From 43e74c0267a35d6f5127218054b2d80c7fe801f5 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Fri, 28 Jun 2019 11:12:34 +0200 Subject: [PATCH] bpf_xdp_redirect_map: Perform map lookup in eBPF helper MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The bpf_redirect_map() helper used by XDP programs doesn't return any indication of whether it can successfully redirect to the map index it was given. Instead, BPF programs have to track this themselves, leading to programs using duplicate maps to track which entries are populated in the devmap. This patch fixes this by moving the map lookup into the bpf_redirect_map() helper, which makes it possible to return failure to the eBPF program. The lower bits of the flags argument is used as the return code, which means that existing users who pass a '0' flag argument will get XDP_ABORTED. With this, a BPF program can check the return code from the helper call and react by, for instance, substituting a different redirect. This works for any type of map used for redirect. Signed-off-by: Toke Høiland-Jørgensen Acked-by: Jonathan Lemon Acked-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann --- include/linux/filter.h | 1 + include/trace/events/xdp.h | 5 ++--- include/uapi/linux/bpf.h | 7 +++++-- net/core/filter.c | 32 ++++++++++++++++++-------------- 4 files changed, 26 insertions(+), 19 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index 92bd192f7786..1fe53e78c7e3 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -580,6 +580,7 @@ struct bpf_skb_data_end { struct bpf_redirect_info { u32 flags; u32 tgt_index; + void *tgt_value; struct bpf_map *map; struct bpf_map *map_to_flush; u32 kern_flags; diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h index 81e708c4b513..68899fdc985b 100644 --- a/include/trace/events/xdp.h +++ b/include/trace/events/xdp.h @@ -175,9 +175,8 @@ struct _bpf_dtab_netdev { #endif /* __DEVMAP_OBJ_TYPE */ #define devmap_ifindex(fwd, map) \ - (!fwd ? 0 : \ - ((map->map_type == BPF_MAP_TYPE_DEVMAP) ? \ - ((struct _bpf_dtab_netdev *)fwd)->dev->ifindex : 0)) + ((map->map_type == BPF_MAP_TYPE_DEVMAP) ? \ + ((struct _bpf_dtab_netdev *)fwd)->dev->ifindex : 0) #define _trace_xdp_redirect_map(dev, xdp, fwd, map, idx) \ trace_xdp_redirect_map(dev, xdp, devmap_ifindex(fwd, map), \ diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index a396b516a2b2..cffea1826a1f 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1571,8 +1571,11 @@ union bpf_attr { * but this is only implemented for native XDP (with driver * support) as of this writing). * - * All values for *flags* are reserved for future usage, and must - * be left at zero. + * The lower two bits of *flags* are used as the return code if + * the map lookup fails. This is so that the return value can be + * one of the XDP program return codes up to XDP_TX, as chosen by + * the caller. Any higher bits in the *flags* argument must be + * unset. * * When used to redirect packets to net devices, this helper * provides a high performance increase over **bpf_redirect**\ (). diff --git a/net/core/filter.c b/net/core/filter.c index b4a062379bb9..4836264f82ee 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -3605,17 +3605,13 @@ static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp, struct bpf_redirect_info *ri) { u32 index = ri->tgt_index; - void *fwd = NULL; + void *fwd = ri->tgt_value; int err; ri->tgt_index = 0; + ri->tgt_value = NULL; WRITE_ONCE(ri->map, NULL); - fwd = __xdp_map_lookup_elem(map, index); - if (unlikely(!fwd)) { - err = -EINVAL; - goto err; - } if (ri->map_to_flush && unlikely(ri->map_to_flush != map)) xdp_do_flush_map(); @@ -3652,18 +3648,13 @@ static int xdp_do_generic_redirect_map(struct net_device *dev, { struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info); u32 index = ri->tgt_index; - void *fwd = NULL; + void *fwd = ri->tgt_value; int err = 0; ri->tgt_index = 0; + ri->tgt_value = NULL; WRITE_ONCE(ri->map, NULL); - fwd = __xdp_map_lookup_elem(map, index); - if (unlikely(!fwd)) { - err = -EINVAL; - goto err; - } - if (map->map_type == BPF_MAP_TYPE_DEVMAP) { struct bpf_dtab_netdev *dst = fwd; @@ -3732,6 +3723,7 @@ BPF_CALL_2(bpf_xdp_redirect, u32, ifindex, u64, flags) ri->flags = flags; ri->tgt_index = ifindex; + ri->tgt_value = NULL; WRITE_ONCE(ri->map, NULL); return XDP_REDIRECT; @@ -3750,9 +3742,21 @@ BPF_CALL_3(bpf_xdp_redirect_map, struct bpf_map *, map, u32, ifindex, { struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info); - if (unlikely(flags)) + /* Lower bits of the flags are used as return code on lookup failure */ + if (unlikely(flags > XDP_TX)) return XDP_ABORTED; + ri->tgt_value = __xdp_map_lookup_elem(map, ifindex); + if (unlikely(!ri->tgt_value)) { + /* If the lookup fails we want to clear out the state in the + * redirect_info struct completely, so that if an eBPF program + * performs multiple lookups, the last one always takes + * precedence. + */ + WRITE_ONCE(ri->map, NULL); + return flags; + } + ri->flags = flags; ri->tgt_index = ifindex; WRITE_ONCE(ri->map, map); -- 2.30.2