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 <asm/asm-compat.h> 16 #include <linux/netdevice.h> 17 #include <linux/filter.h> 18 #include <linux/if_vlan.h> 19 20 #include "bpf_jit32.h" 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_BPF_STL(0, 1, PPC_LR_STKOFF); 40 41 /* Back up non-volatile regs. */ 42 PPC_BPF_STL(r_D, 1, -(REG_SZ*(32-r_D))); 43 PPC_BPF_STL(r_HL, 1, -(REG_SZ*(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_BPF_STL(i, 1, -(REG_SZ*(32-i))); 53 } 54 } 55 PPC_BPF_STLU(1, 1, -BPF_PPC_STACKFRAME); 56 } 57 58 if (ctx->seen & SEEN_DATAREF) { 59 /* 60 * If this filter needs to access skb data, 61 * prepare r_D and r_HL: 62 * r_HL = skb->len - skb->data_len 63 * r_D = skb->data 64 */ 65 PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 66 data_len)); 67 PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len)); 68 PPC_SUB(r_HL, r_HL, r_scratch1); 69 PPC_LL_OFFS(r_D, r_skb, offsetof(struct sk_buff, data)); 70 } 71 72 if (ctx->seen & SEEN_XREG) { 73 /* 74 * TODO: Could also detect whether first instr. sets X and 75 * avoid this (as below, with A). 76 */ 77 PPC_LI(r_X, 0); 78 } 79 80 /* make sure we dont leak kernel information to user */ 81 if (bpf_needs_clear_a(&filter[0])) 82 PPC_LI(r_A, 0); 83 } 84 85 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) 86 { 87 int i; 88 89 if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) { 90 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME); 91 if (ctx->seen & SEEN_DATAREF) { 92 PPC_BPF_LL(0, 1, PPC_LR_STKOFF); 93 PPC_MTLR(0); 94 PPC_BPF_LL(r_D, 1, -(REG_SZ*(32-r_D))); 95 PPC_BPF_LL(r_HL, 1, -(REG_SZ*(32-r_HL))); 96 } 97 if (ctx->seen & SEEN_MEM) { 98 /* Restore any saved non-vol registers */ 99 for (i = r_M; i < (r_M+16); i++) { 100 if (ctx->seen & (1 << (i-r_M))) 101 PPC_BPF_LL(i, 1, -(REG_SZ*(32-i))); 102 } 103 } 104 } 105 /* The RETs have left a return value in R3. */ 106 107 PPC_BLR(); 108 } 109 110 #define CHOOSE_LOAD_FUNC(K, func) \ 111 ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset) 112 113 /* Assemble the body code between the prologue & epilogue. */ 114 static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, 115 struct codegen_context *ctx, 116 unsigned int *addrs) 117 { 118 const struct sock_filter *filter = fp->insns; 119 int flen = fp->len; 120 u8 *func; 121 unsigned int true_cond; 122 int i; 123 124 /* Start of epilogue code */ 125 unsigned int exit_addr = addrs[flen]; 126 127 for (i = 0; i < flen; i++) { 128 unsigned int K = filter[i].k; 129 u16 code = bpf_anc_helper(&filter[i]); 130 131 /* 132 * addrs[] maps a BPF bytecode address into a real offset from 133 * the start of the body code. 134 */ 135 addrs[i] = ctx->idx * 4; 136 137 switch (code) { 138 /*** ALU ops ***/ 139 case BPF_ALU | BPF_ADD | BPF_X: /* A += X; */ 140 ctx->seen |= SEEN_XREG; 141 PPC_ADD(r_A, r_A, r_X); 142 break; 143 case BPF_ALU | BPF_ADD | BPF_K: /* A += K; */ 144 if (!K) 145 break; 146 PPC_ADDI(r_A, r_A, IMM_L(K)); 147 if (K >= 32768) 148 PPC_ADDIS(r_A, r_A, IMM_HA(K)); 149 break; 150 case BPF_ALU | BPF_SUB | BPF_X: /* A -= X; */ 151 ctx->seen |= SEEN_XREG; 152 PPC_SUB(r_A, r_A, r_X); 153 break; 154 case BPF_ALU | BPF_SUB | BPF_K: /* A -= K */ 155 if (!K) 156 break; 157 PPC_ADDI(r_A, r_A, IMM_L(-K)); 158 if (K >= 32768) 159 PPC_ADDIS(r_A, r_A, IMM_HA(-K)); 160 break; 161 case BPF_ALU | BPF_MUL | BPF_X: /* A *= X; */ 162 ctx->seen |= SEEN_XREG; 163 PPC_MULW(r_A, r_A, r_X); 164 break; 165 case BPF_ALU | BPF_MUL | BPF_K: /* A *= K */ 166 if (K < 32768) 167 PPC_MULI(r_A, r_A, K); 168 else { 169 PPC_LI32(r_scratch1, K); 170 PPC_MULW(r_A, r_A, r_scratch1); 171 } 172 break; 173 case BPF_ALU | BPF_MOD | BPF_X: /* A %= X; */ 174 case BPF_ALU | BPF_DIV | BPF_X: /* A /= X; */ 175 ctx->seen |= SEEN_XREG; 176 PPC_CMPWI(r_X, 0); 177 if (ctx->pc_ret0 != -1) { 178 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 179 } else { 180 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12); 181 PPC_LI(r_ret, 0); 182 PPC_JMP(exit_addr); 183 } 184 if (code == (BPF_ALU | BPF_MOD | BPF_X)) { 185 PPC_DIVWU(r_scratch1, r_A, r_X); 186 PPC_MULW(r_scratch1, r_X, r_scratch1); 187 PPC_SUB(r_A, r_A, r_scratch1); 188 } else { 189 PPC_DIVWU(r_A, r_A, r_X); 190 } 191 break; 192 case BPF_ALU | BPF_MOD | BPF_K: /* A %= K; */ 193 PPC_LI32(r_scratch2, K); 194 PPC_DIVWU(r_scratch1, r_A, r_scratch2); 195 PPC_MULW(r_scratch1, r_scratch2, r_scratch1); 196 PPC_SUB(r_A, r_A, r_scratch1); 197 break; 198 case BPF_ALU | BPF_DIV | BPF_K: /* A /= K */ 199 if (K == 1) 200 break; 201 PPC_LI32(r_scratch1, K); 202 PPC_DIVWU(r_A, r_A, r_scratch1); 203 break; 204 case BPF_ALU | BPF_AND | BPF_X: 205 ctx->seen |= SEEN_XREG; 206 PPC_AND(r_A, r_A, r_X); 207 break; 208 case BPF_ALU | BPF_AND | BPF_K: 209 if (!IMM_H(K)) 210 PPC_ANDI(r_A, r_A, K); 211 else { 212 PPC_LI32(r_scratch1, K); 213 PPC_AND(r_A, r_A, r_scratch1); 214 } 215 break; 216 case BPF_ALU | BPF_OR | BPF_X: 217 ctx->seen |= SEEN_XREG; 218 PPC_OR(r_A, r_A, r_X); 219 break; 220 case BPF_ALU | BPF_OR | BPF_K: 221 if (IMM_L(K)) 222 PPC_ORI(r_A, r_A, IMM_L(K)); 223 if (K >= 65536) 224 PPC_ORIS(r_A, r_A, IMM_H(K)); 225 break; 226 case BPF_ANC | SKF_AD_ALU_XOR_X: 227 case BPF_ALU | BPF_XOR | BPF_X: /* A ^= X */ 228 ctx->seen |= SEEN_XREG; 229 PPC_XOR(r_A, r_A, r_X); 230 break; 231 case BPF_ALU | BPF_XOR | BPF_K: /* A ^= K */ 232 if (IMM_L(K)) 233 PPC_XORI(r_A, r_A, IMM_L(K)); 234 if (K >= 65536) 235 PPC_XORIS(r_A, r_A, IMM_H(K)); 236 break; 237 case BPF_ALU | BPF_LSH | BPF_X: /* A <<= X; */ 238 ctx->seen |= SEEN_XREG; 239 PPC_SLW(r_A, r_A, r_X); 240 break; 241 case BPF_ALU | BPF_LSH | BPF_K: 242 if (K == 0) 243 break; 244 else 245 PPC_SLWI(r_A, r_A, K); 246 break; 247 case BPF_ALU | BPF_RSH | BPF_X: /* A >>= X; */ 248 ctx->seen |= SEEN_XREG; 249 PPC_SRW(r_A, r_A, r_X); 250 break; 251 case BPF_ALU | BPF_RSH | BPF_K: /* A >>= K; */ 252 if (K == 0) 253 break; 254 else 255 PPC_SRWI(r_A, r_A, K); 256 break; 257 case BPF_ALU | BPF_NEG: 258 PPC_NEG(r_A, r_A); 259 break; 260 case BPF_RET | BPF_K: 261 PPC_LI32(r_ret, K); 262 if (!K) { 263 if (ctx->pc_ret0 == -1) 264 ctx->pc_ret0 = i; 265 } 266 /* 267 * If this isn't the very last instruction, branch to 268 * the epilogue if we've stuff to clean up. Otherwise, 269 * if there's nothing to tidy, just return. If we /are/ 270 * the last instruction, we're about to fall through to 271 * the epilogue to return. 272 */ 273 if (i != flen - 1) { 274 /* 275 * Note: 'seen' is properly valid only on pass 276 * #2. Both parts of this conditional are the 277 * same instruction size though, meaning the 278 * first pass will still correctly determine the 279 * code size/addresses. 280 */ 281 if (ctx->seen) 282 PPC_JMP(exit_addr); 283 else 284 PPC_BLR(); 285 } 286 break; 287 case BPF_RET | BPF_A: 288 PPC_MR(r_ret, r_A); 289 if (i != flen - 1) { 290 if (ctx->seen) 291 PPC_JMP(exit_addr); 292 else 293 PPC_BLR(); 294 } 295 break; 296 case BPF_MISC | BPF_TAX: /* X = A */ 297 PPC_MR(r_X, r_A); 298 break; 299 case BPF_MISC | BPF_TXA: /* A = X */ 300 ctx->seen |= SEEN_XREG; 301 PPC_MR(r_A, r_X); 302 break; 303 304 /*** Constant loads/M[] access ***/ 305 case BPF_LD | BPF_IMM: /* A = K */ 306 PPC_LI32(r_A, K); 307 break; 308 case BPF_LDX | BPF_IMM: /* X = K */ 309 PPC_LI32(r_X, K); 310 break; 311 case BPF_LD | BPF_MEM: /* A = mem[K] */ 312 PPC_MR(r_A, r_M + (K & 0xf)); 313 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 314 break; 315 case BPF_LDX | BPF_MEM: /* X = mem[K] */ 316 PPC_MR(r_X, r_M + (K & 0xf)); 317 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 318 break; 319 case BPF_ST: /* mem[K] = A */ 320 PPC_MR(r_M + (K & 0xf), r_A); 321 ctx->seen |= SEEN_MEM | (1<<(K & 0xf)); 322 break; 323 case BPF_STX: /* mem[K] = X */ 324 PPC_MR(r_M + (K & 0xf), r_X); 325 ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf)); 326 break; 327 case BPF_LD | BPF_W | BPF_LEN: /* A = skb->len; */ 328 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4); 329 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len)); 330 break; 331 case BPF_LDX | BPF_W | BPF_ABS: /* A = *((u32 *)(seccomp_data + K)); */ 332 PPC_LWZ_OFFS(r_A, r_skb, K); 333 break; 334 case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */ 335 PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len)); 336 break; 337 338 /*** Ancillary info loads ***/ 339 case BPF_ANC | SKF_AD_PROTOCOL: /* A = ntohs(skb->protocol); */ 340 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, 341 protocol) != 2); 342 PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff, 343 protocol)); 344 break; 345 case BPF_ANC | SKF_AD_IFINDEX: 346 case BPF_ANC | SKF_AD_HATYPE: 347 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 348 ifindex) != 4); 349 BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, 350 type) != 2); 351 PPC_LL_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff, 352 dev)); 353 PPC_CMPDI(r_scratch1, 0); 354 if (ctx->pc_ret0 != -1) { 355 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]); 356 } else { 357 /* Exit, returning 0; first pass hits here. */ 358 PPC_BCC_SHORT(COND_NE, ctx->idx * 4 + 12); 359 PPC_LI(r_ret, 0); 360 PPC_JMP(exit_addr); 361 } 362 if (code == (BPF_ANC | SKF_AD_IFINDEX)) { 363 PPC_LWZ_OFFS(r_A, r_scratch1, 364 offsetof(struct net_device, ifindex)); 365 } else { 366 PPC_LHZ_OFFS(r_A, r_scratch1, 367 offsetof(struct net_device, type)); 368 } 369 370 break; 371 case BPF_ANC | SKF_AD_MARK: 372 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4); 373 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 374 mark)); 375 break; 376 case BPF_ANC | SKF_AD_RXHASH: 377 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4); 378 PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 379 hash)); 380 break; 381 case BPF_ANC | SKF_AD_VLAN_TAG: 382 BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2); 383 384 PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, 385 vlan_tci)); 386 break; 387 case BPF_ANC | SKF_AD_VLAN_TAG_PRESENT: 388 PPC_LBZ_OFFS(r_A, r_skb, PKT_VLAN_PRESENT_OFFSET()); 389 if (PKT_VLAN_PRESENT_BIT) 390 PPC_SRWI(r_A, r_A, PKT_VLAN_PRESENT_BIT); 391 if (PKT_VLAN_PRESENT_BIT < 7) 392 PPC_ANDI(r_A, r_A, 1); 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