = params->ipv4_src;
> +       fl4.fl4_sport = params->sport;
> +       fl4.fl4_dport = params->dport;
> +
> +       if (flags & BPF_FIB_LOOKUP_DIRECT) {
> +               u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
> +               struct fib_table *tb;
> +
> +               tb = fib_get_table(net, tbid);
> +               if (unlikely(!tb))
> +                       return 0;
> +
> +               err = fib_table_lookup(tb, &fl4, &res, FIB_LOOKUP_NOREF);
> +       } else {
> +               fl4.flowi4_mark = 0;
> +               fl4.flowi4_secid = 0;
> +               fl4.flowi4_tun_key.tun_id = 0;
> +               fl4.flowi4_uid = sock_net_uid(net, NULL);
> +
> +               err = fib_lookup(net, &fl4, &res, FIB_LOOKUP_NOREF);
> +       }
> +
> +       if (err || res.type != RTN_UNICAST)
> +               return 0;
> +
> +       if (res.fi->fib_nhs > 1)
> +               fib_select_path(net, &res, &fl4, NULL);
> +
> +       nh = &res.fi->fib_nh[res.nh_sel];
> +
> +       /* do not handle lwt encaps right now */
> +       if (nh->nh_lwtstate)
> +               return 0;
> +
> +       dev = nh->nh_dev;
> +       if (unlikely(!dev))
> +               return 0;
> +
> +       if (nh->nh_gw)
> +               params->ipv4_dst = nh->nh_gw;
> +
> +       params->rt_metric = res.fi->fib_priority;
> +
> +       /* xdp and cls_bpf programs are run in RCU-bh so
> +        * rcu_read_lock_bh is not needed here
> +        */
> +       neigh = __ipv4_neigh_lookup_noref(dev, (__force u32)params->ipv4_dst);
> +       if (neigh)
> +               return bpf_fib_set_fwd_params(params, neigh, dev);
> +
> +       return 0;
> +}
> +#endif
> +
> +#if IS_ENABLED(CONFIG_IPV6)
> +static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
> +                              u32 flags)
> +{
> +       struct in6_addr *src = (struct in6_addr *) params->ipv6_src;
> +       struct in6_addr *dst = (struct in6_addr *) params->ipv6_dst;
> +       struct neighbour *neigh;
> +       struct net_device *dev;
> +       struct inet6_dev *idev;
> +       struct fib6_info *f6i;
> +       struct flowi6 fl6;
> +       int strict = 0;
> +       int oif;
> +
> +       /* link local addresses are never forwarded */
> +       if (rt6_need_strict(dst) || rt6_need_strict(src))
> +               return 0;
> +
> +       dev = dev_get_by_index_rcu(net, params->ifindex);
> +       if (unlikely(!dev))
> +               return -ENODEV;
> +
> +       idev = __in6_dev_get_safely(dev);
> +       if (unlikely(!idev || !net->ipv6.devconf_all->forwarding))
> +               return 0;
> +
> +       if (flags & BPF_FIB_LOOKUP_OUTPUT) {
> +               fl6.flowi6_iif = 1;
> +               oif = fl6.flowi6_oif = params->ifindex;
> +       } else {
> +               oif = fl6.flowi6_iif = params->ifindex;
> +               fl6.flowi6_oif = 0;
> +               strict = RT6_LOOKUP_F_HAS_SADDR;
> +       }
> +       fl6.flowlabel = params->flowlabel;
> +       fl6.flowi6_scope = 0;
> +       fl6.flowi6_flags = 0;
> +       fl6.mp_hash = 0;
> +
> +       fl6.flowi6_proto = params->l4_protocol;
> +       fl6.daddr = *dst;
> +       fl6.saddr = *src;
> +       fl6.fl6_sport = params->sport;
> +       fl6.fl6_dport = params->dport;
> +
> +       if (flags & BPF_FIB_LOOKUP_DIRECT) {
> +               u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
> +               struct fib6_table *tb;
> +
> +               tb = ipv6_stub->fib6_get_table(net, tbid);
> +               if (unlikely(!tb))
> +                       return 0;
> +
> +               f6i = ipv6_stub->fib6_table_lookup(net, tb, oif, &fl6, strict);
> +       } else {
> +               fl6.flowi6_mark = 0;
> +               fl6.flowi6_secid = 0;
> +               fl6.flowi6_tun_key.tun_id = 0;
> +               fl6.flowi6_uid = sock_net_uid(net, NULL);
> +
> +               f6i = ipv6_stub->fib6_lookup(net, oif, &fl6, strict);
> +       }
> +
> +       if (unlikely(IS_ERR_OR_NULL(f6i) || f6i == net->ipv6.fib6_null_entry))
> +               return 0;
> +
> +       if (unlikely(f6i->fib6_flags & RTF_REJECT ||
> +           f6i->fib6_type != RTN_UNICAST))
> +               return 0;
> +
> +       if (f6i->fib6_nsiblings && fl6.flowi6_oif == 0)
> +               f6i = ipv6_stub->fib6_multipath_select(net, f6i, &fl6,
> +                                                      fl6.flowi6_oif, NULL,
> +                                                      strict);
> +
> +       if (f6i->fib6_nh.nh_lwtstate)
> +               return 0;
> +
> +       if (f6i->fib6_flags & RTF_GATEWAY)
> +               *dst = f6i->fib6_nh.nh_gw;
> +
> +       dev = f6i->fib6_nh.nh_dev;
> +       params->rt_metric = f6i->fib6_metric;
> +
> +       /* xdp and cls_bpf programs are run in RCU-bh so rcu_read_lock_bh is
> +        * not needed here. Can not use __ipv6_neigh_lookup_noref here
> +        * because we need to get nd_tbl via the stub
> +        */
> +       neigh = ___neigh_lookup_noref(ipv6_stub->nd_tbl, neigh_key_eq128,
> +                                     ndisc_hashfn, dst, dev);
> +       if (neigh)
> +               return bpf_fib_set_fwd_params(params, neigh, dev);
> +
> +       return 0;
> +}
> +#endif
> +
> +BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
> +          struct bpf_fib_lookup *, params, int, plen, u32, flags)
> +{
> +       if (plen < sizeof(*params))
> +               return -EINVAL;
> +
> +       switch (params->family) {
> +#if IS_ENABLED(CONFIG_INET)
> +       case AF_INET:
> +               return bpf_ipv4_fib_lookup(dev_net(ctx->rxq->dev), params,
> +                                          flags);
> +#endif
> +#if IS_ENABLED(CONFIG_IPV6)
> +       case AF_INET6:
> +               return bpf_ipv6_fib_lookup(dev_net(ctx->rxq->dev), params,
> +                                          flags);
> +#endif
> +       }
> +       return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_xdp_fib_lookup_proto = {
> +       .func           = bpf_xdp_fib_lookup,
> +       .gpl_only       = true,
> +       .ret_type       = RET_INTEGER,
> +       .arg1_type      = ARG_PTR_TO_CTX,
> +       .arg2_type      = ARG_PTR_TO_MEM,
> +       .arg3_type      = ARG_CONST_SIZE,
> +       .arg4_type      = ARG_ANYTHING,
> +};
> +
> +BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
> +          struct bpf_fib_lookup *, params, int, plen, u32, flags)
> +{
> +       if (plen < sizeof(*params))
> +               return -EINVAL;
> +
> +       switch (params->family) {
> +#if IS_ENABLED(CONFIG_INET)
> +       case AF_INET:
> +               return bpf_ipv4_fib_lookup(dev_net(skb->dev), params, flags);
> +#endif
> +#if IS_ENABLED(CONFIG_IPV6)
> +       case AF_INET6:
> +               return bpf_ipv6_fib_lookup(dev_net(skb->dev), params, flags);
> +#endif
> +       }
> +       return -ENOTSUPP;
> +}
> +
> +static const struct bpf_func_proto bpf_skb_fib_lookup_proto = {
> +       .func           = bpf_skb_fib_lookup,
> +       .gpl_only       = true,
> +       .ret_type       = RET_INTEGER,
> +       .arg1_type      = ARG_PTR_TO_CTX,
> +       .arg2_type      = ARG_PTR_TO_MEM,
> +       .arg3_type      = ARG_CONST_SIZE,
> +       .arg4_type      = ARG_ANYTHING,
> +};
> +
>  static const struct bpf_func_proto *
>  bpf_base_func_proto(enum bpf_func_id func_id)
>  {
> @@ -4181,6 +4444,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>         case BPF_FUNC_skb_get_xfrm_state:
>                 return &bpf_skb_get_xfrm_state_proto;
>  #endif
> +       case BPF_FUNC_fib_lookup:
> +               return &bpf_skb_fib_lookup_proto;
>         default:
>                 return bpf_base_func_proto(func_id);
>         }
> @@ -4206,6 +4471,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_xdp_redirect_map_proto;
>         case BPF_FUNC_xdp_adjust_tail:
>                 return &bpf_xdp_adjust_tail_proto;
> +       case BPF_FUNC_fib_lookup:
> +               return &bpf_xdp_fib_lookup_proto;
>         default:
>                 return bpf_base_func_proto(func_id);
>         }
> --
> 2.11.0
>

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