148 lines
3.6 KiB
C
148 lines
3.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2017 Facebook
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*/
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#include <stddef.h>
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#include <string.h>
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#include <linux/bpf.h>
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#include <linux/if_ether.h>
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#include <linux/if_packet.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include <linux/in.h>
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#include <linux/tcp.h>
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#include <linux/pkt_cls.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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/* llvm will optimize both subprograms into exactly the same BPF assembly
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*
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* Disassembly of section .text:
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*
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* 0000000000000000 test_pkt_access_subprog1:
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* ; return skb->len * 2;
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* 0: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0)
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* 1: 64 00 00 00 01 00 00 00 w0 <<= 1
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* 2: 95 00 00 00 00 00 00 00 exit
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*
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* 0000000000000018 test_pkt_access_subprog2:
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* ; return skb->len * val;
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* 3: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0)
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* 4: 64 00 00 00 01 00 00 00 w0 <<= 1
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* 5: 95 00 00 00 00 00 00 00 exit
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*
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* Which makes it an interesting test for BTF-enabled verifier.
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*/
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static __attribute__ ((noinline))
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int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
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{
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return skb->len * 2;
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}
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static __attribute__ ((noinline))
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int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
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{
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return skb->len * val;
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}
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#define MAX_STACK (512 - 2 * 32)
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__attribute__ ((noinline))
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int get_skb_len(struct __sk_buff *skb)
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{
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volatile char buf[MAX_STACK] = {};
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return skb->len;
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}
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__attribute__ ((noinline))
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int get_constant(long val)
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{
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return val - 122;
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}
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int get_skb_ifindex(int, struct __sk_buff *skb, int);
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__attribute__ ((noinline))
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int test_pkt_access_subprog3(int val, struct __sk_buff *skb)
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{
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return get_skb_len(skb) * get_skb_ifindex(val, skb, get_constant(123));
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}
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__attribute__ ((noinline))
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int get_skb_ifindex(int val, struct __sk_buff *skb, int var)
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{
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volatile char buf[MAX_STACK] = {};
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return skb->ifindex * val * var;
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}
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__attribute__ ((noinline))
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int test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
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{
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void *data = (void *)(long)skb->data;
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void *data_end = (void *)(long)skb->data_end;
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struct tcphdr *tcp = NULL;
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if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
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return -1;
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tcp = data + off;
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if (tcp + 1 > data_end)
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return -1;
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/* make modification to the packet data */
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tcp->check++;
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return 0;
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}
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SEC("tc")
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int test_pkt_access(struct __sk_buff *skb)
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{
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void *data_end = (void *)(long)skb->data_end;
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void *data = (void *)(long)skb->data;
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struct ethhdr *eth = (struct ethhdr *)(data);
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struct tcphdr *tcp = NULL;
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__u8 proto = 255;
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__u64 ihl_len;
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if (eth + 1 > data_end)
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return TC_ACT_SHOT;
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if (eth->h_proto == bpf_htons(ETH_P_IP)) {
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struct iphdr *iph = (struct iphdr *)(eth + 1);
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if (iph + 1 > data_end)
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return TC_ACT_SHOT;
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ihl_len = iph->ihl * 4;
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proto = iph->protocol;
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tcp = (struct tcphdr *)((void *)(iph) + ihl_len);
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} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
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struct ipv6hdr *ip6h = (struct ipv6hdr *)(eth + 1);
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if (ip6h + 1 > data_end)
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return TC_ACT_SHOT;
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ihl_len = sizeof(*ip6h);
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proto = ip6h->nexthdr;
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tcp = (struct tcphdr *)((void *)(ip6h) + ihl_len);
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}
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if (test_pkt_access_subprog1(skb) != skb->len * 2)
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return TC_ACT_SHOT;
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if (test_pkt_access_subprog2(2, skb) != skb->len * 2)
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return TC_ACT_SHOT;
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if (test_pkt_access_subprog3(3, skb) != skb->len * 3 * skb->ifindex)
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return TC_ACT_SHOT;
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if (tcp) {
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if (test_pkt_write_access_subprog(skb, (void *)tcp - data))
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return TC_ACT_SHOT;
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if (((void *)(tcp) + 20) > data_end || proto != 6)
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return TC_ACT_SHOT;
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barrier(); /* to force ordering of checks */
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if (((void *)(tcp) + 18) > data_end)
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return TC_ACT_SHOT;
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if (tcp->urg_ptr == 123)
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return TC_ACT_OK;
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}
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return TC_ACT_UNSPEC;
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}
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