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xdp2skb_meta_kern.c


products/Sources/formale Sprachen/C/Linux/samples/bpf/xdp2skb_meta_kern.c

/* 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, * but instead rely on the iproute2 TC tool for loading BPF-objects. */ #include #include #include /* * 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; 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_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 */

                                                                                                                                                                                                                                                                                                                                                                                                     

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