netdev - [PATCH net-next 3/4] bpf: devmap: implement devmap prog execution for generic XDP

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Date:   Mon, 21 Jun 2021 05:01:59 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     netdev@...r.kernel.org
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, bpf@...r.kernel.org
Subject: [PATCH net-next 3/4] bpf: devmap: implement devmap prog execution for generic XDP

This lifts the restriction on running devmap BPF progs in generic
redirect mode. To match native XDP behavior, it is invoked right before
generic_xdp_tx is called, and only supports XDP_PASS/XDP_ABORTED/
XDP_DROP actions.

We also return 0 even if devmap program drops the packet, as
semantically redirect has already succeeded and the devmap prog is the
last point before TX of the packet to device where it can deliver a
verdict on the packet.

This also means it must take care of freeing the skb, as
xdp_do_generic_redirect callers only do that in case an error is
returned.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
---
 kernel/bpf/devmap.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 2a75e6c2d27d..db3ed8b20c8c 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -322,7 +322,8 @@ bool dev_map_can_have_prog(struct bpf_map *map)
 {
 	if ((map->map_type == BPF_MAP_TYPE_DEVMAP ||
 	     map->map_type == BPF_MAP_TYPE_DEVMAP_HASH) &&
-	    map->value_size != offsetofend(struct bpf_devmap_val, ifindex))
+	    map->value_size != offsetofend(struct bpf_devmap_val, ifindex) &&
+	    map->value_size != offsetofend(struct bpf_devmap_val, bpf_prog.fd))
 		return true;
 
 	return false;
@@ -499,6 +500,37 @@ static inline int __xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
 	return 0;
 }
 
+static u32 dev_map_bpf_prog_run_skb(struct sk_buff *skb, struct bpf_prog *xdp_prog)
+{
+	struct xdp_txq_info txq = { .dev = skb->dev };
+	struct xdp_buff xdp;
+	u32 act;
+
+	if (!xdp_prog)
+		return XDP_PASS;
+
+	__skb_pull(skb, skb->mac_len);
+	xdp.txq = &txq;
+
+	act = bpf_prog_run_generic_xdp(skb, &xdp, xdp_prog);
+	switch (act) {
+	case XDP_PASS:
+		__skb_push(skb, skb->mac_len);
+		break;
+	default:
+		bpf_warn_invalid_xdp_action(act);
+		fallthrough;
+	case XDP_ABORTED:
+		trace_xdp_exception(skb->dev, xdp_prog, act);
+		fallthrough;
+	case XDP_DROP:
+		kfree_skb(skb);
+		break;
+	}
+
+	return act;
+}
+
 int dev_xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
 		    struct net_device *dev_rx)
 {
@@ -615,6 +647,14 @@ int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
 	if (unlikely(err))
 		return err;
 	skb->dev = dst->dev;
+
+	/* Redirect has already succeeded semantically at this point, so we just
+	 * return 0 even if packet is dropped. Helper below takes care of
+	 * freeing skb.
+	 */
+	if (dev_map_bpf_prog_run_skb(skb, dst->xdp_prog) != XDP_PASS)
+		return 0;
+
 	generic_xdp_tx(skb, xdp_prog);
 
 	return 0;
-- 
2.31.1