1 // SPDX-License-Identifier: GPL-2.0 2 /* Copyright (c) 2019 Facebook */ 3 #include <linux/bpf.h> 4 #include "bpf_helpers.h" 5 #include "bpf_trace_helpers.h" 6 7 struct sk_buff { 8 unsigned int len; 9 }; 10 11 __u64 test_result = 0; 12 BPF_TRACE_2("fexit/test_pkt_access", test_main, 13 struct sk_buff *, skb, int, ret) 14 { 15 int len; 16 17 __builtin_preserve_access_index(({ 18 len = skb->len; 19 })); 20 if (len != 74 || ret != 0) 21 return 0; 22 test_result = 1; 23 return 0; 24 } 25 26 __u64 test_result_subprog1 = 0; 27 BPF_TRACE_2("fexit/test_pkt_access_subprog1", test_subprog1, 28 struct sk_buff *, skb, int, ret) 29 { 30 int len; 31 32 __builtin_preserve_access_index(({ 33 len = skb->len; 34 })); 35 if (len != 74 || ret != 148) 36 return 0; 37 test_result_subprog1 = 1; 38 return 0; 39 } 40 41 /* Though test_pkt_access_subprog2() is defined in C as: 42 * static __attribute__ ((noinline)) 43 * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb) 44 * { 45 * return skb->len * val; 46 * } 47 * llvm optimizations remove 'int val' argument and generate BPF assembly: 48 * r0 = *(u32 *)(r1 + 0) 49 * w0 <<= 1 50 * exit 51 * In such case the verifier falls back to conservative and 52 * tracing program can access arguments and return value as u64 53 * instead of accurate types. 54 */ 55 struct args_subprog2 { 56 __u64 args[5]; 57 __u64 ret; 58 }; 59 __u64 test_result_subprog2 = 0; 60 SEC("fexit/test_pkt_access_subprog2") 61 int test_subprog2(struct args_subprog2 *ctx) 62 { 63 struct sk_buff *skb = (void *)ctx->args[0]; 64 __u64 ret; 65 int len; 66 67 bpf_probe_read_kernel(&len, sizeof(len), 68 __builtin_preserve_access_index(&skb->len)); 69 70 ret = ctx->ret; 71 /* bpf_prog_load() loads "test_pkt_access.o" with BPF_F_TEST_RND_HI32 72 * which randomizes upper 32 bits after BPF_ALU32 insns. 73 * Hence after 'w0 <<= 1' upper bits of $rax are random. 74 * That is expected and correct. Trim them. 75 */ 76 ret = (__u32) ret; 77 if (len != 74 || ret != 148) 78 return 0; 79 test_result_subprog2 = 1; 80 return 0; 81 } 82 char _license[] SEC("license") = "GPL"; 83