Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 1 | /* Copyright (c) 2012 The Chromium OS Authors. All rights reserved. |
| 2 | * Use of this source code is governed by a BSD-style license that can be |
| 3 | * found in the LICENSE file. |
| 4 | */ |
| 5 | |
| 6 | #include <stdint.h> |
| 7 | #include <stdio.h> |
| 8 | #include <stdlib.h> |
| 9 | #include <string.h> |
| 10 | |
| 11 | #include "bpf.h" |
| 12 | |
| 13 | /* Common jump targets. */ |
| 14 | #define NEXT 0 |
| 15 | #define SKIP 1 |
| 16 | #define SKIPN(_n) (_n) |
| 17 | |
| 18 | inline size_t set_bpf_instr(struct sock_filter *instr, |
| 19 | unsigned short code, unsigned int k, |
| 20 | unsigned char jt, unsigned char jf) |
| 21 | { |
| 22 | instr->code = code; |
| 23 | instr->k = k; |
| 24 | instr->jt = jt; |
| 25 | instr->jf = jf; |
| 26 | return 1U; |
| 27 | } |
| 28 | |
| 29 | /* Size-aware arg loaders. */ |
| 30 | #if defined(BITS32) |
| 31 | size_t bpf_load_arg(struct sock_filter *filter, int argidx) |
| 32 | { |
| 33 | set_bpf_stmt(filter, BPF_LD+BPF_W+BPF_ABS, LO_ARG(argidx)); |
| 34 | return 1U; |
| 35 | } |
| 36 | #elif defined(BITS64) |
| 37 | size_t bpf_load_arg(struct sock_filter *filter, int argidx) |
| 38 | { |
| 39 | struct sock_filter *curr_block = filter; |
| 40 | set_bpf_stmt(curr_block++, BPF_LD+BPF_W+BPF_ABS, LO_ARG(argidx)); |
| 41 | set_bpf_stmt(curr_block++, BPF_ST, 0); /* lo -> M[0] */ |
| 42 | set_bpf_stmt(curr_block++, BPF_LD+BPF_W+BPF_ABS, HI_ARG(argidx)); |
| 43 | set_bpf_stmt(curr_block++, BPF_ST, 1); /* hi -> M[1] */ |
| 44 | return curr_block - filter; |
| 45 | } |
| 46 | #endif |
| 47 | |
| 48 | /* Size-aware comparisons. */ |
| 49 | size_t bpf_comp_jeq32(struct sock_filter *filter, unsigned int c, |
| 50 | unsigned char jt, unsigned char jf) |
| 51 | { |
| 52 | set_bpf_jump(filter, BPF_JMP+BPF_JEQ+BPF_K, c, jt, jf); |
| 53 | return 1U; |
| 54 | } |
| 55 | |
| 56 | size_t bpf_comp_jeq64(struct sock_filter *filter, uint64_t c, |
| 57 | unsigned char jt, unsigned char jf) |
| 58 | { |
| 59 | unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); |
| 60 | unsigned int hi = (unsigned int)(c >> 32); |
| 61 | |
| 62 | struct sock_filter *curr_block = filter; |
| 63 | |
| 64 | /* bpf_load_arg leaves |hi| in A */ |
| 65 | curr_block += bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf); |
| 66 | set_bpf_stmt(curr_block++, BPF_LD+BPF_MEM, 0); /* swap in lo */ |
| 67 | curr_block += bpf_comp_jeq32(curr_block, lo, jt, jf); |
| 68 | |
| 69 | return curr_block - filter; |
| 70 | } |
| 71 | |
| 72 | #if defined(BITS32) |
| 73 | #define bpf_comp_jeq bpf_comp_jeq32 |
| 74 | |
| 75 | #elif defined(BITS64) |
| 76 | #define bpf_comp_jeq bpf_comp_jeq64 |
| 77 | #endif |
| 78 | |
| 79 | size_t bpf_arg_comp(struct sock_filter **pfilter, |
| 80 | int op, int argidx, unsigned long c, unsigned int label_id) |
| 81 | { |
| 82 | struct sock_filter *filter = calloc(BPF_ARG_COMP_LEN + 1, |
| 83 | sizeof(struct sock_filter)); |
| 84 | struct sock_filter *curr_block = filter; |
| 85 | int flip = 0; |
| 86 | |
| 87 | /* Load arg */ |
| 88 | curr_block += bpf_load_arg(curr_block, argidx); |
| 89 | |
| 90 | /* Jump type */ |
| 91 | switch (op) { |
| 92 | case EQ: |
| 93 | flip = 0; |
| 94 | break; |
| 95 | case NE: |
| 96 | flip = 1; |
| 97 | break; |
| 98 | default: |
| 99 | *pfilter = NULL; |
| 100 | return 0; |
| 101 | } |
| 102 | |
| 103 | /* |
| 104 | * It's easier for the rest of the code to have the true branch |
| 105 | * skip and the false branch fall through. |
| 106 | */ |
| 107 | unsigned char jt = flip ? NEXT : SKIP; |
| 108 | unsigned char jf = flip ? SKIP : NEXT; |
| 109 | curr_block += bpf_comp_jeq(curr_block, c, jt, jf); |
| 110 | curr_block += set_bpf_jump_lbl(curr_block, label_id); |
| 111 | |
| 112 | *pfilter = filter; |
| 113 | return curr_block - filter; |
| 114 | } |
| 115 | |
| 116 | void dump_bpf_filter(struct sock_filter *filter, unsigned short len) |
| 117 | { |
| 118 | int i = 0; |
| 119 | |
| 120 | printf("len == %d\n", len); |
| 121 | printf("filter:\n"); |
| 122 | for (i = 0; i < len; i++) { |
| 123 | printf("%d: \t{ code=%#x, jt=%u, jf=%u, k=%#x \t}\n", |
| 124 | i, filter[i].code, filter[i].jt, filter[i].jf, filter[i].k); |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | void dump_bpf_prog(struct sock_fprog *fprog) |
| 129 | { |
| 130 | struct sock_filter *filter = fprog->filter; |
| 131 | unsigned short len = fprog->len; |
| 132 | dump_bpf_filter(filter, len); |
| 133 | } |
| 134 | |
| 135 | int bpf_resolve_jumps(struct bpf_labels *labels, |
| 136 | struct sock_filter *filter, size_t count) |
| 137 | { |
| 138 | struct sock_filter *begin = filter; |
| 139 | __u8 insn = count - 1; |
| 140 | |
| 141 | if (count < 1) |
| 142 | return -1; |
| 143 | /* |
| 144 | * Walk it once, backwards, to build the label table and do fixups. |
| 145 | * Since backward jumps are disallowed by BPF, this is easy. |
| 146 | */ |
| 147 | for (filter += insn; filter >= begin; --insn, --filter) { |
| 148 | if (filter->code != (BPF_JMP+BPF_JA)) |
| 149 | continue; |
| 150 | switch ((filter->jt<<8)|filter->jf) { |
| 151 | case (JUMP_JT<<8)|JUMP_JF: |
| 152 | if (labels->labels[filter->k].location == 0xffffffff) { |
| 153 | fprintf(stderr, "Unresolved label: '%s'\n", |
| 154 | labels->labels[filter->k].label); |
| 155 | return 1; |
| 156 | } |
| 157 | filter->k = labels->labels[filter->k].location - |
| 158 | (insn + 1); |
| 159 | filter->jt = 0; |
| 160 | filter->jf = 0; |
| 161 | continue; |
| 162 | case (LABEL_JT<<8)|LABEL_JF: |
| 163 | if (labels->labels[filter->k].location != 0xffffffff) { |
| 164 | fprintf(stderr, "Duplicate label use: '%s'\n", |
| 165 | labels->labels[filter->k].label); |
| 166 | return 1; |
| 167 | } |
| 168 | labels->labels[filter->k].location = insn; |
| 169 | filter->k = 0; /* fall through */ |
| 170 | filter->jt = 0; |
| 171 | filter->jf = 0; |
| 172 | continue; |
| 173 | } |
| 174 | } |
| 175 | return 0; |
| 176 | } |
| 177 | |
| 178 | /* Simple lookup table for labels. */ |
| 179 | int bpf_label_id(struct bpf_labels *labels, const char *label) |
| 180 | { |
| 181 | struct __bpf_label *begin = labels->labels, *end; |
| 182 | int id; |
| 183 | if (labels->count == 0) { |
| 184 | begin->label = strndup(label, MAX_BPF_LABEL_LEN); |
| 185 | if (!begin->label) { |
| 186 | return -1; |
| 187 | } |
| 188 | begin->location = 0xffffffff; |
| 189 | labels->count++; |
| 190 | return 0; |
| 191 | } |
| 192 | end = begin + labels->count; |
| 193 | for (id = 0; begin < end; ++begin, ++id) { |
| 194 | if (!strcmp(label, begin->label)) |
| 195 | return id; |
| 196 | } |
| 197 | begin->label = strndup(label, MAX_BPF_LABEL_LEN); |
| 198 | if (!begin->label) { |
| 199 | return -1; |
| 200 | } |
| 201 | begin->location = 0xffffffff; |
| 202 | labels->count++; |
| 203 | return id; |
| 204 | } |
| 205 | |
| 206 | /* Free label strings. */ |
| 207 | void free_label_strings(struct bpf_labels *labels) |
| 208 | { |
| 209 | struct __bpf_label *begin = labels->labels, *end; |
| 210 | |
| 211 | end = begin + labels->count; |
| 212 | for (; begin < end; ++begin) { |
| 213 | if (begin->label) |
| 214 | free((void*)(begin->label)); |
| 215 | } |
| 216 | } |