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 bpf_prog *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 bpf_prog *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 case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */ 185 ctx->seen |= SEEN_XREG; 186 PPC_CMPWI(r_X, 0); 187 if (ctx->pc_ret0 != -1) { 188 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 189 } else { 190 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 191 PPC_LI(r_ret, 0); 192 PPC_JMP(exit_addr); 193 } 194 if (code == (BPF_ALU | BPF_MOD | BPF_X)) { 195 PPC_DIVWU(r_scratch1, r_A, r_X); 196 PPC_MUL(r_scratch1, r_X, r_scratch1); 197 PPC_SUB(r_A, r_A, r_scratch1); 198 } else { 199 PPC_DIVWU(r_A, r_A, r_X); 200 } 201 break; 202 case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */ 203 PPC_LI32(r_scratch2, K); 204 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 205 PPC_MUL(r_scratch1, r_scratch2, r_scratch1); 206 PPC_SUB(r_A, r_A, r_scratch1); 207 break; 208 case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */ 209 if (K == 1) 210 break; 211 PPC_LI32(r_scratch1, K); 212 PPC_DIVWU(r_A, r_A, r_scratch1); 213 break; 214 case BPF_ALU | BPF_AND | BPF_X: 215 ctx->seen |= SEEN_XREG; 216 PPC_AND(r_A, r_A, r_X); 217 break; 218 case BPF_ALU | BPF_AND | BPF_K: 219 if (!IMM_H(K)) 220 PPC_ANDI(r_A, r_A, K); 221 else { 222 PPC_LI32(r_scratch1, K); 223 PPC_AND(r_A, r_A, r_scratch1); 224 } 225 break; 226 case BPF_ALU | BPF_OR | BPF_X: 227 ctx->seen |= SEEN_XREG; 228 PPC_OR(r_A, r_A, r_X); 229 break; 230 case BPF_ALU | BPF_OR | BPF_K: 231 if (IMM_L(K)) 232 PPC_ORI(r_A, r_A, IMM_L(K)); 233 if (K >= 65536) 234 PPC_ORIS(r_A, r_A, IMM_H(K)); 235 break; 236 case BPF_ANC | SKF_AD_ALU_XOR_X: 237 case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */ 238 ctx->seen |= SEEN_XREG; 239 PPC_XOR(r_A, r_A, r_X); 240 break; 241 case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */ 242 if (IMM_L(K)) 243 PPC_XORI(r_A, r_A, IMM_L(K)); 244 if (K >= 65536) 245 PPC_XORIS(r_A, r_A, IMM_H(K)); 246 break; 247 case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */ 248 ctx->seen |= SEEN_XREG; 249 PPC_SLW(r_A, r_A, r_X); 250 break; 251 case BPF_ALU | BPF_LSH | BPF_K: 252 if (K == 0) 253 break; 254 else 255 PPC_SLWI(r_A, r_A, K); 256 break; 257 case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */ 258 ctx->seen |= SEEN_XREG; 259 PPC_SRW(r_A, r_A, r_X); 260 break; 261 case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */ 262 if (K == 0) 263 break; 264 else 265 PPC_SRWI(r_A, r_A, K); 266 break; 267 case BPF_ALU | BPF_NEG: 268 PPC_NEG(r_A, r_A); 269 break; 270 case BPF_RET | BPF_K: 271 PPC_LI32(r_ret, K); 272 if (!K) { 273 if (ctx->pc_ret0 == -1) 274 ctx->pc_ret0 = i; 275 } 276 /* 277 * If this isn't the very last instruction, branch to 278 * the epilogue if we've stuff to clean up. Otherwise, 279 * if there's nothing to tidy, just return. If we /are/ 280 * the last instruction, we're about to fall through to 281 * the epilogue to return. 282 */ 283 if (i != flen - 1) { 284 /* 285 * Note: 'seen' is properly valid only on pass 286 * #2. Both parts of this conditional are the 287 * same instruction size though, meaning the 288 * first pass will still correctly determine the 289 * code size/addresses. 290 */ 291 if (ctx->seen) 292 PPC_JMP(exit_addr); 293 else 294 PPC_BLR(); 295 } 296 break; 297 case BPF_RET | BPF_A: 298 PPC_MR(r_ret, r_A); 299 if (i != flen - 1) { 300 if (ctx->seen) 301 PPC_JMP(exit_addr); 302 else 303 PPC_BLR(); 304 } 305 break; 306 case BPF_MISC | BPF_TAX: /* X = A */ 307 PPC_MR(r_X, r_A); 308 break; 309 case BPF_MISC | BPF_TXA: /* A = X */ 310 ctx->seen |= SEEN_XREG; 311 PPC_MR(r_A, r_X); 312 break; 313 314 /*** Constant loads/M[] access ***/ 315 case BPF_LD | BPF_IMM: /* A = K */ 316 PPC_LI32(r_A, K); 317 break; 318 case BPF_LDX | BPF_IMM: /* X = K */ 319 PPC_LI32(r_X, K); 320 break; 321 case BPF_LD | BPF_MEM: /* A = mem[K] */ 322 PPC_MR(r_A, r_M + (K & 0xf)); 323 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 324 break; 325 case BPF_LDX | BPF_MEM: /* X = mem[K] */ 326 PPC_MR(r_X, r_M + (K & 0xf)); 327 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 328 break; 329 case BPF_ST: /* mem[K] = A */ 330 PPC_MR(r_M + (K & 0xf), r_A); 331 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 332 break; 333 case BPF_STX: /* mem[K] = X */ 334 PPC_MR(r_M + (K & 0xf), r_X); 335 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 336 break; 337 case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */ 338 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 339 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 340 break; 341 case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */ 342 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 343 break; 344 345 /*** Ancillary info loads ***/ 346 case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */ 347 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 348 protocol) != 2); 349 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 350 protocol)); 351 break; 352 case BPF_ANC | SKF_AD_IFINDEX: 353 case BPF_ANC | SKF_AD_HATYPE: 354 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 355 ifindex) != 4); 356 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 357 type) != 2); 358 PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 359 dev)); 360 PPC_CMPDI(r_scratch1, 0); 361 if (ctx->pc_ret0 != -1) { 362 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 363 } else { 364 /* Exit, returning 0; first pass hits here. */ 365 PPC_BCC_SHORT(COND_NE, ctx->idx * 4 + 12); 366 PPC_LI(r_ret, 0); 367 PPC_JMP(exit_addr); 368 } 369 if (code == (BPF_ANC | SKF_AD_IFINDEX)) { 370 PPC_LWZ_OFFS(r_A, r_scratch1, 371 offsetof(struct net_device, ifindex)); 372 } else { 373 PPC_LHZ_OFFS(r_A, r_scratch1, 374 offsetof(struct net_device, type)); 375 } 376 377 break; 378 case BPF_ANC | SKF_AD_MARK: 379 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 380 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 381 mark)); 382 break; 383 case BPF_ANC | SKF_AD_RXHASH: 384 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 385 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 386 hash)); 387 break; 388 case BPF_ANC | SKF_AD_VLAN_TAG: 389 case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT: 390 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 391 BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000); 392 393 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 394 vlan_tci)); 395 if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) { 396 PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT); 397 } else { 398 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT); 399 PPC_SRWI(r_A, r_A, 12); 400 } 401 break; 402 case BPF_ANC | SKF_AD_QUEUE: 403 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 404 queue_mapping) != 2); 405 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 406 queue_mapping)); 407 break; 408 case BPF_ANC | SKF_AD_PKTTYPE: 409 PPC_LBZ_OFFS(r_A, r_skb, PKT_TYPE_OFFSET()); 410 PPC_ANDI(r_A, r_A, PKT_TYPE_MAX); 411 PPC_SRWI(r_A, r_A, 5); 412 break; 413 case BPF_ANC | SKF_AD_CPU: 414 #ifdef CONFIG_SMP 415 /* 416 * PACA ptr is r13: 417 * raw_smp_processor_id() = local_paca->paca_index 418 */ 419 BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct, 420 paca_index) != 2); 421 PPC_LHZ_OFFS(r_A, 13, 422 offsetof(struct paca_struct, paca_index)); 423 #else 424 PPC_LI(r_A, 0); 425 #endif 426 break; 427 428 /*** Absolute loads from packet header/data ***/ 429 case BPF_LD | BPF_W | BPF_ABS: 430 func = CHOOSE_LOAD_FUNC(K, sk_load_word); 431 goto common_load; 432 case BPF_LD | BPF_H | BPF_ABS: 433 func = CHOOSE_LOAD_FUNC(K, sk_load_half); 434 goto common_load; 435 case BPF_LD | BPF_B | BPF_ABS: 436 func = CHOOSE_LOAD_FUNC(K, sk_load_byte); 437 common_load: 438 /* Load from [K]. */ 439 ctx->seen |= SEEN_DATAREF; 440 PPC_LI64(r_scratch1, func); 441 PPC_MTLR(r_scratch1); 442 PPC_LI32(r_addr, K); 443 PPC_BLRL(); 444 /* 445 * Helper returns 'lt' condition on error, and an 446 * appropriate return value in r3 447 */ 448 PPC_BCC(COND_LT, exit_addr); 449 break; 450 451 /*** Indirect loads from packet header/data ***/ 452 case BPF_LD | BPF_W | BPF_IND: 453 func = sk_load_word; 454 goto common_load_ind; 455 case BPF_LD | BPF_H | BPF_IND: 456 func = sk_load_half; 457 goto common_load_ind; 458 case BPF_LD | BPF_B | BPF_IND: 459 func = sk_load_byte; 460 common_load_ind: 461 /* 462 * Load from [X + K]. Negative offsets are tested for 463 * in the helper functions. 464 */ 465 ctx->seen |= SEEN_DATAREF | SEEN_XREG; 466 PPC_LI64(r_scratch1, func); 467 PPC_MTLR(r_scratch1); 468 PPC_ADDI(r_addr, r_X, IMM_L(K)); 469 if (K >= 32768) 470 PPC_ADDIS(r_addr, r_addr, IMM_HA(K)); 471 PPC_BLRL(); 472 /* If error, cr0.LT set */ 473 PPC_BCC(COND_LT, exit_addr); 474 break; 475 476 case BPF_LDX | BPF_B | BPF_MSH: 477 func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh); 478 goto common_load; 479 break; 480 481 /*** Jump and branches ***/ 482 case BPF_JMP | BPF_JA: 483 if (K != 0) 484 PPC_JMP(addrs[i + 1 + K]); 485 break; 486 487 case BPF_JMP | BPF_JGT | BPF_K: 488 case BPF_JMP | BPF_JGT | BPF_X: 489 true_cond = COND_GT; 490 goto cond_branch; 491 case BPF_JMP | BPF_JGE | BPF_K: 492 case BPF_JMP | BPF_JGE | BPF_X: 493 true_cond = COND_GE; 494 goto cond_branch; 495 case BPF_JMP | BPF_JEQ | BPF_K: 496 case BPF_JMP | BPF_JEQ | BPF_X: 497 true_cond = COND_EQ; 498 goto cond_branch; 499 case BPF_JMP | BPF_JSET | BPF_K: 500 case BPF_JMP | BPF_JSET | BPF_X: 501 true_cond = COND_NE; 502 /* Fall through */ 503 cond_branch: 504 /* same targets, can avoid doing the test :) */ 505 if (filter[i].jt == filter[i].jf) { 506 if (filter[i].jt > 0) 507 PPC_JMP(addrs[i + 1 + filter[i].jt]); 508 break; 509 } 510 511 switch (code) { 512 case BPF_JMP | BPF_JGT | BPF_X: 513 case BPF_JMP | BPF_JGE | BPF_X: 514 case BPF_JMP | BPF_JEQ | BPF_X: 515 ctx->seen |= SEEN_XREG; 516 PPC_CMPLW(r_A, r_X); 517 break; 518 case BPF_JMP | BPF_JSET | BPF_X: 519 ctx->seen |= SEEN_XREG; 520 PPC_AND_DOT(r_scratch1, r_A, r_X); 521 break; 522 case BPF_JMP | BPF_JEQ | BPF_K: 523 case BPF_JMP | BPF_JGT | BPF_K: 524 case BPF_JMP | BPF_JGE | BPF_K: 525 if (K < 32768) 526 PPC_CMPLWI(r_A, K); 527 else { 528 PPC_LI32(r_scratch1, K); 529 PPC_CMPLW(r_A, r_scratch1); 530 } 531 break; 532 case BPF_JMP | BPF_JSET | BPF_K: 533 if (K < 32768) 534 /* PPC_ANDI is /only/ dot-form */ 535 PPC_ANDI(r_scratch1, r_A, K); 536 else { 537 PPC_LI32(r_scratch1, K); 538 PPC_AND_DOT(r_scratch1, r_A, 539 r_scratch1); 540 } 541 break; 542 } 543 /* Sometimes branches are constructed "backward", with 544 * the false path being the branch and true path being 545 * a fallthrough to the next instruction. 546 */ 547 if (filter[i].jt == 0) 548 /* Swap the sense of the branch */ 549 PPC_BCC(true_cond ^ COND_CMP_TRUE, 550 addrs[i + 1 + filter[i].jf]); 551 else { 552 PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]); 553 if (filter[i].jf != 0) 554 PPC_JMP(addrs[i + 1 + filter[i].jf]); 555 } 556 break; 557 default: 558 /* The filter contains something cruel & unusual. 559 * We don't handle it, but also there shouldn't be 560 * anything missing from our list. 561 */ 562 if (printk_ratelimit()) 563 pr_err("BPF filter opcode %04x (@%d) unsupported\n", 564 filter[i].code, i); 565 return -ENOTSUPP; 566 } 567 568 } 569 /* Set end-of-body-code address for exit. */ 570 addrs[i] = ctx->idx * 4; 571 572 return 0; 573 } 574 575 void bpf_jit_compile(struct bpf_prog *fp) 576 { 577 unsigned int proglen; 578 unsigned int alloclen; 579 u32 *image = NULL; 580 u32 *code_base; 581 unsigned int *addrs; 582 struct codegen_context cgctx; 583 int pass; 584 int flen = fp->len; 585 586 if (!bpf_jit_enable) 587 return; 588 589 addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL); 590 if (addrs == NULL) 591 return; 592 593 /* 594 * There are multiple assembly passes as the generated code will change 595 * size as it settles down, figuring out the max branch offsets/exit 596 * paths required. 597 * 598 * The range of standard conditional branches is +/- 32Kbytes. Since 599 * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to 600 * finish with 8 bytes/instruction. Not feasible, so long jumps are 601 * used, distinct from short branches. 602 * 603 * Current: 604 * 605 * For now, both branch types assemble to 2 words (short branches padded 606 * with a NOP); this is less efficient, but assembly will always complete 607 * after exactly 3 passes: 608 * 609 * First pass: No code buffer; Program is "faux-generated" -- no code 610 * emitted but maximum size of output determined (and addrs[] filled 611 * in). Also, we note whether we use M[], whether we use skb data, etc. 612 * All generation choices assumed to be 'worst-case', e.g. branches all 613 * far (2 instructions), return path code reduction not available, etc. 614 * 615 * Second pass: Code buffer allocated with size determined previously. 616 * Prologue generated to support features we have seen used. Exit paths 617 * determined and addrs[] is filled in again, as code may be slightly 618 * smaller as a result. 619 * 620 * Third pass: Code generated 'for real', and branch destinations 621 * determined from now-accurate addrs[] map. 622 * 623 * Ideal: 624 * 625 * If we optimise this, near branches will be shorter. On the 626 * first assembly pass, we should err on the side of caution and 627 * generate the biggest code. On subsequent passes, branches will be 628 * generated short or long and code size will reduce. With smaller 629 * code, more branches may fall into the short category, and code will 630 * reduce more. 631 * 632 * Finally, if we see one pass generate code the same size as the 633 * previous pass we have converged and should now generate code for 634 * real. Allocating at the end will also save the memory that would 635 * otherwise be wasted by the (small) current code shrinkage. 636 * Preferably, we should do a small number of passes (e.g. 5) and if we 637 * haven't converged by then, get impatient and force code to generate 638 * as-is, even if the odd branch would be left long. The chances of a 639 * long jump are tiny with all but the most enormous of BPF filter 640 * inputs, so we should usually converge on the third pass. 641 */ 642 643 cgctx.idx = 0; 644 cgctx.seen = 0; 645 cgctx.pc_ret0 = -1; 646 /* Scouting faux-generate pass 0 */ 647 if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) 648 /* We hit something illegal or unsupported. */ 649 goto out; 650 651 /* 652 * Pretend to build prologue, given the features we've seen. This will 653 * update ctgtx.idx as it pretends to output instructions, then we can 654 * calculate total size from idx. 655 */ 656 bpf_jit_build_prologue(fp, 0, &cgctx); 657 bpf_jit_build_epilogue(0, &cgctx); 658 659 proglen = cgctx.idx * 4; 660 alloclen = proglen + FUNCTION_DESCR_SIZE; 661 image = module_alloc(alloclen); 662 if (!image) 663 goto out; 664 665 code_base = image + (FUNCTION_DESCR_SIZE/4); 666 667 /* Code generation passes 1-2 */ 668 for (pass = 1; pass < 3; pass++) { 669 /* Now build the prologue, body code & epilogue for real. */ 670 cgctx.idx = 0; 671 bpf_jit_build_prologue(fp, code_base, &cgctx); 672 bpf_jit_build_body(fp, code_base, &cgctx, addrs); 673 bpf_jit_build_epilogue(code_base, &cgctx); 674 675 if (bpf_jit_enable > 1) 676 pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, 677 proglen - (cgctx.idx * 4), cgctx.seen); 678 } 679 680 if (bpf_jit_enable > 1) 681 /* Note that we output the base address of the code_base 682 * rather than image, since opcodes are in code_base. 683 */ 684 bpf_jit_dump(flen, proglen, pass, code_base); 685 686 if (image) { 687 bpf_flush_icache(code_base, code_base + (proglen/4)); 688 /* Function descriptor nastiness: Address + TOC */ 689 ((u64 *)image)[0] = (u64)code_base; 690 ((u64 *)image)[1] = local_paca->kernel_toc; 691 fp->bpf_func = (void *)image; 692 fp->jited = true; 693 } 694 out: 695 kfree(addrs); 696 return; 697 } 698 699 void bpf_jit_free(struct bpf_prog *fp) 700 { 701 if (fp->jited) 702 module_memfree(fp->bpf_func); 703 704 bpf_prog_unlock_free(fp); 705 } 706