1 /* bpf_jit_comp.c: BPF JIT compiler for PPC64 2 * 3 * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation 4 * 5 * Based on the x86 BPF compiler, by Eric Dumazet (eric.dumazet@gmail.com) 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public License 9 * as published by the Free Software Foundation; version 2 10 * of the License. 11 */ 12 #include <linux/moduleloader.h> 13 #include <asm/cacheflush.h> 14 #include <linux/netdevice.h> 15 #include <linux/filter.h> 16 #include <linux/if_vlan.h> 17 18 #include "bpf_jit.h" 19 20 int bpf_jit_enable __read_mostly; 21 22 static inline void bpf_flush_icache(void *start, void *end) 23 { 24 smp_wmb(); 25 flush_icache_range((unsigned long)start, (unsigned long)end); 26 } 27 28 static void bpf_jit_build_prologue(struct sk_filter *fp, u32 *image, 29 struct codegen_context *ctx) 30 { 31 int i; 32 const struct sock_filter *filter = fp->insns; 33 34 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 35 /* Make stackframe */ 36 if (ctx->seen & SEEN_DATAREF) { 37 /* If we call any helpers (for loads), save LR */ 38 EMIT(PPC_INST_MFLR | __PPC_RT(R0)); 39 PPC_STD(0, 1, 16); 40 41 /* Back up non-volatile regs. */ 42 PPC_STD(r_D, 1, -(8*(32-r_D))); 43 PPC_STD(r_HL, 1, -(8*(32-r_HL))); 44 } 45 if (ctx->seen & SEEN_MEM) { 46 /* 47 * Conditionally save regs r15-r31 as some will be used 48 * for M[] data. 49 */ 50 for (i = r_M; i < (r_M+16); i++) { 51 if (ctx->seen & (1 << (i-r_M))) 52 PPC_STD(i, 1, -(8*(32-i))); 53 } 54 } 55 EMIT(PPC_INST_STDU | __PPC_RS(R1) | __PPC_RA(R1) | 56 (-BPF_PPC_STACKFRAME & 0xfffc)); 57 } 58 59 if (ctx->seen & SEEN_DATAREF) { 60 /* 61 * If this filter needs to access skb data, 62 * prepare r_D and r_HL: 63 * r_HL = skb->len - skb->data_len 64 * r_D = skb->data 65 */ 66 PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 67 data_len)); 68 PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len)); 69 PPC_SUB(r_HL, r_HL, r_scratch1); 70 PPC_LD_OFFS(r_D, r_skb, offsetof(struct sk_buff, data)); 71 } 72 73 if (ctx->seen & SEEN_XREG) { 74 /* 75 * TODO: Could also detect whether first instr. sets X and 76 * avoid this (as below, with A). 77 */ 78 PPC_LI(r_X, 0); 79 } 80 81 switch (filter[0].code) { 82 case BPF_RET | BPF_K: 83 case BPF_LD | BPF_W | BPF_LEN: 84 case BPF_LD | BPF_W | BPF_ABS: 85 case BPF_LD | BPF_H | BPF_ABS: 86 case BPF_LD | BPF_B | BPF_ABS: 87 /* first instruction sets A register (or is RET 'constant') */ 88 break; 89 default: 90 /* make sure we dont leak kernel information to user */ 91 PPC_LI(r_A, 0); 92 } 93 } 94 95 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) 96 { 97 int i; 98 99 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 100 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME); 101 if (ctx->seen & SEEN_DATAREF) { 102 PPC_LD(0, 1, 16); 103 PPC_MTLR(0); 104 PPC_LD(r_D, 1, -(8*(32-r_D))); 105 PPC_LD(r_HL, 1, -(8*(32-r_HL))); 106 } 107 if (ctx->seen & SEEN_MEM) { 108 /* Restore any saved non-vol registers */ 109 for (i = r_M; i < (r_M+16); i++) { 110 if (ctx->seen & (1 << (i-r_M))) 111 PPC_LD(i, 1, -(8*(32-i))); 112 } 113 } 114 } 115 /* The RETs have left a return value in R3. */ 116 117 PPC_BLR(); 118 } 119 120 #define CHOOSE_LOAD_FUNC(K, func) \ 121 ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset) 122 123 /* Assemble the body code between the prologue & epilogue. */ 124 static int bpf_jit_build_body(struct sk_filter *fp, u32 *image, 125 struct codegen_context *ctx, 126 unsigned int *addrs) 127 { 128 const struct sock_filter *filter = fp->insns; 129 int flen = fp->len; 130 u8 *func; 131 unsigned int true_cond; 132 int i; 133 134 /* Start of epilogue code */ 135 unsigned int exit_addr = addrs[flen]; 136 137 for (i = 0; i < flen; i++) { 138 unsigned int K = filter[i].k; 139 u16 code = bpf_anc_helper(&filter[i]); 140 141 /* 142 * addrs[] maps a BPF bytecode address into a real offset from 143 * the start of the body code. 144 */ 145 addrs[i] = ctx->idx * 4; 146 147 switch (code) { 148 /*** ALU ops ***/ 149 case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */ 150 ctx->seen |= SEEN_XREG; 151 PPC_ADD(r_A, r_A, r_X); 152 break; 153 case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */ 154 if (!K) 155 break; 156 PPC_ADDI(r_A, r_A, IMM_L(K)); 157 if (K >= 32768) 158 PPC_ADDIS(r_A, r_A, IMM_HA(K)); 159 break; 160 case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */ 161 ctx->seen |= SEEN_XREG; 162 PPC_SUB(r_A, r_A, r_X); 163 break; 164 case BPF_ALU | BPF_SUB | BPF_K: /* A -= K */ 165 if (!K) 166 break; 167 PPC_ADDI(r_A, r_A, IMM_L(-K)); 168 if (K >= 32768) 169 PPC_ADDIS(r_A, r_A, IMM_HA(-K)); 170 break; 171 case BPF_ALU | BPF_MUL | BPF_X: /* A *= X; */ 172 ctx->seen |= SEEN_XREG; 173 PPC_MUL(r_A, r_A, r_X); 174 break; 175 case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */ 176 if (K < 32768) 177 PPC_MULI(r_A, r_A, K); 178 else { 179 PPC_LI32(r_scratch1, K); 180 PPC_MUL(r_A, r_A, r_scratch1); 181 } 182 break; 183 case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */ 184 ctx->seen |= SEEN_XREG; 185 PPC_CMPWI(r_X, 0); 186 if (ctx->pc_ret0 != -1) { 187 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 188 } else { 189 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 190 PPC_LI(r_ret, 0); 191 PPC_JMP(exit_addr); 192 } 193 PPC_DIVWU(r_scratch1, r_A, r_X); 194 PPC_MUL(r_scratch1, r_X, r_scratch1); 195 PPC_SUB(r_A, r_A, r_scratch1); 196 break; 197 case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */ 198 PPC_LI32(r_scratch2, K); 199 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 200 PPC_MUL(r_scratch1, r_scratch2, r_scratch1); 201 PPC_SUB(r_A, r_A, r_scratch1); 202 break; 203 case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */ 204 ctx->seen |= SEEN_XREG; 205 PPC_CMPWI(r_X, 0); 206 if (ctx->pc_ret0 != -1) { 207 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 208 } else { 209 /* 210 * Exit, returning 0; first pass hits here 211 * (longer worst-case code size). 212 */ 213 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 214 PPC_LI(r_ret, 0); 215 PPC_JMP(exit_addr); 216 } 217 PPC_DIVWU(r_A, r_A, r_X); 218 break; 219 case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */ 220 if (K == 1) 221 break; 222 PPC_LI32(r_scratch1, K); 223 PPC_DIVWU(r_A, r_A, r_scratch1); 224 break; 225 case BPF_ALU | BPF_AND | BPF_X: 226 ctx->seen |= SEEN_XREG; 227 PPC_AND(r_A, r_A, r_X); 228 break; 229 case BPF_ALU | BPF_AND | BPF_K: 230 if (!IMM_H(K)) 231 PPC_ANDI(r_A, r_A, K); 232 else { 233 PPC_LI32(r_scratch1, K); 234 PPC_AND(r_A, r_A, r_scratch1); 235 } 236 break; 237 case BPF_ALU | BPF_OR | BPF_X: 238 ctx->seen |= SEEN_XREG; 239 PPC_OR(r_A, r_A, r_X); 240 break; 241 case BPF_ALU | BPF_OR | BPF_K: 242 if (IMM_L(K)) 243 PPC_ORI(r_A, r_A, IMM_L(K)); 244 if (K >= 65536) 245 PPC_ORIS(r_A, r_A, IMM_H(K)); 246 break; 247 case BPF_ANC | SKF_AD_ALU_XOR_X: 248 case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */ 249 ctx->seen |= SEEN_XREG; 250 PPC_XOR(r_A, r_A, r_X); 251 break; 252 case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */ 253 if (IMM_L(K)) 254 PPC_XORI(r_A, r_A, IMM_L(K)); 255 if (K >= 65536) 256 PPC_XORIS(r_A, r_A, IMM_H(K)); 257 break; 258 case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */ 259 ctx->seen |= SEEN_XREG; 260 PPC_SLW(r_A, r_A, r_X); 261 break; 262 case BPF_ALU | BPF_LSH | BPF_K: 263 if (K == 0) 264 break; 265 else 266 PPC_SLWI(r_A, r_A, K); 267 break; 268 case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */ 269 ctx->seen |= SEEN_XREG; 270 PPC_SRW(r_A, r_A, r_X); 271 break; 272 case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */ 273 if (K == 0) 274 break; 275 else 276 PPC_SRWI(r_A, r_A, K); 277 break; 278 case BPF_ALU | BPF_NEG: 279 PPC_NEG(r_A, r_A); 280 break; 281 case BPF_RET | BPF_K: 282 PPC_LI32(r_ret, K); 283 if (!K) { 284 if (ctx->pc_ret0 == -1) 285 ctx->pc_ret0 = i; 286 } 287 /* 288 * If this isn't the very last instruction, branch to 289 * the epilogue if we've stuff to clean up. Otherwise, 290 * if there's nothing to tidy, just return. If we /are/ 291 * the last instruction, we're about to fall through to 292 * the epilogue to return. 293 */ 294 if (i != flen - 1) { 295 /* 296 * Note: 'seen' is properly valid only on pass 297 * #2. Both parts of this conditional are the 298 * same instruction size though, meaning the 299 * first pass will still correctly determine the 300 * code size/addresses. 301 */ 302 if (ctx->seen) 303 PPC_JMP(exit_addr); 304 else 305 PPC_BLR(); 306 } 307 break; 308 case BPF_RET | BPF_A: 309 PPC_MR(r_ret, r_A); 310 if (i != flen - 1) { 311 if (ctx->seen) 312 PPC_JMP(exit_addr); 313 else 314 PPC_BLR(); 315 } 316 break; 317 case BPF_MISC | BPF_TAX: /* X = A */ 318 PPC_MR(r_X, r_A); 319 break; 320 case BPF_MISC | BPF_TXA: /* A = X */ 321 ctx->seen |= SEEN_XREG; 322 PPC_MR(r_A, r_X); 323 break; 324 325 /*** Constant loads/M[] access ***/ 326 case BPF_LD | BPF_IMM: /* A = K */ 327 PPC_LI32(r_A, K); 328 break; 329 case BPF_LDX | BPF_IMM: /* X = K */ 330 PPC_LI32(r_X, K); 331 break; 332 case BPF_LD | BPF_MEM: /* A = mem[K] */ 333 PPC_MR(r_A, r_M + (K & 0xf)); 334 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 335 break; 336 case BPF_LDX | BPF_MEM: /* X = mem[K] */ 337 PPC_MR(r_X, r_M + (K & 0xf)); 338 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 339 break; 340 case BPF_ST: /* mem[K] = A */ 341 PPC_MR(r_M + (K & 0xf), r_A); 342 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 343 break; 344 case BPF_STX: /* mem[K] = X */ 345 PPC_MR(r_M + (K & 0xf), r_X); 346 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 347 break; 348 case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */ 349 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 350 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 351 break; 352 case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */ 353 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 354 break; 355 356 /*** Ancillary info loads ***/ 357 case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */ 358 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 359 protocol) != 2); 360 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 361 protocol)); 362 break; 363 case BPF_ANC | SKF_AD_IFINDEX: 364 PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 365 dev)); 366 PPC_CMPDI(r_scratch1, 0); 367 if (ctx->pc_ret0 != -1) { 368 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 369 } else { 370 /* Exit, returning 0; first pass hits here. */ 371 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 372 PPC_LI(r_ret, 0); 373 PPC_JMP(exit_addr); 374 } 375 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 376 ifindex) != 4); 377 PPC_LWZ_OFFS(r_A, r_scratch1, 378 offsetof(struct net_device, ifindex)); 379 break; 380 case BPF_ANC | SKF_AD_MARK: 381 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 382 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 383 mark)); 384 break; 385 case BPF_ANC | SKF_AD_RXHASH: 386 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 387 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 388 hash)); 389 break; 390 case BPF_ANC | SKF_AD_VLAN_TAG: 391 case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT: 392 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 393 BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000); 394 395 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 396 vlan_tci)); 397 if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) { 398 PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT); 399 } else { 400 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT); 401 PPC_SRWI(r_A, r_A, 12); 402 } 403 break; 404 case BPF_ANC | SKF_AD_QUEUE: 405 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 406 queue_mapping) != 2); 407 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 408 queue_mapping)); 409 break; 410 case BPF_ANC | SKF_AD_CPU: 411 #ifdef CONFIG_SMP 412 /* 413 * PACA ptr is r13: 414 * raw_smp_processor_id() = local_paca->paca_index 415 */ 416 BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct, 417 paca_index) != 2); 418 PPC_LHZ_OFFS(r_A, 13, 419 offsetof(struct paca_struct, paca_index)); 420 #else 421 PPC_LI(r_A, 0); 422 #endif 423 break; 424 425 /*** Absolute loads from packet header/data ***/ 426 case BPF_LD | BPF_W | BPF_ABS: 427 func = CHOOSE_LOAD_FUNC(K, sk_load_word); 428 goto common_load; 429 case BPF_LD | BPF_H | BPF_ABS: 430 func = CHOOSE_LOAD_FUNC(K, sk_load_half); 431 goto common_load; 432 case BPF_LD | BPF_B | BPF_ABS: 433 func = CHOOSE_LOAD_FUNC(K, sk_load_byte); 434 common_load: 435 /* Load from [K]. */ 436 ctx->seen |= SEEN_DATAREF; 437 PPC_LI64(r_scratch1, func); 438 PPC_MTLR(r_scratch1); 439 PPC_LI32(r_addr, K); 440 PPC_BLRL(); 441 /* 442 * Helper returns 'lt' condition on error, and an 443 * appropriate return value in r3 444 */ 445 PPC_BCC(COND_LT, exit_addr); 446 break; 447 448 /*** Indirect loads from packet header/data ***/ 449 case BPF_LD | BPF_W | BPF_IND: 450 func = sk_load_word; 451 goto common_load_ind; 452 case BPF_LD | BPF_H | BPF_IND: 453 func = sk_load_half; 454 goto common_load_ind; 455 case BPF_LD | BPF_B | BPF_IND: 456 func = sk_load_byte; 457 common_load_ind: 458 /* 459 * Load from [X + K]. Negative offsets are tested for 460 * in the helper functions. 461 */ 462 ctx->seen |= SEEN_DATAREF | SEEN_XREG; 463 PPC_LI64(r_scratch1, func); 464 PPC_MTLR(r_scratch1); 465 PPC_ADDI(r_addr, r_X, IMM_L(K)); 466 if (K >= 32768) 467 PPC_ADDIS(r_addr, r_addr, IMM_HA(K)); 468 PPC_BLRL(); 469 /* If error, cr0.LT set */ 470 PPC_BCC(COND_LT, exit_addr); 471 break; 472 473 case BPF_LDX | BPF_B | BPF_MSH: 474 func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh); 475 goto common_load; 476 break; 477 478 /*** Jump and branches ***/ 479 case BPF_JMP | BPF_JA: 480 if (K != 0) 481 PPC_JMP(addrs[i + 1 + K]); 482 break; 483 484 case BPF_JMP | BPF_JGT | BPF_K: 485 case BPF_JMP | BPF_JGT | BPF_X: 486 true_cond = COND_GT; 487 goto cond_branch; 488 case BPF_JMP | BPF_JGE | BPF_K: 489 case BPF_JMP | BPF_JGE | BPF_X: 490 true_cond = COND_GE; 491 goto cond_branch; 492 case BPF_JMP | BPF_JEQ | BPF_K: 493 case BPF_JMP | BPF_JEQ | BPF_X: 494 true_cond = COND_EQ; 495 goto cond_branch; 496 case BPF_JMP | BPF_JSET | BPF_K: 497 case BPF_JMP | BPF_JSET | BPF_X: 498 true_cond = COND_NE; 499 /* Fall through */ 500 cond_branch: 501 /* same targets, can avoid doing the test :) */ 502 if (filter[i].jt == filter[i].jf) { 503 if (filter[i].jt > 0) 504 PPC_JMP(addrs[i + 1 + filter[i].jt]); 505 break; 506 } 507 508 switch (code) { 509 case BPF_JMP | BPF_JGT | BPF_X: 510 case BPF_JMP | BPF_JGE | BPF_X: 511 case BPF_JMP | BPF_JEQ | BPF_X: 512 ctx->seen |= SEEN_XREG; 513 PPC_CMPLW(r_A, r_X); 514 break; 515 case BPF_JMP | BPF_JSET | BPF_X: 516 ctx->seen |= SEEN_XREG; 517 PPC_AND_DOT(r_scratch1, r_A, r_X); 518 break; 519 case BPF_JMP | BPF_JEQ | BPF_K: 520 case BPF_JMP | BPF_JGT | BPF_K: 521 case BPF_JMP | BPF_JGE | BPF_K: 522 if (K < 32768) 523 PPC_CMPLWI(r_A, K); 524 else { 525 PPC_LI32(r_scratch1, K); 526 PPC_CMPLW(r_A, r_scratch1); 527 } 528 break; 529 case BPF_JMP | BPF_JSET | BPF_K: 530 if (K < 32768) 531 /* PPC_ANDI is /only/ dot-form */ 532 PPC_ANDI(r_scratch1, r_A, K); 533 else { 534 PPC_LI32(r_scratch1, K); 535 PPC_AND_DOT(r_scratch1, r_A, 536 r_scratch1); 537 } 538 break; 539 } 540 /* Sometimes branches are constructed "backward", with 541 * the false path being the branch and true path being 542 * a fallthrough to the next instruction. 543 */ 544 if (filter[i].jt == 0) 545 /* Swap the sense of the branch */ 546 PPC_BCC(true_cond ^ COND_CMP_TRUE, 547 addrs[i + 1 + filter[i].jf]); 548 else { 549 PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]); 550 if (filter[i].jf != 0) 551 PPC_JMP(addrs[i + 1 + filter[i].jf]); 552 } 553 break; 554 default: 555 /* The filter contains something cruel & unusual. 556 * We don't handle it, but also there shouldn't be 557 * anything missing from our list. 558 */ 559 if (printk_ratelimit()) 560 pr_err("BPF filter opcode %04x (@%d) unsupported\n", 561 filter[i].code, i); 562 return -ENOTSUPP; 563 } 564 565 } 566 /* Set end-of-body-code address for exit. */ 567 addrs[i] = ctx->idx * 4; 568 569 return 0; 570 } 571 572 void bpf_jit_compile(struct sk_filter *fp) 573 { 574 unsigned int proglen; 575 unsigned int alloclen; 576 u32 *image = NULL; 577 u32 *code_base; 578 unsigned int *addrs; 579 struct codegen_context cgctx; 580 int pass; 581 int flen = fp->len; 582 583 if (!bpf_jit_enable) 584 return; 585 586 addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL); 587 if (addrs == NULL) 588 return; 589 590 /* 591 * There are multiple assembly passes as the generated code will change 592 * size as it settles down, figuring out the max branch offsets/exit 593 * paths required. 594 * 595 * The range of standard conditional branches is +/- 32Kbytes. Since 596 * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to 597 * finish with 8 bytes/instruction. Not feasible, so long jumps are 598 * used, distinct from short branches. 599 * 600 * Current: 601 * 602 * For now, both branch types assemble to 2 words (short branches padded 603 * with a NOP); this is less efficient, but assembly will always complete 604 * after exactly 3 passes: 605 * 606 * First pass: No code buffer; Program is "faux-generated" -- no code 607 * emitted but maximum size of output determined (and addrs[] filled 608 * in). Also, we note whether we use M[], whether we use skb data, etc. 609 * All generation choices assumed to be 'worst-case', e.g. branches all 610 * far (2 instructions), return path code reduction not available, etc. 611 * 612 * Second pass: Code buffer allocated with size determined previously. 613 * Prologue generated to support features we have seen used. Exit paths 614 * determined and addrs[] is filled in again, as code may be slightly 615 * smaller as a result. 616 * 617 * Third pass: Code generated 'for real', and branch destinations 618 * determined from now-accurate addrs[] map. 619 * 620 * Ideal: 621 * 622 * If we optimise this, near branches will be shorter. On the 623 * first assembly pass, we should err on the side of caution and 624 * generate the biggest code. On subsequent passes, branches will be 625 * generated short or long and code size will reduce. With smaller 626 * code, more branches may fall into the short category, and code will 627 * reduce more. 628 * 629 * Finally, if we see one pass generate code the same size as the 630 * previous pass we have converged and should now generate code for 631 * real. Allocating at the end will also save the memory that would 632 * otherwise be wasted by the (small) current code shrinkage. 633 * Preferably, we should do a small number of passes (e.g. 5) and if we 634 * haven't converged by then, get impatient and force code to generate 635 * as-is, even if the odd branch would be left long. The chances of a 636 * long jump are tiny with all but the most enormous of BPF filter 637 * inputs, so we should usually converge on the third pass. 638 */ 639 640 cgctx.idx = 0; 641 cgctx.seen = 0; 642 cgctx.pc_ret0 = -1; 643 /* Scouting faux-generate pass 0 */ 644 if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) 645 /* We hit something illegal or unsupported. */ 646 goto out; 647 648 /* 649 * Pretend to build prologue, given the features we've seen. This will 650 * update ctgtx.idx as it pretends to output instructions, then we can 651 * calculate total size from idx. 652 */ 653 bpf_jit_build_prologue(fp, 0, &cgctx); 654 bpf_jit_build_epilogue(0, &cgctx); 655 656 proglen = cgctx.idx * 4; 657 alloclen = proglen + FUNCTION_DESCR_SIZE; 658 image = module_alloc(alloclen); 659 if (!image) 660 goto out; 661 662 code_base = image + (FUNCTION_DESCR_SIZE/4); 663 664 /* Code generation passes 1-2 */ 665 for (pass = 1; pass < 3; pass++) { 666 /* Now build the prologue, body code & epilogue for real. */ 667 cgctx.idx = 0; 668 bpf_jit_build_prologue(fp, code_base, &cgctx); 669 bpf_jit_build_body(fp, code_base, &cgctx, addrs); 670 bpf_jit_build_epilogue(code_base, &cgctx); 671 672 if (bpf_jit_enable > 1) 673 pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, 674 proglen - (cgctx.idx * 4), cgctx.seen); 675 } 676 677 if (bpf_jit_enable > 1) 678 /* Note that we output the base address of the code_base 679 * rather than image, since opcodes are in code_base. 680 */ 681 bpf_jit_dump(flen, proglen, pass, code_base); 682 683 if (image) { 684 bpf_flush_icache(code_base, code_base + (proglen/4)); 685 /* Function descriptor nastiness: Address + TOC */ 686 ((u64 *)image)[0] = (u64)code_base; 687 ((u64 *)image)[1] = local_paca->kernel_toc; 688 fp->bpf_func = (void *)image; 689 fp->jited = 1; 690 } 691 out: 692 kfree(addrs); 693 return; 694 } 695 696 void bpf_jit_free(struct sk_filter *fp) 697 { 698 if (fp->jited) 699 module_free(NULL, fp->bpf_func); 700 kfree(fp); 701 } 702