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_jit32.h" 20 21 static inline void bpf_flush_icache(void *start, void *end) 22 { 23 smp_wmb(); 24 flush_icache_range((unsigned long)start, (unsigned long)end); 25 } 26 27 static void bpf_jit_build_prologue(struct bpf_prog *fp, u32 *image, 28 struct codegen_context *ctx) 29 { 30 int i; 31 const struct sock_filter *filter = fp->insns; 32 33 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 34 /* Make stackframe */ 35 if (ctx->seen & SEEN_DATAREF) { 36 /* If we call any helpers (for loads), save LR */ 37 EMIT(PPC_INST_MFLR | __PPC_RT(R0)); 38 PPC_BPF_STL(0, 1, PPC_LR_STKOFF); 39 40 /* Back up non-volatile regs. */ 41 PPC_BPF_STL(r_D, 1, -(REG_SZ*(32-r_D))); 42 PPC_BPF_STL(r_HL, 1, -(REG_SZ*(32-r_HL))); 43 } 44 if (ctx->seen & SEEN_MEM) { 45 /* 46 * Conditionally save regs r15-r31 as some will be used 47 * for M[] data. 48 */ 49 for (i = r_M; i < (r_M+16); i++) { 50 if (ctx->seen & (1 << (i-r_M))) 51 PPC_BPF_STL(i, 1, -(REG_SZ*(32-i))); 52 } 53 } 54 PPC_BPF_STLU(1, 1, -BPF_PPC_STACKFRAME); 55 } 56 57 if (ctx->seen & SEEN_DATAREF) { 58 /* 59 * If this filter needs to access skb data, 60 * prepare r_D and r_HL: 61 * r_HL = skb->len - skb->data_len 62 * r_D = skb->data 63 */ 64 PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 65 data_len)); 66 PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len)); 67 PPC_SUB(r_HL, r_HL, r_scratch1); 68 PPC_LL_OFFS(r_D, r_skb, offsetof(struct sk_buff, data)); 69 } 70 71 if (ctx->seen & SEEN_XREG) { 72 /* 73 * TODO: Could also detect whether first instr. sets X and 74 * avoid this (as below, with A). 75 */ 76 PPC_LI(r_X, 0); 77 } 78 79 /* make sure we dont leak kernel information to user */ 80 if (bpf_needs_clear_a(&filter[0])) 81 PPC_LI(r_A, 0); 82 } 83 84 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) 85 { 86 int i; 87 88 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 89 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME); 90 if (ctx->seen & SEEN_DATAREF) { 91 PPC_BPF_LL(0, 1, PPC_LR_STKOFF); 92 PPC_MTLR(0); 93 PPC_BPF_LL(r_D, 1, -(REG_SZ*(32-r_D))); 94 PPC_BPF_LL(r_HL, 1, -(REG_SZ*(32-r_HL))); 95 } 96 if (ctx->seen & SEEN_MEM) { 97 /* Restore any saved non-vol registers */ 98 for (i = r_M; i < (r_M+16); i++) { 99 if (ctx->seen & (1 << (i-r_M))) 100 PPC_BPF_LL(i, 1, -(REG_SZ*(32-i))); 101 } 102 } 103 } 104 /* The RETs have left a return value in R3. */ 105 106 PPC_BLR(); 107 } 108 109 #define CHOOSE_LOAD_FUNC(K, func) \ 110 ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset) 111 112 /* Assemble the body code between the prologue & epilogue. */ 113 static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 114 struct codegen_context *ctx, 115 unsigned int *addrs) 116 { 117 const struct sock_filter *filter = fp->insns; 118 int flen = fp->len; 119 u8 *func; 120 unsigned int true_cond; 121 int i; 122 123 /* Start of epilogue code */ 124 unsigned int exit_addr = addrs[flen]; 125 126 for (i = 0; i < flen; i++) { 127 unsigned int K = filter[i].k; 128 u16 code = bpf_anc_helper(&filter[i]); 129 130 /* 131 * addrs[] maps a BPF bytecode address into a real offset from 132 * the start of the body code. 133 */ 134 addrs[i] = ctx->idx * 4; 135 136 switch (code) { 137 /*** ALU ops ***/ 138 case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */ 139 ctx->seen |= SEEN_XREG; 140 PPC_ADD(r_A, r_A, r_X); 141 break; 142 case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */ 143 if (!K) 144 break; 145 PPC_ADDI(r_A, r_A, IMM_L(K)); 146 if (K >= 32768) 147 PPC_ADDIS(r_A, r_A, IMM_HA(K)); 148 break; 149 case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */ 150 ctx->seen |= SEEN_XREG; 151 PPC_SUB(r_A, r_A, r_X); 152 break; 153 case BPF_ALU | BPF_SUB | 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_MUL | BPF_X: /* A *= X; */ 161 ctx->seen |= SEEN_XREG; 162 PPC_MULW(r_A, r_A, r_X); 163 break; 164 case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */ 165 if (K < 32768) 166 PPC_MULI(r_A, r_A, K); 167 else { 168 PPC_LI32(r_scratch1, K); 169 PPC_MULW(r_A, r_A, r_scratch1); 170 } 171 break; 172 case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */ 173 case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */ 174 ctx->seen |= SEEN_XREG; 175 PPC_CMPWI(r_X, 0); 176 if (ctx->pc_ret0 != -1) { 177 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 178 } else { 179 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 180 PPC_LI(r_ret, 0); 181 PPC_JMP(exit_addr); 182 } 183 if (code == (BPF_ALU | BPF_MOD | BPF_X)) { 184 PPC_DIVWU(r_scratch1, r_A, r_X); 185 PPC_MULW(r_scratch1, r_X, r_scratch1); 186 PPC_SUB(r_A, r_A, r_scratch1); 187 } else { 188 PPC_DIVWU(r_A, r_A, r_X); 189 } 190 break; 191 case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */ 192 PPC_LI32(r_scratch2, K); 193 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 194 PPC_MULW(r_scratch1, r_scratch2, r_scratch1); 195 PPC_SUB(r_A, r_A, r_scratch1); 196 break; 197 case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */ 198 if (K == 1) 199 break; 200 PPC_LI32(r_scratch1, K); 201 PPC_DIVWU(r_A, r_A, r_scratch1); 202 break; 203 case BPF_ALU | BPF_AND | BPF_X: 204 ctx->seen |= SEEN_XREG; 205 PPC_AND(r_A, r_A, r_X); 206 break; 207 case BPF_ALU | BPF_AND | BPF_K: 208 if (!IMM_H(K)) 209 PPC_ANDI(r_A, r_A, K); 210 else { 211 PPC_LI32(r_scratch1, K); 212 PPC_AND(r_A, r_A, r_scratch1); 213 } 214 break; 215 case BPF_ALU | BPF_OR | BPF_X: 216 ctx->seen |= SEEN_XREG; 217 PPC_OR(r_A, r_A, r_X); 218 break; 219 case BPF_ALU | BPF_OR | BPF_K: 220 if (IMM_L(K)) 221 PPC_ORI(r_A, r_A, IMM_L(K)); 222 if (K >= 65536) 223 PPC_ORIS(r_A, r_A, IMM_H(K)); 224 break; 225 case BPF_ANC | SKF_AD_ALU_XOR_X: 226 case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */ 227 ctx->seen |= SEEN_XREG; 228 PPC_XOR(r_A, r_A, r_X); 229 break; 230 case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */ 231 if (IMM_L(K)) 232 PPC_XORI(r_A, r_A, IMM_L(K)); 233 if (K >= 65536) 234 PPC_XORIS(r_A, r_A, IMM_H(K)); 235 break; 236 case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */ 237 ctx->seen |= SEEN_XREG; 238 PPC_SLW(r_A, r_A, r_X); 239 break; 240 case BPF_ALU | BPF_LSH | BPF_K: 241 if (K == 0) 242 break; 243 else 244 PPC_SLWI(r_A, r_A, K); 245 break; 246 case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */ 247 ctx->seen |= SEEN_XREG; 248 PPC_SRW(r_A, r_A, r_X); 249 break; 250 case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */ 251 if (K == 0) 252 break; 253 else 254 PPC_SRWI(r_A, r_A, K); 255 break; 256 case BPF_ALU | BPF_NEG: 257 PPC_NEG(r_A, r_A); 258 break; 259 case BPF_RET | BPF_K: 260 PPC_LI32(r_ret, K); 261 if (!K) { 262 if (ctx->pc_ret0 == -1) 263 ctx->pc_ret0 = i; 264 } 265 /* 266 * If this isn't the very last instruction, branch to 267 * the epilogue if we've stuff to clean up. Otherwise, 268 * if there's nothing to tidy, just return. If we /are/ 269 * the last instruction, we're about to fall through to 270 * the epilogue to return. 271 */ 272 if (i != flen - 1) { 273 /* 274 * Note: 'seen' is properly valid only on pass 275 * #2. Both parts of this conditional are the 276 * same instruction size though, meaning the 277 * first pass will still correctly determine the 278 * code size/addresses. 279 */ 280 if (ctx->seen) 281 PPC_JMP(exit_addr); 282 else 283 PPC_BLR(); 284 } 285 break; 286 case BPF_RET | BPF_A: 287 PPC_MR(r_ret, r_A); 288 if (i != flen - 1) { 289 if (ctx->seen) 290 PPC_JMP(exit_addr); 291 else 292 PPC_BLR(); 293 } 294 break; 295 case BPF_MISC | BPF_TAX: /* X = A */ 296 PPC_MR(r_X, r_A); 297 break; 298 case BPF_MISC | BPF_TXA: /* A = X */ 299 ctx->seen |= SEEN_XREG; 300 PPC_MR(r_A, r_X); 301 break; 302 303 /*** Constant loads/M[] access ***/ 304 case BPF_LD | BPF_IMM: /* A = K */ 305 PPC_LI32(r_A, K); 306 break; 307 case BPF_LDX | BPF_IMM: /* X = K */ 308 PPC_LI32(r_X, K); 309 break; 310 case BPF_LD | BPF_MEM: /* A = mem[K] */ 311 PPC_MR(r_A, r_M + (K & 0xf)); 312 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 313 break; 314 case BPF_LDX | BPF_MEM: /* X = mem[K] */ 315 PPC_MR(r_X, r_M + (K & 0xf)); 316 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 317 break; 318 case BPF_ST: /* mem[K] = A */ 319 PPC_MR(r_M + (K & 0xf), r_A); 320 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 321 break; 322 case BPF_STX: /* mem[K] = X */ 323 PPC_MR(r_M + (K & 0xf), r_X); 324 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 325 break; 326 case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */ 327 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 328 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 329 break; 330 case BPF_LDX | BPF_W | BPF_ABS: /* A = *((u32 *)(seccomp_data + K)); */ 331 PPC_LWZ_OFFS(r_A, r_skb, K); 332 break; 333 case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */ 334 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 335 break; 336 337 /*** Ancillary info loads ***/ 338 case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */ 339 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 340 protocol) != 2); 341 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 342 protocol)); 343 break; 344 case BPF_ANC | SKF_AD_IFINDEX: 345 case BPF_ANC | SKF_AD_HATYPE: 346 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 347 ifindex) != 4); 348 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 349 type) != 2); 350 PPC_LL_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 351 dev)); 352 PPC_CMPDI(r_scratch1, 0); 353 if (ctx->pc_ret0 != -1) { 354 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 355 } else { 356 /* Exit, returning 0; first pass hits here. */ 357 PPC_BCC_SHORT(COND_NE, ctx->idx * 4 + 12); 358 PPC_LI(r_ret, 0); 359 PPC_JMP(exit_addr); 360 } 361 if (code == (BPF_ANC | SKF_AD_IFINDEX)) { 362 PPC_LWZ_OFFS(r_A, r_scratch1, 363 offsetof(struct net_device, ifindex)); 364 } else { 365 PPC_LHZ_OFFS(r_A, r_scratch1, 366 offsetof(struct net_device, type)); 367 } 368 369 break; 370 case BPF_ANC | SKF_AD_MARK: 371 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 372 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 373 mark)); 374 break; 375 case BPF_ANC | SKF_AD_RXHASH: 376 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 377 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 378 hash)); 379 break; 380 case BPF_ANC | SKF_AD_VLAN_TAG: 381 case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT: 382 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 383 BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000); 384 385 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 386 vlan_tci)); 387 if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) { 388 PPC_ANDI(r_A, r_A, ~VLAN_TAG_PRESENT); 389 } else { 390 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT); 391 PPC_SRWI(r_A, r_A, 12); 392 } 393 break; 394 case BPF_ANC | SKF_AD_QUEUE: 395 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 396 queue_mapping) != 2); 397 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 398 queue_mapping)); 399 break; 400 case BPF_ANC | SKF_AD_PKTTYPE: 401 PPC_LBZ_OFFS(r_A, r_skb, PKT_TYPE_OFFSET()); 402 PPC_ANDI(r_A, r_A, PKT_TYPE_MAX); 403 PPC_SRWI(r_A, r_A, 5); 404 break; 405 case BPF_ANC | SKF_AD_CPU: 406 PPC_BPF_LOAD_CPU(r_A); 407 break; 408 /*** Absolute loads from packet header/data ***/ 409 case BPF_LD | BPF_W | BPF_ABS: 410 func = CHOOSE_LOAD_FUNC(K, sk_load_word); 411 goto common_load; 412 case BPF_LD | BPF_H | BPF_ABS: 413 func = CHOOSE_LOAD_FUNC(K, sk_load_half); 414 goto common_load; 415 case BPF_LD | BPF_B | BPF_ABS: 416 func = CHOOSE_LOAD_FUNC(K, sk_load_byte); 417 common_load: 418 /* Load from [K]. */ 419 ctx->seen |= SEEN_DATAREF; 420 PPC_FUNC_ADDR(r_scratch1, func); 421 PPC_MTLR(r_scratch1); 422 PPC_LI32(r_addr, K); 423 PPC_BLRL(); 424 /* 425 * Helper returns 'lt' condition on error, and an 426 * appropriate return value in r3 427 */ 428 PPC_BCC(COND_LT, exit_addr); 429 break; 430 431 /*** Indirect loads from packet header/data ***/ 432 case BPF_LD | BPF_W | BPF_IND: 433 func = sk_load_word; 434 goto common_load_ind; 435 case BPF_LD | BPF_H | BPF_IND: 436 func = sk_load_half; 437 goto common_load_ind; 438 case BPF_LD | BPF_B | BPF_IND: 439 func = sk_load_byte; 440 common_load_ind: 441 /* 442 * Load from [X + K]. Negative offsets are tested for 443 * in the helper functions. 444 */ 445 ctx->seen |= SEEN_DATAREF | SEEN_XREG; 446 PPC_FUNC_ADDR(r_scratch1, func); 447 PPC_MTLR(r_scratch1); 448 PPC_ADDI(r_addr, r_X, IMM_L(K)); 449 if (K >= 32768) 450 PPC_ADDIS(r_addr, r_addr, IMM_HA(K)); 451 PPC_BLRL(); 452 /* If error, cr0.LT set */ 453 PPC_BCC(COND_LT, exit_addr); 454 break; 455 456 case BPF_LDX | BPF_B | BPF_MSH: 457 func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh); 458 goto common_load; 459 break; 460 461 /*** Jump and branches ***/ 462 case BPF_JMP | BPF_JA: 463 if (K != 0) 464 PPC_JMP(addrs[i + 1 + K]); 465 break; 466 467 case BPF_JMP | BPF_JGT | BPF_K: 468 case BPF_JMP | BPF_JGT | BPF_X: 469 true_cond = COND_GT; 470 goto cond_branch; 471 case BPF_JMP | BPF_JGE | BPF_K: 472 case BPF_JMP | BPF_JGE | BPF_X: 473 true_cond = COND_GE; 474 goto cond_branch; 475 case BPF_JMP | BPF_JEQ | BPF_K: 476 case BPF_JMP | BPF_JEQ | BPF_X: 477 true_cond = COND_EQ; 478 goto cond_branch; 479 case BPF_JMP | BPF_JSET | BPF_K: 480 case BPF_JMP | BPF_JSET | BPF_X: 481 true_cond = COND_NE; 482 /* Fall through */ 483 cond_branch: 484 /* same targets, can avoid doing the test :) */ 485 if (filter[i].jt == filter[i].jf) { 486 if (filter[i].jt > 0) 487 PPC_JMP(addrs[i + 1 + filter[i].jt]); 488 break; 489 } 490 491 switch (code) { 492 case BPF_JMP | BPF_JGT | BPF_X: 493 case BPF_JMP | BPF_JGE | BPF_X: 494 case BPF_JMP | BPF_JEQ | BPF_X: 495 ctx->seen |= SEEN_XREG; 496 PPC_CMPLW(r_A, r_X); 497 break; 498 case BPF_JMP | BPF_JSET | BPF_X: 499 ctx->seen |= SEEN_XREG; 500 PPC_AND_DOT(r_scratch1, r_A, r_X); 501 break; 502 case BPF_JMP | BPF_JEQ | BPF_K: 503 case BPF_JMP | BPF_JGT | BPF_K: 504 case BPF_JMP | BPF_JGE | BPF_K: 505 if (K < 32768) 506 PPC_CMPLWI(r_A, K); 507 else { 508 PPC_LI32(r_scratch1, K); 509 PPC_CMPLW(r_A, r_scratch1); 510 } 511 break; 512 case BPF_JMP | BPF_JSET | BPF_K: 513 if (K < 32768) 514 /* PPC_ANDI is /only/ dot-form */ 515 PPC_ANDI(r_scratch1, r_A, K); 516 else { 517 PPC_LI32(r_scratch1, K); 518 PPC_AND_DOT(r_scratch1, r_A, 519 r_scratch1); 520 } 521 break; 522 } 523 /* Sometimes branches are constructed "backward", with 524 * the false path being the branch and true path being 525 * a fallthrough to the next instruction. 526 */ 527 if (filter[i].jt == 0) 528 /* Swap the sense of the branch */ 529 PPC_BCC(true_cond ^ COND_CMP_TRUE, 530 addrs[i + 1 + filter[i].jf]); 531 else { 532 PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]); 533 if (filter[i].jf != 0) 534 PPC_JMP(addrs[i + 1 + filter[i].jf]); 535 } 536 break; 537 default: 538 /* The filter contains something cruel & unusual. 539 * We don't handle it, but also there shouldn't be 540 * anything missing from our list. 541 */ 542 if (printk_ratelimit()) 543 pr_err("BPF filter opcode %04x (@%d) unsupported\n", 544 filter[i].code, i); 545 return -ENOTSUPP; 546 } 547 548 } 549 /* Set end-of-body-code address for exit. */ 550 addrs[i] = ctx->idx * 4; 551 552 return 0; 553 } 554 555 void bpf_jit_compile(struct bpf_prog *fp) 556 { 557 unsigned int proglen; 558 unsigned int alloclen; 559 u32 *image = NULL; 560 u32 *code_base; 561 unsigned int *addrs; 562 struct codegen_context cgctx; 563 int pass; 564 int flen = fp->len; 565 566 if (!bpf_jit_enable) 567 return; 568 569 addrs = kcalloc(flen + 1, sizeof(*addrs), GFP_KERNEL); 570 if (addrs == NULL) 571 return; 572 573 /* 574 * There are multiple assembly passes as the generated code will change 575 * size as it settles down, figuring out the max branch offsets/exit 576 * paths required. 577 * 578 * The range of standard conditional branches is +/- 32Kbytes. Since 579 * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to 580 * finish with 8 bytes/instruction. Not feasible, so long jumps are 581 * used, distinct from short branches. 582 * 583 * Current: 584 * 585 * For now, both branch types assemble to 2 words (short branches padded 586 * with a NOP); this is less efficient, but assembly will always complete 587 * after exactly 3 passes: 588 * 589 * First pass: No code buffer; Program is "faux-generated" -- no code 590 * emitted but maximum size of output determined (and addrs[] filled 591 * in). Also, we note whether we use M[], whether we use skb data, etc. 592 * All generation choices assumed to be 'worst-case', e.g. branches all 593 * far (2 instructions), return path code reduction not available, etc. 594 * 595 * Second pass: Code buffer allocated with size determined previously. 596 * Prologue generated to support features we have seen used. Exit paths 597 * determined and addrs[] is filled in again, as code may be slightly 598 * smaller as a result. 599 * 600 * Third pass: Code generated 'for real', and branch destinations 601 * determined from now-accurate addrs[] map. 602 * 603 * Ideal: 604 * 605 * If we optimise this, near branches will be shorter. On the 606 * first assembly pass, we should err on the side of caution and 607 * generate the biggest code. On subsequent passes, branches will be 608 * generated short or long and code size will reduce. With smaller 609 * code, more branches may fall into the short category, and code will 610 * reduce more. 611 * 612 * Finally, if we see one pass generate code the same size as the 613 * previous pass we have converged and should now generate code for 614 * real. Allocating at the end will also save the memory that would 615 * otherwise be wasted by the (small) current code shrinkage. 616 * Preferably, we should do a small number of passes (e.g. 5) and if we 617 * haven't converged by then, get impatient and force code to generate 618 * as-is, even if the odd branch would be left long. The chances of a 619 * long jump are tiny with all but the most enormous of BPF filter 620 * inputs, so we should usually converge on the third pass. 621 */ 622 623 cgctx.idx = 0; 624 cgctx.seen = 0; 625 cgctx.pc_ret0 = -1; 626 /* Scouting faux-generate pass 0 */ 627 if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) 628 /* We hit something illegal or unsupported. */ 629 goto out; 630 631 /* 632 * Pretend to build prologue, given the features we've seen. This will 633 * update ctgtx.idx as it pretends to output instructions, then we can 634 * calculate total size from idx. 635 */ 636 bpf_jit_build_prologue(fp, 0, &cgctx); 637 bpf_jit_build_epilogue(0, &cgctx); 638 639 proglen = cgctx.idx * 4; 640 alloclen = proglen + FUNCTION_DESCR_SIZE; 641 image = module_alloc(alloclen); 642 if (!image) 643 goto out; 644 645 code_base = image + (FUNCTION_DESCR_SIZE/4); 646 647 /* Code generation passes 1-2 */ 648 for (pass = 1; pass < 3; pass++) { 649 /* Now build the prologue, body code & epilogue for real. */ 650 cgctx.idx = 0; 651 bpf_jit_build_prologue(fp, code_base, &cgctx); 652 bpf_jit_build_body(fp, code_base, &cgctx, addrs); 653 bpf_jit_build_epilogue(code_base, &cgctx); 654 655 if (bpf_jit_enable > 1) 656 pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, 657 proglen - (cgctx.idx * 4), cgctx.seen); 658 } 659 660 if (bpf_jit_enable > 1) 661 /* Note that we output the base address of the code_base 662 * rather than image, since opcodes are in code_base. 663 */ 664 bpf_jit_dump(flen, proglen, pass, code_base); 665 666 bpf_flush_icache(code_base, code_base + (proglen/4)); 667 668 #ifdef CONFIG_PPC64 669 /* Function descriptor nastiness: Address + TOC */ 670 ((u64 *)image)[0] = (u64)code_base; 671 ((u64 *)image)[1] = local_paca->kernel_toc; 672 #endif 673 674 fp->bpf_func = (void *)image; 675 fp->jited = 1; 676 677 out: 678 kfree(addrs); 679 return; 680 } 681 682 void bpf_jit_free(struct bpf_prog *fp) 683 { 684 if (fp->jited) 685 module_memfree(fp->bpf_func); 686 687 bpf_prog_unlock_free(fp); 688 } 689