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1/* SPDX-License-Identifier: GPL-2.02 * Copyright (c) 2018 Jesper Dangaard Brouer, Red Hat Inc.3 *4 * Example howto transfer info from XDP to SKB, e.g. skb->mark5 * -----------------------------------------------------------6 * This uses the XDP data_meta infrastructure, and is a cooperation7 * between two bpf-programs (1) XDP and (2) clsact at TC-ingress hook.8 *9 * Notice: This example does not use the BPF C-loader,10 * but instead rely on the iproute2 TC tool for loading BPF-objects.11 */12#include <uapi/linux/bpf.h>13#include <uapi/linux/pkt_cls.h>14 15#include <bpf/bpf_helpers.h>16 17/*18 * This struct is stored in the XDP 'data_meta' area, which is located19 * just in-front-of the raw packet payload data. The meaning is20 * specific to these two BPF programs that use it as a communication21 * channel. XDP adjust/increase the area via a bpf-helper, and TC use22 * boundary checks to see if data have been provided.23 *24 * The struct must be 4 byte aligned, which here is enforced by the25 * struct __attribute__((aligned(4))).26 */27struct meta_info {28 __u32 mark;29} __attribute__((aligned(4)));30 31SEC("xdp_mark")32int _xdp_mark(struct xdp_md *ctx)33{34 struct meta_info *meta;35 void *data, *data_end;36 int ret;37 38 /* Reserve space in-front of data pointer for our meta info.39 * (Notice drivers not supporting data_meta will fail here!)40 */41 ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta));42 if (ret < 0)43 return XDP_ABORTED;44 45 /* Notice: Kernel-side verifier requires that loading of46 * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(),47 * as pkt-data pointers are invalidated. Helpers that require48 * this are determined/marked by bpf_helper_changes_pkt_data()49 */50 data = (void *)(unsigned long)ctx->data;51 52 /* Check data_meta have room for meta_info struct */53 meta = (void *)(unsigned long)ctx->data_meta;54 if (meta + 1 > data)55 return XDP_ABORTED;56 57 meta->mark = 42;58 59 return XDP_PASS;60}61 62SEC("tc_mark")63int _tc_mark(struct __sk_buff *ctx)64{65 void *data = (void *)(unsigned long)ctx->data;66 void *data_end = (void *)(unsigned long)ctx->data_end;67 void *data_meta = (void *)(unsigned long)ctx->data_meta;68 struct meta_info *meta = data_meta;69 70 /* Check XDP gave us some data_meta */71 if (meta + 1 > data) {72 ctx->mark = 41;73 /* Skip "accept" if no data_meta is avail */74 return TC_ACT_OK;75 }76 77 /* Hint: See func tc_cls_act_is_valid_access() for BPF_WRITE access */78 ctx->mark = meta->mark; /* Transfer XDP-mark to SKB-mark */79 80 return TC_ACT_OK;81}82 83/* Manually attaching these programs:84export DEV=ixgbe285export FILE=xdp2skb_meta_kern.o86 87# via TC command88tc qdisc del dev $DEV clsact 2> /dev/null89tc qdisc add dev $DEV clsact90tc filter add dev $DEV ingress prio 1 handle 1 bpf da obj $FILE sec tc_mark91tc filter show dev $DEV ingress92 93# XDP via IP command:94ip link set dev $DEV xdp off95ip link set dev $DEV xdp obj $FILE sec xdp_mark96 97# Use iptable to "see" if SKBs are marked98iptables -I INPUT -p icmp -m mark --mark 41 # == 0x2999iptables -I INPUT -p icmp -m mark --mark 42 # == 0x2a100 101# Hint: catch XDP_ABORTED errors via102perf record -e xdp:*103perf script104 105*/106