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 #include "util.h" 13 14 /* Architecture validation. */ 15 size_t bpf_validate_arch(struct sock_filter *filter) 16 { 17 struct sock_filter *curr_block = filter; 18 set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, arch_nr); 19 set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, ARCH_NR, SKIP, 20 NEXT); 21 set_bpf_ret_kill(curr_block++); 22 return curr_block - filter; 23 } 24 25 /* Syscall number eval functions. */ 26 size_t bpf_allow_syscall(struct sock_filter *filter, int nr) 27 { 28 struct sock_filter *curr_block = filter; 29 set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP); 30 set_bpf_stmt(curr_block++, BPF_RET + BPF_K, SECCOMP_RET_ALLOW); 31 return curr_block - filter; 32 } 33 34 size_t bpf_allow_syscall_args(struct sock_filter *filter, int nr, 35 unsigned int id) 36 { 37 struct sock_filter *curr_block = filter; 38 set_bpf_jump(curr_block++, BPF_JMP + BPF_JEQ + BPF_K, nr, NEXT, SKIP); 39 set_bpf_jump_lbl(curr_block++, id); 40 return curr_block - filter; 41 } 42 43 /* Size-aware arg loaders. */ 44 #if defined(BITS32) 45 size_t bpf_load_arg(struct sock_filter *filter, int argidx) 46 { 47 set_bpf_stmt(filter, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx)); 48 return 1U; 49 } 50 #elif defined(BITS64) 51 size_t bpf_load_arg(struct sock_filter *filter, int argidx) 52 { 53 struct sock_filter *curr_block = filter; 54 set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, LO_ARG(argidx)); 55 set_bpf_stmt(curr_block++, BPF_ST, 0); /* lo -> M[0] */ 56 set_bpf_stmt(curr_block++, BPF_LD + BPF_W + BPF_ABS, HI_ARG(argidx)); 57 set_bpf_stmt(curr_block++, BPF_ST, 1); /* hi -> M[1] */ 58 return curr_block - filter; 59 } 60 #endif 61 62 /* Size-aware comparisons. */ 63 size_t bpf_comp_jeq32(struct sock_filter *filter, unsigned long c, 64 unsigned char jt, unsigned char jf) 65 { 66 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 67 set_bpf_jump(filter, BPF_JMP + BPF_JEQ + BPF_K, lo, jt, jf); 68 return 1U; 69 } 70 71 /* 72 * On 64 bits, we have to do two 32-bit comparisons. 73 * We jump true when *both* comparisons are true. 74 */ 75 #if defined(BITS64) 76 size_t bpf_comp_jeq64(struct sock_filter *filter, uint64_t c, unsigned char jt, 77 unsigned char jf) 78 { 79 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 80 unsigned int hi = (unsigned int)(c >> 32); 81 82 struct sock_filter *curr_block = filter; 83 84 /* bpf_load_arg leaves |hi| in A */ 85 curr_block += bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf); 86 set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */ 87 curr_block += bpf_comp_jeq32(curr_block, lo, jt, jf); 88 89 return curr_block - filter; 90 } 91 #endif 92 93 size_t bpf_comp_jgt32(struct sock_filter *filter, unsigned long c, 94 unsigned char jt, unsigned char jf) 95 { 96 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 97 set_bpf_jump(filter, BPF_JMP + BPF_JGT + BPF_K, lo, jt, jf); 98 return 1U; 99 } 100 101 size_t bpf_comp_jge32(struct sock_filter *filter, unsigned long c, 102 unsigned char jt, unsigned char jf) 103 { 104 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 105 set_bpf_jump(filter, BPF_JMP + BPF_JGE + BPF_K, lo, jt, jf); 106 return 1U; 107 } 108 109 /* 110 * On 64 bits, we have to do two/three 32-bit comparisons. 111 * We jump true when the |hi| comparison is true *or* |hi| is equal and the 112 * |lo| comparison is true. 113 */ 114 #if defined(BITS64) 115 size_t bpf_comp_jgt64(struct sock_filter *filter, uint64_t c, unsigned char jt, 116 unsigned char jf) 117 { 118 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 119 unsigned int hi = (unsigned int)(c >> 32); 120 121 struct sock_filter *curr_block = filter; 122 123 /* bpf_load_arg leaves |hi| in A. */ 124 if (hi == 0) { 125 curr_block += 126 bpf_comp_jgt32(curr_block, hi, SKIPN(2) + jt, NEXT); 127 } else { 128 curr_block += 129 bpf_comp_jgt32(curr_block, hi, SKIPN(3) + jt, NEXT); 130 curr_block += 131 bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf); 132 } 133 set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */ 134 curr_block += bpf_comp_jgt32(curr_block, lo, jt, jf); 135 136 return curr_block - filter; 137 } 138 139 size_t bpf_comp_jge64(struct sock_filter *filter, uint64_t c, unsigned char jt, 140 unsigned char jf) 141 { 142 unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); 143 unsigned int hi = (unsigned int)(c >> 32); 144 145 struct sock_filter *curr_block = filter; 146 147 /* bpf_load_arg leaves |hi| in A. */ 148 if (hi == 0) { 149 curr_block += 150 bpf_comp_jgt32(curr_block, hi, SKIPN(2) + jt, NEXT); 151 } else { 152 curr_block += 153 bpf_comp_jgt32(curr_block, hi, SKIPN(3) + jt, NEXT); 154 curr_block += 155 bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf); 156 } 157 set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */ 158 curr_block += bpf_comp_jge32(curr_block, lo, jt, jf); 159 160 return curr_block - filter; 161 } 162 #endif 163 164 /* Size-aware bitwise AND. */ 165 size_t bpf_comp_jset32(struct sock_filter *filter, unsigned long mask, 166 unsigned char jt, unsigned char jf) 167 { 168 unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF); 169 set_bpf_jump(filter, BPF_JMP + BPF_JSET + BPF_K, mask_lo, jt, jf); 170 return 1U; 171 } 172 173 /* 174 * On 64 bits, we have to do two 32-bit bitwise ANDs. 175 * We jump true when *either* bitwise AND is true (non-zero). 176 */ 177 #if defined(BITS64) 178 size_t bpf_comp_jset64(struct sock_filter *filter, uint64_t mask, 179 unsigned char jt, unsigned char jf) 180 { 181 unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF); 182 unsigned int mask_hi = (unsigned int)(mask >> 32); 183 184 struct sock_filter *curr_block = filter; 185 186 /* bpf_load_arg leaves |hi| in A */ 187 curr_block += bpf_comp_jset32(curr_block, mask_hi, SKIPN(2) + jt, NEXT); 188 set_bpf_stmt(curr_block++, BPF_LD + BPF_MEM, 0); /* swap in |lo| */ 189 curr_block += bpf_comp_jset32(curr_block, mask_lo, jt, jf); 190 191 return curr_block - filter; 192 } 193 #endif 194 195 size_t bpf_comp_jin(struct sock_filter *filter, unsigned long mask, 196 unsigned char jt, unsigned char jf) 197 { 198 unsigned long negative_mask = ~mask; 199 /* 200 * The mask is negated, so the comparison will be true when the argument 201 * includes a flag that wasn't listed in the original (non-negated) 202 * mask. This would be the failure case, so we switch |jt| and |jf|. 203 */ 204 return bpf_comp_jset(filter, negative_mask, jf, jt); 205 } 206 207 static size_t bpf_arg_comp_len(int op, unsigned long c attribute_unused) 208 { 209 /* The comparisons that use gt/ge internally may have extra opcodes. */ 210 switch (op) { 211 case LT: 212 case LE: 213 case GT: 214 case GE: 215 #if defined(BITS64) 216 /* 217 * |c| can only have a high 32-bit part when running on 64 bits. 218 */ 219 if ((c >> 32) == 0) 220 return BPF_ARG_SHORT_GT_GE_COMP_LEN + 1; 221 #endif 222 return BPF_ARG_GT_GE_COMP_LEN + 1; 223 default: 224 return BPF_ARG_COMP_LEN + 1; 225 } 226 } 227 228 size_t bpf_arg_comp(struct sock_filter **pfilter, int op, int argidx, 229 unsigned long c, unsigned int label_id) 230 { 231 size_t filter_len = bpf_arg_comp_len(op, c); 232 struct sock_filter *filter = 233 calloc(filter_len, sizeof(struct sock_filter)); 234 struct sock_filter *curr_block = filter; 235 size_t (*comp_function)(struct sock_filter * filter, unsigned long k, 236 unsigned char jt, unsigned char jf); 237 int flip = 0; 238 239 /* Load arg */ 240 curr_block += bpf_load_arg(curr_block, argidx); 241 242 /* Jump type */ 243 switch (op) { 244 case EQ: 245 comp_function = bpf_comp_jeq; 246 flip = 0; 247 break; 248 case NE: 249 comp_function = bpf_comp_jeq; 250 flip = 1; 251 break; 252 case LT: 253 comp_function = bpf_comp_jge; 254 flip = 1; 255 break; 256 case LE: 257 comp_function = bpf_comp_jgt; 258 flip = 1; 259 break; 260 case GT: 261 comp_function = bpf_comp_jgt; 262 flip = 0; 263 break; 264 case GE: 265 comp_function = bpf_comp_jge; 266 flip = 0; 267 break; 268 case SET: 269 comp_function = bpf_comp_jset; 270 flip = 0; 271 break; 272 case IN: 273 comp_function = bpf_comp_jin; 274 flip = 0; 275 break; 276 default: 277 *pfilter = NULL; 278 return 0; 279 } 280 281 /* 282 * It's easier for the rest of the code to have the true branch 283 * skip and the false branch fall through. 284 */ 285 unsigned char jt = flip ? NEXT : SKIP; 286 unsigned char jf = flip ? SKIP : NEXT; 287 curr_block += comp_function(curr_block, c, jt, jf); 288 curr_block += set_bpf_jump_lbl(curr_block, label_id); 289 290 *pfilter = filter; 291 return curr_block - filter; 292 } 293 294 int bpf_resolve_jumps(struct bpf_labels *labels, struct sock_filter *filter, 295 size_t len) 296 { 297 struct sock_filter *instr; 298 size_t i, offset; 299 300 if (len > BPF_MAXINSNS) 301 return -1; 302 303 /* 304 * Walk it once, backwards, to build the label table and do fixups. 305 * Since backward jumps are disallowed by BPF, this is easy. 306 */ 307 for (i = 0; i < len; i++) { 308 offset = len - i - 1; 309 instr = &filter[offset]; 310 if (instr->code != (BPF_JMP + BPF_JA)) 311 continue; 312 switch ((instr->jt << 8) | instr->jf) { 313 case (JUMP_JT << 8) | JUMP_JF: 314 if (instr->k >= labels->count) { 315 warn("nonexistent label id: %u", instr->k); 316 return -1; 317 } 318 if (labels->labels[instr->k].location == 0xffffffff) { 319 warn("unresolved label: '%s'", 320 labels->labels[instr->k].label); 321 return -1; 322 } 323 instr->k = 324 labels->labels[instr->k].location - (offset + 1); 325 instr->jt = 0; 326 instr->jf = 0; 327 continue; 328 case (LABEL_JT << 8) | LABEL_JF: 329 if (labels->labels[instr->k].location != 0xffffffff) { 330 warn("duplicate label: '%s'", 331 labels->labels[instr->k].label); 332 return -1; 333 } 334 labels->labels[instr->k].location = offset; 335 instr->k = 0; /* Fall through. */ 336 instr->jt = 0; 337 instr->jf = 0; 338 continue; 339 } 340 } 341 return 0; 342 } 343 344 /* Simple lookup table for labels. */ 345 int bpf_label_id(struct bpf_labels *labels, const char *label) 346 { 347 struct __bpf_label *begin = labels->labels, *end; 348 int id; 349 if (labels->count == 0) { 350 begin->label = strndup(label, MAX_BPF_LABEL_LEN); 351 if (!begin->label) { 352 return -1; 353 } 354 begin->location = 0xffffffff; 355 labels->count++; 356 return 0; 357 } 358 end = begin + labels->count; 359 for (id = 0; begin < end; ++begin, ++id) { 360 if (!strcmp(label, begin->label)) { 361 return id; 362 } 363 } 364 365 /* The label wasn't found. Insert it only if there's space. */ 366 if (labels->count == BPF_LABELS_MAX) { 367 return -1; 368 } 369 begin->label = strndup(label, MAX_BPF_LABEL_LEN); 370 if (!begin->label) { 371 return -1; 372 } 373 begin->location = 0xffffffff; 374 labels->count++; 375 return id; 376 } 377 378 void free_label_strings(struct bpf_labels *labels) 379 { 380 if (labels->count == 0) 381 return; 382 383 struct __bpf_label *begin = labels->labels, *end; 384 385 end = begin + labels->count; 386 for (; begin < end; ++begin) { 387 if (begin->label) 388 free((void *)(begin->label)); 389 } 390 391 labels->count = 0; 392 } 393
