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Diffstat (limited to '')
| -rw-r--r-- | samples/bpf/xdp2skb_meta_kern.c | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/samples/bpf/xdp2skb_meta_kern.c b/samples/bpf/xdp2skb_meta_kern.c new file mode 100644 index 000000000..9b783316e --- /dev/null +++ b/samples/bpf/xdp2skb_meta_kern.c @@ -0,0 +1,105 @@ +/* SPDX-License-Identifier: GPL-2.0 + * Copyright (c) 2018 Jesper Dangaard Brouer, Red Hat Inc. + * + * Example howto transfer info from XDP to SKB, e.g. skb->mark + * ----------------------------------------------------------- + * This uses the XDP data_meta infrastructure, and is a cooperation + * between two bpf-programs (1) XDP and (2) clsact at TC-ingress hook. + * + * Notice: This example does not use the BPF C-loader (bpf_load.c), + * but instead rely on the iproute2 TC tool for loading BPF-objects. + */ +#include <uapi/linux/bpf.h> +#include <uapi/linux/pkt_cls.h> + +#include <bpf/bpf_helpers.h> + +/* + * This struct is stored in the XDP 'data_meta' area, which is located + * just in-front-of the raw packet payload data. The meaning is + * specific to these two BPF programs that use it as a communication + * channel. XDP adjust/increase the area via a bpf-helper, and TC use + * boundary checks to see if data have been provided. + * + * The struct must be 4 byte aligned, which here is enforced by the + * struct __attribute__((aligned(4))). + */ +struct meta_info { + __u32 mark; +} __attribute__((aligned(4))); + +SEC("xdp_mark") +int _xdp_mark(struct xdp_md *ctx) +{ + struct meta_info *meta; + void *data, *data_end; + int ret; + + /* Reserve space in-front of data pointer for our meta info. + * (Notice drivers not supporting data_meta will fail here!) + */ + ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta)); + if (ret < 0) + return XDP_ABORTED; + + /* Notice: Kernel-side verifier requires that loading of + * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(), + * as pkt-data pointers are invalidated. Helpers that require + * this are determined/marked by bpf_helper_changes_pkt_data() + */ + data = (void *)(unsigned long)ctx->data; + + /* Check data_meta have room for meta_info struct */ + meta = (void *)(unsigned long)ctx->data_meta; + if (meta + 1 > data) + return XDP_ABORTED; + + meta->mark = 42; + + return XDP_PASS; +} + +SEC("tc_mark") +int _tc_mark(struct __sk_buff *ctx) +{ + void *data = (void *)(unsigned long)ctx->data; + void *data_end = (void *)(unsigned long)ctx->data_end; + void *data_meta = (void *)(unsigned long)ctx->data_meta; + struct meta_info *meta = data_meta; + + /* Check XDP gave us some data_meta */ + if (meta + 1 > data) { + ctx->mark = 41; + /* Skip "accept" if no data_meta is avail */ + return TC_ACT_OK; + } + + /* Hint: See func tc_cls_act_is_valid_access() for BPF_WRITE access */ + ctx->mark = meta->mark; /* Transfer XDP-mark to SKB-mark */ + + return TC_ACT_OK; +} + +/* Manually attaching these programs: +export DEV=ixgbe2 +export FILE=xdp2skb_meta_kern.o + +# via TC command +tc qdisc del dev $DEV clsact 2> /dev/null +tc qdisc add dev $DEV clsact +tc filter add dev $DEV ingress prio 1 handle 1 bpf da obj $FILE sec tc_mark +tc filter show dev $DEV ingress + +# XDP via IP command: +ip link set dev $DEV xdp off +ip link set dev $DEV xdp obj $FILE sec xdp_mark + +# Use iptable to "see" if SKBs are marked +iptables -I INPUT -p icmp -m mark --mark 41 # == 0x29 +iptables -I INPUT -p icmp -m mark --mark 42 # == 0x2a + +# Hint: catch XDP_ABORTED errors via +perf record -e xdp:* +perf script + +*/ |