// SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2019 Facebook */ #include <linux/bpf.h> #include "bpf_helpers.h" #include "bpf_trace_helpers.h" struct sk_buff { unsigned int len; }; __u64 test_result = 0; BPF_TRACE_2("fexit/test_pkt_access", test_main, struct sk_buff *, skb, int, ret) { int len; __builtin_preserve_access_index(({ len = skb->len; })); if (len != 74 || ret != 0) return 0; test_result = 1; return 0; } __u64 test_result_subprog1 = 0; BPF_TRACE_2("fexit/test_pkt_access_subprog1", test_subprog1, struct sk_buff *, skb, int, ret) { int len; __builtin_preserve_access_index(({ len = skb->len; })); if (len != 74 || ret != 148) return 0; test_result_subprog1 = 1; return 0; } /* Though test_pkt_access_subprog2() is defined in C as: * static __attribute__ ((noinline)) * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb) * { * return skb->len * val; * } * llvm optimizations remove 'int val' argument and generate BPF assembly: * r0 = *(u32 *)(r1 + 0) * w0 <<= 1 * exit * In such case the verifier falls back to conservative and * tracing program can access arguments and return value as u64 * instead of accurate types. */ struct args_subprog2 { __u64 args[5]; __u64 ret; }; __u64 test_result_subprog2 = 0; SEC("fexit/test_pkt_access_subprog2") int test_subprog2(struct args_subprog2 *ctx) { struct sk_buff *skb = (void *)ctx->args[0]; __u64 ret; int len; bpf_probe_read_kernel(&len, sizeof(len), __builtin_preserve_access_index(&skb->len)); ret = ctx->ret; /* bpf_prog_load() loads "test_pkt_access.o" with BPF_F_TEST_RND_HI32 * which randomizes upper 32 bits after BPF_ALU32 insns. * Hence after 'w0 <<= 1' upper bits of $rax are random. * That is expected and correct. Trim them. */ ret = (__u32) ret; if (len != 74 || ret != 148) return 0; test_result_subprog2 = 1; return 0; } char _license[] SEC("license") = "GPL";