180 lines · c
1// SPDX-License-Identifier: GPL-2.02/* Copyright (c) 2019 Facebook */3#include <linux/stddef.h>4#include <linux/if_ether.h>5#include <linux/ipv6.h>6#include <linux/bpf.h>7#include <linux/tcp.h>8#include <bpf/bpf_helpers.h>9#include <bpf/bpf_endian.h>10#include <bpf/bpf_tracing.h>11 12struct sk_buff {13 unsigned int len;14};15 16__u64 test_result = 0;17SEC("fexit/test_pkt_access")18int BPF_PROG(test_main, struct sk_buff *skb, int ret)19{20 int len;21 22 __builtin_preserve_access_index(({23 len = skb->len;24 }));25 if (len != 74 || ret != 0)26 return 0;27 test_result = 1;28 return 0;29}30 31__u64 test_result_subprog1 = 0;32SEC("fexit/test_pkt_access_subprog1")33int BPF_PROG(test_subprog1, struct sk_buff *skb, int ret)34{35 int len;36 37 __builtin_preserve_access_index(({38 len = skb->len;39 }));40 if (len != 74 || ret != 148)41 return 0;42 test_result_subprog1 = 1;43 return 0;44}45 46/* Though test_pkt_access_subprog2() is defined in C as:47 * static __attribute__ ((noinline))48 * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)49 * {50 * return skb->len * val;51 * }52 * llvm optimizations remove 'int val' argument and generate BPF assembly:53 * r0 = *(u32 *)(r1 + 0)54 * w0 <<= 155 * exit56 * In such case the verifier falls back to conservative and57 * tracing program can access arguments and return value as u6458 * instead of accurate types.59 */60struct args_subprog2 {61 __u64 args[5];62 __u64 ret;63};64__u64 test_result_subprog2 = 0;65SEC("fexit/test_pkt_access_subprog2")66int test_subprog2(struct args_subprog2 *ctx)67{68 struct sk_buff *skb = (void *)ctx->args[0];69 __u64 ret;70 int len;71 72 bpf_probe_read_kernel(&len, sizeof(len),73 __builtin_preserve_access_index(&skb->len));74 75 ret = ctx->ret;76 /* bpf_prog_test_load() loads "test_pkt_access.bpf.o" with77 * BPF_F_TEST_RND_HI32 which randomizes upper 32 bits after BPF_ALU3278 * insns. Hence after 'w0 <<= 1' upper bits of $rax are random. That is79 * expected and correct. Trim them.80 */81 ret = (__u32) ret;82 if (len != 74 || ret != 148)83 return 0;84 test_result_subprog2 = 1;85 return 0;86}87 88__u64 test_result_subprog3 = 0;89SEC("fexit/test_pkt_access_subprog3")90int BPF_PROG(test_subprog3, int val, struct sk_buff *skb, int ret)91{92 int len;93 94 __builtin_preserve_access_index(({95 len = skb->len;96 }));97 if (len != 74 || ret != 74 * val || val != 3)98 return 0;99 test_result_subprog3 = 1;100 return 0;101}102 103__u64 test_get_skb_len = 0;104SEC("freplace/get_skb_len")105int new_get_skb_len(struct __sk_buff *skb)106{107 int len = skb->len;108 109 if (len != 74)110 return 0;111 test_get_skb_len = 1;112 return 74; /* original get_skb_len() returns skb->len */113}114 115__u64 test_get_skb_ifindex = 0;116SEC("freplace/get_skb_ifindex")117int new_get_skb_ifindex(int val, struct __sk_buff *skb, int var)118{119 void *data_end = (void *)(long)skb->data_end;120 void *data = (void *)(long)skb->data;121 struct ipv6hdr ip6, *ip6p;122 int ifindex = skb->ifindex;123 124 /* check that BPF extension can read packet via direct packet access */125 if (data + 14 + sizeof(ip6) > data_end)126 return 0;127 ip6p = data + 14;128 129 if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))130 return 0;131 132 /* check that legacy packet access helper works too */133 if (bpf_skb_load_bytes(skb, 14, &ip6, sizeof(ip6)) < 0)134 return 0;135 ip6p = &ip6;136 if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))137 return 0;138 139 if (ifindex != 1 || val != 3 || var != 1)140 return 0;141 test_get_skb_ifindex = 1;142 return 3; /* original get_skb_ifindex() returns val * ifindex * var */143}144 145volatile __u64 test_get_constant = 0;146SEC("freplace/get_constant")147int new_get_constant(long val)148{149 if (val != 123)150 return 0;151 test_get_constant = 1;152 return test_get_constant; /* original get_constant() returns val - 122 */153}154 155__u64 test_pkt_write_access_subprog = 0;156SEC("freplace/test_pkt_write_access_subprog")157int new_test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)158{159 160 void *data = (void *)(long)skb->data;161 void *data_end = (void *)(long)skb->data_end;162 struct tcphdr *tcp;163 164 if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))165 return -1;166 167 tcp = data + off;168 if (tcp + 1 > data_end)169 return -1;170 171 /* make modifications to the packet data */172 tcp->check++;173 tcp->syn = 0;174 175 test_pkt_write_access_subprog = 1;176 return 0;177}178 179char _license[] SEC("license") = "GPL";180