1 /* bpf_jit_comp.c: BPF JIT compiler 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 * Ported to ppc32 by Denis Kirjanov <kda@linux-powerpc.org> 7 * 8 * This program is free software; you can redistribute it and/or 9 * modify it under the terms of the GNU General Public License 10 * as published by the Free Software Foundation; version 2 11 * of the License. 12 */ 13 #include <linux/moduleloader.h> 14 #include <asm/cacheflush.h> 15 #include <linux/netdevice.h> 16 #include <linux/filter.h> 17 #include <linux/if_vlan.h> 18 19 #include "bpf_jit.h" 20 21 int bpf_jit_enable __read_mostly; 22 23 static inline void bpf_flush_icache(void *start, void *end) 24 { 25 smp_wmb(); 26 flush_icache_range((unsigned long)start, (unsigned long)end); 27 } 28 29 static void bpf_jit_build_prologue(struct bpf_prog *fp, u32 *image, 30 struct codegen_context *ctx) 31 { 32 int i; 33 const struct sock_filter *filter = fp->insns; 34 35 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 36 /* Make stackframe */ 37 if (ctx->seen & SEEN_DATAREF) { 38 /* If we call any helpers (for loads), save LR */ 39 EMIT(PPC_INST_MFLR | __PPC_RT(R0)); 40 PPC_BPF_STL(0, 1, PPC_LR_STKOFF); 41 42 /* Back up non-volatile regs. */ 43 PPC_BPF_STL(r_D, 1, -(REG_SZ*(32-r_D))); 44 PPC_BPF_STL(r_HL, 1, -(REG_SZ*(32-r_HL))); 45 } 46 if (ctx->seen & SEEN_MEM) { 47 /* 48 * Conditionally save regs r15-r31 as some will be used 49 * for M[] data. 50 */ 51 for (i = r_M; i < (r_M+16); i++) { 52 if (ctx->seen & (1 << (i-r_M))) 53 PPC_BPF_STL(i, 1, -(REG_SZ*(32-i))); 54 } 55 } 56 PPC_BPF_STLU(1, 1, -BPF_PPC_STACKFRAME); 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_LL_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 /* make sure we dont leak kernel information to user */ 82 if (bpf_needs_clear_a(&filter[0])) 83 PPC_LI(r_A, 0); 84 } 85 86 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) 87 { 88 int i; 89 90 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 91 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME); 92 if (ctx->seen & SEEN_DATAREF) { 93 PPC_BPF_LL(0, 1, PPC_LR_STKOFF); 94 PPC_MTLR(0); 95 PPC_BPF_LL(r_D, 1, -(REG_SZ*(32-r_D))); 96 PPC_BPF_LL(r_HL, 1, -(REG_SZ*(32-r_HL))); 97 } 98 if (ctx->seen & SEEN_MEM) { 99 /* Restore any saved non-vol registers */ 100 for (i = r_M; i < (r_M+16); i++) { 101 if (ctx->seen & (1 << (i-r_M))) 102 PPC_BPF_LL(i, 1, -(REG_SZ*(32-i))); 103 } 104 } 105 } 106 /* The RETs have left a return value in R3. */ 107 108 PPC_BLR(); 109 } 110 111 #define CHOOSE_LOAD_FUNC(K, func) \ 112 ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset) 113 114 /* Assemble the body code between the prologue & epilogue. */ 115 static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 116 struct codegen_context *ctx, 117 unsigned int *addrs) 118 { 119 const struct sock_filter *filter = fp->insns; 120 int flen = fp->len; 121 u8 *func; 122 unsigned int true_cond; 123 int i; 124 125 /* Start of epilogue code */ 126 unsigned int exit_addr = addrs[flen]; 127 128 for (i = 0; i < flen; i++) { 129 unsigned int K = filter[i].k; 130 u16 code = bpf_anc_helper(&filter[i]); 131 132 /* 133 * addrs[] maps a BPF bytecode address into a real offset from 134 * the start of the body code. 135 */ 136 addrs[i] = ctx->idx * 4; 137 138 switch (code) { 139 /*** ALU ops ***/ 140 case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */ 141 ctx->seen |= SEEN_XREG; 142 PPC_ADD(r_A, r_A, r_X); 143 break; 144 case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */ 145 if (!K) 146 break; 147 PPC_ADDI(r_A, r_A, IMM_L(K)); 148 if (K >= 32768) 149 PPC_ADDIS(r_A, r_A, IMM_HA(K)); 150 break; 151 case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */ 152 ctx->seen |= SEEN_XREG; 153 PPC_SUB(r_A, r_A, r_X); 154 break; 155 case BPF_ALU | BPF_SUB | BPF_K: /* A -= K */ 156 if (!K) 157 break; 158 PPC_ADDI(r_A, r_A, IMM_L(-K)); 159 if (K >= 32768) 160 PPC_ADDIS(r_A, r_A, IMM_HA(-K)); 161 break; 162 case BPF_ALU | BPF_MUL | BPF_X: /* A *= X; */ 163 ctx->seen |= SEEN_XREG; 164 PPC_MUL(r_A, r_A, r_X); 165 break; 166 case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */ 167 if (K < 32768) 168 PPC_MULI(r_A, r_A, K); 169 else { 170 PPC_LI32(r_scratch1, K); 171 PPC_MUL(r_A, r_A, r_scratch1); 172 } 173 break; 174 case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */ 175 case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */ 176 ctx->seen |= SEEN_XREG; 177 PPC_CMPWI(r_X, 0); 178 if (ctx->pc_ret0 != -1) { 179 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 180 } else { 181 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 182 PPC_LI(r_ret, 0); 183 PPC_JMP(exit_addr); 184 } 185 if (code == (BPF_ALU | BPF_MOD | BPF_X)) { 186 PPC_DIVWU(r_scratch1, r_A, r_X); 187 PPC_MUL(r_scratch1, r_X, r_scratch1); 188 PPC_SUB(r_A, r_A, r_scratch1); 189 } else { 190 PPC_DIVWU(r_A, r_A, r_X); 191 } 192 break; 193 case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */ 194 PPC_LI32(r_scratch2, K); 195 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 196 PPC_MUL(r_scratch1, r_scratch2, r_scratch1); 197 PPC_SUB(r_A, r_A, r_scratch1); 198 break; 199 case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */ 200 if (K == 1) 201 break; 202 PPC_LI32(r_scratch1, K); 203 PPC_DIVWU(r_A, r_A, r_scratch1); 204 break; 205 case BPF_ALU | BPF_AND | BPF_X: 206 ctx->seen |= SEEN_XREG; 207 PPC_AND(r_A, r_A, r_X); 208 break; 209 case BPF_ALU | BPF_AND | BPF_K: 210 if (!IMM_H(K)) 211 PPC_ANDI(r_A, r_A, K); 212 else { 213 PPC_LI32(r_scratch1, K); 214 PPC_AND(r_A, r_A, r_scratch1); 215 } 216 break; 217 case BPF_ALU | BPF_OR | BPF_X: 218 ctx->seen |= SEEN_XREG; 219 PPC_OR(r_A, r_A, r_X); 220 break; 221 case BPF_ALU | BPF_OR | BPF_K: 222 if (IMM_L(K)) 223 PPC_ORI(r_A, r_A, IMM_L(K)); 224 if (K >= 65536) 225 PPC_ORIS(r_A, r_A, IMM_H(K)); 226 break; 227 case BPF_ANC | SKF_AD_ALU_XOR_X: 228 case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */ 229 ctx->seen |= SEEN_XREG; 230 PPC_XOR(r_A, r_A, r_X); 231 break; 232 case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */ 233 if (IMM_L(K)) 234 PPC_XORI(r_A, r_A, IMM_L(K)); 235 if (K >= 65536) 236 PPC_XORIS(r_A, r_A, IMM_H(K)); 237 break; 238 case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */ 239 ctx->seen |= SEEN_XREG; 240 PPC_SLW(r_A, r_A, r_X); 241 break; 242 case BPF_ALU | BPF_LSH | BPF_K: 243 if (K == 0) 244 break; 245 else 246 PPC_SLWI(r_A, r_A, K); 247 break; 248 case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */ 249 ctx->seen |= SEEN_XREG; 250 PPC_SRW(r_A, r_A, r_X); 251 break; 252 case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */ 253 if (K == 0) 254 break; 255 else 256 PPC_SRWI(r_A, r_A, K); 257 break; 258 case BPF_ALU | BPF_NEG: 259 PPC_NEG(r_A, r_A); 260 break; 261 case BPF_RET | BPF_K: 262 PPC_LI32(r_ret, K); 263 if (!K) { 264 if (ctx->pc_ret0 == -1) 265 ctx->pc_ret0 = i; 266 } 267 /* 268 * If this isn't the very last instruction, branch to 269 * the epilogue if we've stuff to clean up. Otherwise, 270 * if there's nothing to tidy, just return. If we /are/ 271 * the last instruction, we're about to fall through to 272 * the epilogue to return. 273 */ 274 if (i != flen - 1) { 275 /* 276 * Note: 'seen' is properly valid only on pass 277 * #2. Both parts of this conditional are the 278 * same instruction size though, meaning the 279 * first pass will still correctly determine the 280 * code size/addresses. 281 */ 282 if (ctx->seen) 283 PPC_JMP(exit_addr); 284 else 285 PPC_BLR(); 286 } 287 break; 288 case BPF_RET | BPF_A: 289 PPC_MR(r_ret, r_A); 290 if (i != flen - 1) { 291 if (ctx->seen) 292 PPC_JMP(exit_addr); 293 else 294 PPC_BLR(); 295 } 296 break; 297 case BPF_MISC | BPF_TAX: /* X = A */ 298 PPC_MR(r_X, r_A); 299 break; 300 case BPF_MISC | BPF_TXA: /* A = X */ 301 ctx->seen |= SEEN_XREG; 302 PPC_MR(r_A, r_X); 303 break; 304 305 /*** Constant loads/M[] access ***/ 306 case BPF_LD | BPF_IMM: /* A = K */ 307 PPC_LI32(r_A, K); 308 break; 309 case BPF_LDX | BPF_IMM: /* X = K */ 310 PPC_LI32(r_X, K); 311 break; 312 case BPF_LD | BPF_MEM: /* A = mem[K] */ 313 PPC_MR(r_A, r_M + (K & 0xf)); 314 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 315 break; 316 case BPF_LDX | BPF_MEM: /* X = mem[K] */ 317 PPC_MR(r_X, r_M + (K & 0xf)); 318 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 319 break; 320 case BPF_ST: /* mem[K] = A */ 321 PPC_MR(r_M + (K & 0xf), r_A); 322 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 323 break; 324 case BPF_STX: /* mem[K] = X */ 325 PPC_MR(r_M + (K & 0xf), r_X); 326 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 327 break; 328 case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */ 329 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 330 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 331 break; 332 case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */ 333 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 334 break; 335 336 /*** Ancillary info loads ***/ 337 case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */ 338 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 339 protocol) != 2); 340 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 341 protocol)); 342 break; 343 case BPF_ANC | SKF_AD_IFINDEX: 344 case BPF_ANC | SKF_AD_HATYPE: 345 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 346 ifindex) != 4); 347 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 348 type) != 2); 349 PPC_LL_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 350 dev)); 351 PPC_CMPDI(r_scratch1, 0); 352 if (ctx->pc_ret0 != -1) { 353 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 354 } else { 355 /* Exit, returning 0; first pass hits here. */ 356 PPC_BCC_SHORT(COND_NE, ctx->idx * 4 + 12); 357 PPC_LI(r_ret, 0); 358 PPC_JMP(exit_addr); 359 } 360 if (code == (BPF_ANC | SKF_AD_IFINDEX)) { 361 PPC_LWZ_OFFS(r_A, r_scratch1, 362 offsetof(struct net_device, ifindex)); 363 } else { 364 PPC_LHZ_OFFS(r_A, r_scratch1, 365 offsetof(struct net_device, type)); 366 } 367 368 break; 369 case BPF_ANC | SKF_AD_MARK: 370 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 371 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 372 mark)); 373 break; 374 case BPF_ANC | SKF_AD_RXHASH: 375 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 376 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 377 hash)); 378 break; 379 case BPF_ANC | SKF_AD_VLAN_TAG: 380 case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT: 381 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 382 BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000); 383 384 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 385 vlan_tci)); 386 if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) { 387 PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT); 388 } else { 389 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT); 390 PPC_SRWI(r_A, r_A, 12); 391 } 392 break; 393 case BPF_ANC | SKF_AD_QUEUE: 394 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 395 queue_mapping) != 2); 396 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 397 queue_mapping)); 398 break; 399 case BPF_ANC | SKF_AD_PKTTYPE: 400 PPC_LBZ_OFFS(r_A, r_skb, PKT_TYPE_OFFSET()); 401 PPC_ANDI(r_A, r_A, PKT_TYPE_MAX); 402 PPC_SRWI(r_A, r_A, 5); 403 break; 404 case BPF_ANC | SKF_AD_CPU: 405 PPC_BPF_LOAD_CPU(r_A); 406 break; 407 /*** Absolute loads from packet header/data ***/ 408 case BPF_LD | BPF_W | BPF_ABS: 409 func = CHOOSE_LOAD_FUNC(K, sk_load_word); 410 goto common_load; 411 case BPF_LD | BPF_H | BPF_ABS: 412 func = CHOOSE_LOAD_FUNC(K, sk_load_half); 413 goto common_load; 414 case BPF_LD | BPF_B | BPF_ABS: 415 func = CHOOSE_LOAD_FUNC(K, sk_load_byte); 416 common_load: 417 /* Load from [K]. */ 418 ctx->seen |= SEEN_DATAREF; 419 PPC_FUNC_ADDR(r_scratch1, func); 420 PPC_MTLR(r_scratch1); 421 PPC_LI32(r_addr, K); 422 PPC_BLRL(); 423 /* 424 * Helper returns 'lt' condition on error, and an 425 * appropriate return value in r3 426 */ 427 PPC_BCC(COND_LT, exit_addr); 428 break; 429 430 /*** Indirect loads from packet header/data ***/ 431 case BPF_LD | BPF_W | BPF_IND: 432 func = sk_load_word; 433 goto common_load_ind; 434 case BPF_LD | BPF_H | BPF_IND: 435 func = sk_load_half; 436 goto common_load_ind; 437 case BPF_LD | BPF_B | BPF_IND: 438 func = sk_load_byte; 439 common_load_ind: 440 /* 441 * Load from [X + K]. Negative offsets are tested for 442 * in the helper functions. 443 */ 444 ctx->seen |= SEEN_DATAREF | SEEN_XREG; 445 PPC_FUNC_ADDR(r_scratch1, func); 446 PPC_MTLR(r_scratch1); 447 PPC_ADDI(r_addr, r_X, IMM_L(K)); 448 if (K >= 32768) 449 PPC_ADDIS(r_addr, r_addr, IMM_HA(K)); 450 PPC_BLRL(); 451 /* If error, cr0.LT set */ 452 PPC_BCC(COND_LT, exit_addr); 453 break; 454 455 case BPF_LDX | BPF_B | BPF_MSH: 456 func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh); 457 goto common_load; 458 break; 459 460 /*** Jump and branches ***/ 461 case BPF_JMP | BPF_JA: 462 if (K != 0) 463 PPC_JMP(addrs[i + 1 + K]); 464 break; 465 466 case BPF_JMP | BPF_JGT | BPF_K: 467 case BPF_JMP | BPF_JGT | BPF_X: 468 true_cond = COND_GT; 469 goto cond_branch; 470 case BPF_JMP | BPF_JGE | BPF_K: 471 case BPF_JMP | BPF_JGE | BPF_X: 472 true_cond = COND_GE; 473 goto cond_branch; 474 case BPF_JMP | BPF_JEQ | BPF_K: 475 case BPF_JMP | BPF_JEQ | BPF_X: 476 true_cond = COND_EQ; 477 goto cond_branch; 478 case BPF_JMP | BPF_JSET | BPF_K: 479 case BPF_JMP | BPF_JSET | BPF_X: 480 true_cond = COND_NE; 481 /* Fall through */ 482 cond_branch: 483 /* same targets, can avoid doing the test :) */ 484 if (filter[i].jt == filter[i].jf) { 485 if (filter[i].jt > 0) 486 PPC_JMP(addrs[i + 1 + filter[i].jt]); 487 break; 488 } 489 490 switch (code) { 491 case BPF_JMP | BPF_JGT | BPF_X: 492 case BPF_JMP | BPF_JGE | BPF_X: 493 case BPF_JMP | BPF_JEQ | BPF_X: 494 ctx->seen |= SEEN_XREG; 495 PPC_CMPLW(r_A, r_X); 496 break; 497 case BPF_JMP | BPF_JSET | BPF_X: 498 ctx->seen |= SEEN_XREG; 499 PPC_AND_DOT(r_scratch1, r_A, r_X); 500 break; 501 case BPF_JMP | BPF_JEQ | BPF_K: 502 case BPF_JMP | BPF_JGT | BPF_K: 503 case BPF_JMP | BPF_JGE | BPF_K: 504 if (K < 32768) 505 PPC_CMPLWI(r_A, K); 506 else { 507 PPC_LI32(r_scratch1, K); 508 PPC_CMPLW(r_A, r_scratch1); 509 } 510 break; 511 case BPF_JMP | BPF_JSET | BPF_K: 512 if (K < 32768) 513 /* PPC_ANDI is /only/ dot-form */ 514 PPC_ANDI(r_scratch1, r_A, K); 515 else { 516 PPC_LI32(r_scratch1, K); 517 PPC_AND_DOT(r_scratch1, r_A, 518 r_scratch1); 519 } 520 break; 521 } 522 /* Sometimes branches are constructed "backward", with 523 * the false path being the branch and true path being 524 * a fallthrough to the next instruction. 525 */ 526 if (filter[i].jt == 0) 527 /* Swap the sense of the branch */ 528 PPC_BCC(true_cond ^ COND_CMP_TRUE, 529 addrs[i + 1 + filter[i].jf]); 530 else { 531 PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]); 532 if (filter[i].jf != 0) 533 PPC_JMP(addrs[i + 1 + filter[i].jf]); 534 } 535 break; 536 default: 537 /* The filter contains something cruel & unusual. 538 * We don't handle it, but also there shouldn't be 539 * anything missing from our list. 540 */ 541 if (printk_ratelimit()) 542 pr_err("BPF filter opcode %04x (@%d) unsupported\n", 543 filter[i].code, i); 544 return -ENOTSUPP; 545 } 546 547 } 548 /* Set end-of-body-code address for exit. */ 549 addrs[i] = ctx->idx * 4; 550 551 return 0; 552 } 553 554 void bpf_jit_compile(struct bpf_prog *fp) 555 { 556 unsigned int proglen; 557 unsigned int alloclen; 558 u32 *image = NULL; 559 u32 *code_base; 560 unsigned int *addrs; 561 struct codegen_context cgctx; 562 int pass; 563 int flen = fp->len; 564 565 if (!bpf_jit_enable) 566 return; 567 568 addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL); 569 if (addrs == NULL) 570 return; 571 572 /* 573 * There are multiple assembly passes as the generated code will change 574 * size as it settles down, figuring out the max branch offsets/exit 575 * paths required. 576 * 577 * The range of standard conditional branches is +/- 32Kbytes. Since 578 * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to 579 * finish with 8 bytes/instruction. Not feasible, so long jumps are 580 * used, distinct from short branches. 581 * 582 * Current: 583 * 584 * For now, both branch types assemble to 2 words (short branches padded 585 * with a NOP); this is less efficient, but assembly will always complete 586 * after exactly 3 passes: 587 * 588 * First pass: No code buffer; Program is "faux-generated" -- no code 589 * emitted but maximum size of output determined (and addrs[] filled 590 * in). Also, we note whether we use M[], whether we use skb data, etc. 591 * All generation choices assumed to be 'worst-case', e.g. branches all 592 * far (2 instructions), return path code reduction not available, etc. 593 * 594 * Second pass: Code buffer allocated with size determined previously. 595 * Prologue generated to support features we have seen used. Exit paths 596 * determined and addrs[] is filled in again, as code may be slightly 597 * smaller as a result. 598 * 599 * Third pass: Code generated 'for real', and branch destinations 600 * determined from now-accurate addrs[] map. 601 * 602 * Ideal: 603 * 604 * If we optimise this, near branches will be shorter. On the 605 * first assembly pass, we should err on the side of caution and 606 * generate the biggest code. On subsequent passes, branches will be 607 * generated short or long and code size will reduce. With smaller 608 * code, more branches may fall into the short category, and code will 609 * reduce more. 610 * 611 * Finally, if we see one pass generate code the same size as the 612 * previous pass we have converged and should now generate code for 613 * real. Allocating at the end will also save the memory that would 614 * otherwise be wasted by the (small) current code shrinkage. 615 * Preferably, we should do a small number of passes (e.g. 5) and if we 616 * haven't converged by then, get impatient and force code to generate 617 * as-is, even if the odd branch would be left long. The chances of a 618 * long jump are tiny with all but the most enormous of BPF filter 619 * inputs, so we should usually converge on the third pass. 620 */ 621 622 cgctx.idx = 0; 623 cgctx.seen = 0; 624 cgctx.pc_ret0 = -1; 625 /* Scouting faux-generate pass 0 */ 626 if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) 627 /* We hit something illegal or unsupported. */ 628 goto out; 629 630 /* 631 * Pretend to build prologue, given the features we've seen. This will 632 * update ctgtx.idx as it pretends to output instructions, then we can 633 * calculate total size from idx. 634 */ 635 bpf_jit_build_prologue(fp, 0, &cgctx); 636 bpf_jit_build_epilogue(0, &cgctx); 637 638 proglen = cgctx.idx * 4; 639 alloclen = proglen + FUNCTION_DESCR_SIZE; 640 image = module_alloc(alloclen); 641 if (!image) 642 goto out; 643 644 code_base = image + (FUNCTION_DESCR_SIZE/4); 645 646 /* Code generation passes 1-2 */ 647 for (pass = 1; pass < 3; pass++) { 648 /* Now build the prologue, body code & epilogue for real. */ 649 cgctx.idx = 0; 650 bpf_jit_build_prologue(fp, code_base, &cgctx); 651 bpf_jit_build_body(fp, code_base, &cgctx, addrs); 652 bpf_jit_build_epilogue(code_base, &cgctx); 653 654 if (bpf_jit_enable > 1) 655 pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, 656 proglen - (cgctx.idx * 4), cgctx.seen); 657 } 658 659 if (bpf_jit_enable > 1) 660 /* Note that we output the base address of the code_base 661 * rather than image, since opcodes are in code_base. 662 */ 663 bpf_jit_dump(flen, proglen, pass, code_base); 664 665 if (image) { 666 bpf_flush_icache(code_base, code_base + (proglen/4)); 667 #ifdef CONFIG_PPC64 668 /* Function descriptor nastiness: Address + TOC */ 669 ((u64 *)image)[0] = (u64)code_base; 670 ((u64 *)image)[1] = local_paca->kernel_toc; 671 #endif 672 fp->bpf_func = (void *)image; 673 fp->jited = 1; 674 } 675 out: 676 kfree(addrs); 677 return; 678 } 679 680 void bpf_jit_free(struct bpf_prog *fp) 681 { 682 if (fp->jited) 683 module_memfree(fp->bpf_func); 684 685 bpf_prog_unlock_free(fp); 686 } 687