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_S_RET_K: 83 case BPF_S_LD_W_LEN: 84 case BPF_S_ANC_PROTOCOL: 85 case BPF_S_ANC_IFINDEX: 86 case BPF_S_ANC_MARK: 87 case BPF_S_ANC_RXHASH: 88 case BPF_S_ANC_VLAN_TAG: 89 case BPF_S_ANC_VLAN_TAG_PRESENT: 90 case BPF_S_ANC_CPU: 91 case BPF_S_ANC_QUEUE: 92 case BPF_S_LD_W_ABS: 93 case BPF_S_LD_H_ABS: 94 case BPF_S_LD_B_ABS: 95 /* first instruction sets A register (or is RET 'constant') */ 96 break; 97 default: 98 /* make sure we dont leak kernel information to user */ 99 PPC_LI(r_A, 0); 100 } 101 } 102 103 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) 104 { 105 int i; 106 107 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 108 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME); 109 if (ctx->seen & SEEN_DATAREF) { 110 PPC_LD(0, 1, 16); 111 PPC_MTLR(0); 112 PPC_LD(r_D, 1, -(8*(32-r_D))); 113 PPC_LD(r_HL, 1, -(8*(32-r_HL))); 114 } 115 if (ctx->seen & SEEN_MEM) { 116 /* Restore any saved non-vol registers */ 117 for (i = r_M; i < (r_M+16); i++) { 118 if (ctx->seen & (1 << (i-r_M))) 119 PPC_LD(i, 1, -(8*(32-i))); 120 } 121 } 122 } 123 /* The RETs have left a return value in R3. */ 124 125 PPC_BLR(); 126 } 127 128 #define CHOOSE_LOAD_FUNC(K, func) \ 129 ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset) 130 131 /* Assemble the body code between the prologue & epilogue. */ 132 static int bpf_jit_build_body(struct sk_filter *fp, u32 *image, 133 struct codegen_context *ctx, 134 unsigned int *addrs) 135 { 136 const struct sock_filter *filter = fp->insns; 137 int flen = fp->len; 138 u8 *func; 139 unsigned int true_cond; 140 int i; 141 142 /* Start of epilogue code */ 143 unsigned int exit_addr = addrs[flen]; 144 145 for (i = 0; i < flen; i++) { 146 unsigned int K = filter[i].k; 147 148 /* 149 * addrs[] maps a BPF bytecode address into a real offset from 150 * the start of the body code. 151 */ 152 addrs[i] = ctx->idx * 4; 153 154 switch (filter[i].code) { 155 /*** ALU ops ***/ 156 case BPF_S_ALU_ADD_X: /* A += X; */ 157 ctx->seen |= SEEN_XREG; 158 PPC_ADD(r_A, r_A, r_X); 159 break; 160 case BPF_S_ALU_ADD_K: /* A += K; */ 161 if (!K) 162 break; 163 PPC_ADDI(r_A, r_A, IMM_L(K)); 164 if (K >= 32768) 165 PPC_ADDIS(r_A, r_A, IMM_HA(K)); 166 break; 167 case BPF_S_ALU_SUB_X: /* A -= X; */ 168 ctx->seen |= SEEN_XREG; 169 PPC_SUB(r_A, r_A, r_X); 170 break; 171 case BPF_S_ALU_SUB_K: /* A -= K */ 172 if (!K) 173 break; 174 PPC_ADDI(r_A, r_A, IMM_L(-K)); 175 if (K >= 32768) 176 PPC_ADDIS(r_A, r_A, IMM_HA(-K)); 177 break; 178 case BPF_S_ALU_MUL_X: /* A *= X; */ 179 ctx->seen |= SEEN_XREG; 180 PPC_MUL(r_A, r_A, r_X); 181 break; 182 case BPF_S_ALU_MUL_K: /* A *= K */ 183 if (K < 32768) 184 PPC_MULI(r_A, r_A, K); 185 else { 186 PPC_LI32(r_scratch1, K); 187 PPC_MUL(r_A, r_A, r_scratch1); 188 } 189 break; 190 case BPF_S_ALU_MOD_X: /* A %= X; */ 191 ctx->seen |= SEEN_XREG; 192 PPC_CMPWI(r_X, 0); 193 if (ctx->pc_ret0 != -1) { 194 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 195 } else { 196 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 197 PPC_LI(r_ret, 0); 198 PPC_JMP(exit_addr); 199 } 200 PPC_DIVWU(r_scratch1, r_A, r_X); 201 PPC_MUL(r_scratch1, r_X, r_scratch1); 202 PPC_SUB(r_A, r_A, r_scratch1); 203 break; 204 case BPF_S_ALU_MOD_K: /* A %= K; */ 205 PPC_LI32(r_scratch2, K); 206 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 207 PPC_MUL(r_scratch1, r_scratch2, r_scratch1); 208 PPC_SUB(r_A, r_A, r_scratch1); 209 break; 210 case BPF_S_ALU_DIV_X: /* A /= X; */ 211 ctx->seen |= SEEN_XREG; 212 PPC_CMPWI(r_X, 0); 213 if (ctx->pc_ret0 != -1) { 214 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 215 } else { 216 /* 217 * Exit, returning 0; first pass hits here 218 * (longer worst-case code size). 219 */ 220 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 221 PPC_LI(r_ret, 0); 222 PPC_JMP(exit_addr); 223 } 224 PPC_DIVWU(r_A, r_A, r_X); 225 break; 226 case BPF_S_ALU_DIV_K: /* A /= K */ 227 if (K == 1) 228 break; 229 PPC_LI32(r_scratch1, K); 230 PPC_DIVWU(r_A, r_A, r_scratch1); 231 break; 232 case BPF_S_ALU_AND_X: 233 ctx->seen |= SEEN_XREG; 234 PPC_AND(r_A, r_A, r_X); 235 break; 236 case BPF_S_ALU_AND_K: 237 if (!IMM_H(K)) 238 PPC_ANDI(r_A, r_A, K); 239 else { 240 PPC_LI32(r_scratch1, K); 241 PPC_AND(r_A, r_A, r_scratch1); 242 } 243 break; 244 case BPF_S_ALU_OR_X: 245 ctx->seen |= SEEN_XREG; 246 PPC_OR(r_A, r_A, r_X); 247 break; 248 case BPF_S_ALU_OR_K: 249 if (IMM_L(K)) 250 PPC_ORI(r_A, r_A, IMM_L(K)); 251 if (K >= 65536) 252 PPC_ORIS(r_A, r_A, IMM_H(K)); 253 break; 254 case BPF_S_ANC_ALU_XOR_X: 255 case BPF_S_ALU_XOR_X: /* A ^= X */ 256 ctx->seen |= SEEN_XREG; 257 PPC_XOR(r_A, r_A, r_X); 258 break; 259 case BPF_S_ALU_XOR_K: /* A ^= K */ 260 if (IMM_L(K)) 261 PPC_XORI(r_A, r_A, IMM_L(K)); 262 if (K >= 65536) 263 PPC_XORIS(r_A, r_A, IMM_H(K)); 264 break; 265 case BPF_S_ALU_LSH_X: /* A <<= X; */ 266 ctx->seen |= SEEN_XREG; 267 PPC_SLW(r_A, r_A, r_X); 268 break; 269 case BPF_S_ALU_LSH_K: 270 if (K == 0) 271 break; 272 else 273 PPC_SLWI(r_A, r_A, K); 274 break; 275 case BPF_S_ALU_RSH_X: /* A >>= X; */ 276 ctx->seen |= SEEN_XREG; 277 PPC_SRW(r_A, r_A, r_X); 278 break; 279 case BPF_S_ALU_RSH_K: /* A >>= K; */ 280 if (K == 0) 281 break; 282 else 283 PPC_SRWI(r_A, r_A, K); 284 break; 285 case BPF_S_ALU_NEG: 286 PPC_NEG(r_A, r_A); 287 break; 288 case BPF_S_RET_K: 289 PPC_LI32(r_ret, K); 290 if (!K) { 291 if (ctx->pc_ret0 == -1) 292 ctx->pc_ret0 = i; 293 } 294 /* 295 * If this isn't the very last instruction, branch to 296 * the epilogue if we've stuff to clean up. Otherwise, 297 * if there's nothing to tidy, just return. If we /are/ 298 * the last instruction, we're about to fall through to 299 * the epilogue to return. 300 */ 301 if (i != flen - 1) { 302 /* 303 * Note: 'seen' is properly valid only on pass 304 * #2. Both parts of this conditional are the 305 * same instruction size though, meaning the 306 * first pass will still correctly determine the 307 * code size/addresses. 308 */ 309 if (ctx->seen) 310 PPC_JMP(exit_addr); 311 else 312 PPC_BLR(); 313 } 314 break; 315 case BPF_S_RET_A: 316 PPC_MR(r_ret, r_A); 317 if (i != flen - 1) { 318 if (ctx->seen) 319 PPC_JMP(exit_addr); 320 else 321 PPC_BLR(); 322 } 323 break; 324 case BPF_S_MISC_TAX: /* X = A */ 325 PPC_MR(r_X, r_A); 326 break; 327 case BPF_S_MISC_TXA: /* A = X */ 328 ctx->seen |= SEEN_XREG; 329 PPC_MR(r_A, r_X); 330 break; 331 332 /*** Constant loads/M[] access ***/ 333 case BPF_S_LD_IMM: /* A = K */ 334 PPC_LI32(r_A, K); 335 break; 336 case BPF_S_LDX_IMM: /* X = K */ 337 PPC_LI32(r_X, K); 338 break; 339 case BPF_S_LD_MEM: /* A = mem[K] */ 340 PPC_MR(r_A, r_M + (K & 0xf)); 341 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 342 break; 343 case BPF_S_LDX_MEM: /* X = mem[K] */ 344 PPC_MR(r_X, r_M + (K & 0xf)); 345 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 346 break; 347 case BPF_S_ST: /* mem[K] = A */ 348 PPC_MR(r_M + (K & 0xf), r_A); 349 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 350 break; 351 case BPF_S_STX: /* mem[K] = X */ 352 PPC_MR(r_M + (K & 0xf), r_X); 353 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 354 break; 355 case BPF_S_LD_W_LEN: /* A = skb->len; */ 356 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 357 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 358 break; 359 case BPF_S_LDX_W_LEN: /* X = skb->len; */ 360 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 361 break; 362 363 /*** Ancillary info loads ***/ 364 case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */ 365 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 366 protocol) != 2); 367 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 368 protocol)); 369 break; 370 case BPF_S_ANC_IFINDEX: 371 PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 372 dev)); 373 PPC_CMPDI(r_scratch1, 0); 374 if (ctx->pc_ret0 != -1) { 375 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 376 } else { 377 /* Exit, returning 0; first pass hits here. */ 378 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 379 PPC_LI(r_ret, 0); 380 PPC_JMP(exit_addr); 381 } 382 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 383 ifindex) != 4); 384 PPC_LWZ_OFFS(r_A, r_scratch1, 385 offsetof(struct net_device, ifindex)); 386 break; 387 case BPF_S_ANC_MARK: 388 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 389 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 390 mark)); 391 break; 392 case BPF_S_ANC_RXHASH: 393 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 394 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 395 hash)); 396 break; 397 case BPF_S_ANC_VLAN_TAG: 398 case BPF_S_ANC_VLAN_TAG_PRESENT: 399 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 400 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 401 vlan_tci)); 402 if (filter[i].code == BPF_S_ANC_VLAN_TAG) 403 PPC_ANDI(r_A, r_A, VLAN_VID_MASK); 404 else 405 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT); 406 break; 407 case BPF_S_ANC_QUEUE: 408 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 409 queue_mapping) != 2); 410 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 411 queue_mapping)); 412 break; 413 case BPF_S_ANC_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_S_LD_W_ABS: 430 func = CHOOSE_LOAD_FUNC(K, sk_load_word); 431 goto common_load; 432 case BPF_S_LD_H_ABS: 433 func = CHOOSE_LOAD_FUNC(K, sk_load_half); 434 goto common_load; 435 case BPF_S_LD_B_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_S_LD_W_IND: 453 func = sk_load_word; 454 goto common_load_ind; 455 case BPF_S_LD_H_IND: 456 func = sk_load_half; 457 goto common_load_ind; 458 case BPF_S_LD_B_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_S_LDX_B_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_S_JMP_JA: 483 if (K != 0) 484 PPC_JMP(addrs[i + 1 + K]); 485 break; 486 487 case BPF_S_JMP_JGT_K: 488 case BPF_S_JMP_JGT_X: 489 true_cond = COND_GT; 490 goto cond_branch; 491 case BPF_S_JMP_JGE_K: 492 case BPF_S_JMP_JGE_X: 493 true_cond = COND_GE; 494 goto cond_branch; 495 case BPF_S_JMP_JEQ_K: 496 case BPF_S_JMP_JEQ_X: 497 true_cond = COND_EQ; 498 goto cond_branch; 499 case BPF_S_JMP_JSET_K: 500 case BPF_S_JMP_JSET_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 (filter[i].code) { 512 case BPF_S_JMP_JGT_X: 513 case BPF_S_JMP_JGE_X: 514 case BPF_S_JMP_JEQ_X: 515 ctx->seen |= SEEN_XREG; 516 PPC_CMPLW(r_A, r_X); 517 break; 518 case BPF_S_JMP_JSET_X: 519 ctx->seen |= SEEN_XREG; 520 PPC_AND_DOT(r_scratch1, r_A, r_X); 521 break; 522 case BPF_S_JMP_JEQ_K: 523 case BPF_S_JMP_JGT_K: 524 case BPF_S_JMP_JGE_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_S_JMP_JSET_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 sk_filter *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 = 1; 693 } 694 out: 695 kfree(addrs); 696 return; 697 } 698 699 void bpf_jit_free(struct sk_filter *fp) 700 { 701 if (fp->jited) 702 module_free(NULL, fp->bpf_func); 703 kfree(fp); 704 } 705