1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (c) 2017 Facebook 3 */ 4 #include <stddef.h> 5 #include <string.h> 6 #include <linux/bpf.h> 7 #include <linux/if_ether.h> 8 #include <linux/if_packet.h> 9 #include <linux/ip.h> 10 #include <linux/ipv6.h> 11 #include <linux/in.h> 12 #include <linux/tcp.h> 13 #include <linux/pkt_cls.h> 14 #include <bpf/bpf_helpers.h> 15 #include <bpf/bpf_endian.h> 16 17 #define barrier() __asm__ __volatile__("": : :"memory") 18 int _version SEC("version") = 1; 19 20 /* llvm will optimize both subprograms into exactly the same BPF assembly 21 * 22 * Disassembly of section .text: 23 * 24 * 0000000000000000 test_pkt_access_subprog1: 25 * ; return skb->len * 2; 26 * 0: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0) 27 * 1: 64 00 00 00 01 00 00 00 w0 <<= 1 28 * 2: 95 00 00 00 00 00 00 00 exit 29 * 30 * 0000000000000018 test_pkt_access_subprog2: 31 * ; return skb->len * val; 32 * 3: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0) 33 * 4: 64 00 00 00 01 00 00 00 w0 <<= 1 34 * 5: 95 00 00 00 00 00 00 00 exit 35 * 36 * Which makes it an interesting test for BTF-enabled verifier. 37 */ 38 static __attribute__ ((noinline)) 39 int test_pkt_access_subprog1(volatile struct __sk_buff *skb) 40 { 41 return skb->len * 2; 42 } 43 44 static __attribute__ ((noinline)) 45 int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb) 46 { 47 return skb->len * val; 48 } 49 50 #define MAX_STACK (512 - 2 * 32) 51 52 __attribute__ ((noinline)) 53 int get_skb_len(struct __sk_buff *skb) 54 { 55 volatile char buf[MAX_STACK] = {}; 56 57 return skb->len; 58 } 59 60 __attribute__ ((noinline)) 61 int get_constant(long val) 62 { 63 return val - 122; 64 } 65 66 int get_skb_ifindex(int, struct __sk_buff *skb, int); 67 68 __attribute__ ((noinline)) 69 int test_pkt_access_subprog3(int val, struct __sk_buff *skb) 70 { 71 return get_skb_len(skb) * get_skb_ifindex(val, skb, get_constant(123)); 72 } 73 74 __attribute__ ((noinline)) 75 int get_skb_ifindex(int val, struct __sk_buff *skb, int var) 76 { 77 volatile char buf[MAX_STACK] = {}; 78 79 return skb->ifindex * val * var; 80 } 81 82 SEC("classifier/test_pkt_access") 83 int test_pkt_access(struct __sk_buff *skb) 84 { 85 void *data_end = (void *)(long)skb->data_end; 86 void *data = (void *)(long)skb->data; 87 struct ethhdr *eth = (struct ethhdr *)(data); 88 struct tcphdr *tcp = NULL; 89 __u8 proto = 255; 90 __u64 ihl_len; 91 92 if (eth + 1 > data_end) 93 return TC_ACT_SHOT; 94 95 if (eth->h_proto == bpf_htons(ETH_P_IP)) { 96 struct iphdr *iph = (struct iphdr *)(eth + 1); 97 98 if (iph + 1 > data_end) 99 return TC_ACT_SHOT; 100 ihl_len = iph->ihl * 4; 101 proto = iph->protocol; 102 tcp = (struct tcphdr *)((void *)(iph) + ihl_len); 103 } else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) { 104 struct ipv6hdr *ip6h = (struct ipv6hdr *)(eth + 1); 105 106 if (ip6h + 1 > data_end) 107 return TC_ACT_SHOT; 108 ihl_len = sizeof(*ip6h); 109 proto = ip6h->nexthdr; 110 tcp = (struct tcphdr *)((void *)(ip6h) + ihl_len); 111 } 112 113 if (test_pkt_access_subprog1(skb) != skb->len * 2) 114 return TC_ACT_SHOT; 115 if (test_pkt_access_subprog2(2, skb) != skb->len * 2) 116 return TC_ACT_SHOT; 117 if (test_pkt_access_subprog3(3, skb) != skb->len * 3 * skb->ifindex) 118 return TC_ACT_SHOT; 119 if (tcp) { 120 if (((void *)(tcp) + 20) > data_end || proto != 6) 121 return TC_ACT_SHOT; 122 barrier(); /* to force ordering of checks */ 123 if (((void *)(tcp) + 18) > data_end) 124 return TC_ACT_SHOT; 125 if (tcp->urg_ptr == 123) 126 return TC_ACT_OK; 127 } 128 129 return TC_ACT_UNSPEC; 130 } 131