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