arch/powerpc/net/bpf_jit_comp.c

   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_DIV_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                                 /*
 197                                  * Exit, returning 0; first pass hits here
 198                                  * (longer worst-case code size).
 199                                  */
 200                                 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
 201                                 PPC_LI(r_ret, 0);
 202                                 PPC_JMP(exit_addr);
 203                         }
 204                         PPC_DIVWU(r_A, r_A, r_X);
 205                         break;
 206                 case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
 207                         PPC_LI32(r_scratch1, K);
 208                         /* Top 32 bits of 64bit result -> A */
 209                         PPC_MULHWU(r_A, r_A, r_scratch1);
 210                         break;
 211                 case BPF_S_ALU_AND_X:
 212                         ctx->seen |= SEEN_XREG;
 213                         PPC_AND(r_A, r_A, r_X);
 214                         break;
 215                 case BPF_S_ALU_AND_K:
 216                         if (!IMM_H(K))
 217                                 PPC_ANDI(r_A, r_A, K);
 218                         else {
 219                                 PPC_LI32(r_scratch1, K);
 220                                 PPC_AND(r_A, r_A, r_scratch1);
 221                         }
 222                         break;
 223                 case BPF_S_ALU_OR_X:
 224                         ctx->seen |= SEEN_XREG;
 225                         PPC_OR(r_A, r_A, r_X);
 226                         break;
 227                 case BPF_S_ALU_OR_K:
 228                         if (IMM_L(K))
 229                                 PPC_ORI(r_A, r_A, IMM_L(K));
 230                         if (K >= 65536)
 231                                 PPC_ORIS(r_A, r_A, IMM_H(K));
 232                         break;
 233                 case BPF_S_ANC_ALU_XOR_X:
 234                 case BPF_S_ALU_XOR_X: /* A ^= X */
 235                         ctx->seen |= SEEN_XREG;
 236                         PPC_XOR(r_A, r_A, r_X);
 237                         break;
 238                 case BPF_S_ALU_XOR_K: /* A ^= K */
 239                         if (IMM_L(K))
 240                                 PPC_XORI(r_A, r_A, IMM_L(K));
 241                         if (K >= 65536)
 242                                 PPC_XORIS(r_A, r_A, IMM_H(K));
 243                         break;
 244                 case BPF_S_ALU_LSH_X: /* A <<= X; */
 245                         ctx->seen |= SEEN_XREG;
 246                         PPC_SLW(r_A, r_A, r_X);
 247                         break;
 248                 case BPF_S_ALU_LSH_K:
 249                         if (K == 0)
 250                                 break;
 251                         else
 252                                 PPC_SLWI(r_A, r_A, K);
 253                         break;
 254                 case BPF_S_ALU_RSH_X: /* A >>= X; */
 255                         ctx->seen |= SEEN_XREG;
 256                         PPC_SRW(r_A, r_A, r_X);
 257                         break;
 258                 case BPF_S_ALU_RSH_K: /* A >>= K; */
 259                         if (K == 0)
 260                                 break;
 261                         else
 262                                 PPC_SRWI(r_A, r_A, K);
 263                         break;
 264                 case BPF_S_ALU_NEG:
 265                         PPC_NEG(r_A, r_A);
 266                         break;
 267                 case BPF_S_RET_K:
 268                         PPC_LI32(r_ret, K);
 269                         if (!K) {
 270                                 if (ctx->pc_ret0 == -1)
 271                                         ctx->pc_ret0 = i;
 272                         }
 273                         /*
 274                          * If this isn't the very last instruction, branch to
 275                          * the epilogue if we've stuff to clean up.  Otherwise,
 276                          * if there's nothing to tidy, just return.  If we /are/
 277                          * the last instruction, we're about to fall through to
 278                          * the epilogue to return.
 279                          */
 280                         if (i != flen - 1) {
 281                                 /*
 282                                  * Note: 'seen' is properly valid only on pass
 283                                  * #2.  Both parts of this conditional are the
 284                                  * same instruction size though, meaning the
 285                                  * first pass will still correctly determine the
 286                                  * code size/addresses.
 287                                  */
 288                                 if (ctx->seen)
 289                                         PPC_JMP(exit_addr);
 290                                 else
 291                                         PPC_BLR();
 292                         }
 293                         break;
 294                 case BPF_S_RET_A:
 295                         PPC_MR(r_ret, r_A);
 296                         if (i != flen - 1) {
 297                                 if (ctx->seen)
 298                                         PPC_JMP(exit_addr);
 299                                 else
 300                                         PPC_BLR();
 301                         }
 302                         break;
 303                 case BPF_S_MISC_TAX: /* X = A */
 304                         PPC_MR(r_X, r_A);
 305                         break;
 306                 case BPF_S_MISC_TXA: /* A = X */
 307                         ctx->seen |= SEEN_XREG;
 308                         PPC_MR(r_A, r_X);
 309                         break;
 310
 311                         /*** Constant loads/M[] access ***/
 312                 case BPF_S_LD_IMM: /* A = K */
 313                         PPC_LI32(r_A, K);
 314                         break;
 315                 case BPF_S_LDX_IMM: /* X = K */
 316                         PPC_LI32(r_X, K);
 317                         break;
 318                 case BPF_S_LD_MEM: /* A = mem[K] */
 319                         PPC_MR(r_A, r_M + (K & 0xf));
 320                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 321                         break;
 322                 case BPF_S_LDX_MEM: /* X = mem[K] */
 323                         PPC_MR(r_X, r_M + (K & 0xf));
 324                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 325                         break;
 326                 case BPF_S_ST: /* mem[K] = A */
 327                         PPC_MR(r_M + (K & 0xf), r_A);
 328                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 329                         break;
 330                 case BPF_S_STX: /* mem[K] = X */
 331                         PPC_MR(r_M + (K & 0xf), r_X);
 332                         ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
 333                         break;
 334                 case BPF_S_LD_W_LEN: /* A = skb->len; */
 335                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
 336                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
 337                         break;
 338                 case BPF_S_LDX_W_LEN: /* X = skb->len; */
 339                         PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
 340                         break;
 341
 342                         /*** Ancillary info loads ***/
 343                 case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */
 344                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
 345                                                   protocol) != 2);
 346                         PPC_NTOHS_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 347                                                             protocol));
 348                         break;
 349                 case BPF_S_ANC_IFINDEX:
 350                         PPC_LD_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                         BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
 362                                                   ifindex) != 4);
 363                         PPC_LWZ_OFFS(r_A, r_scratch1,
 364                                      offsetof(struct net_device, ifindex));
 365                         break;
 366                 case BPF_S_ANC_MARK:
 367                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
 368                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 369                                                           mark));
 370                         break;
 371                 case BPF_S_ANC_RXHASH:
 372                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
 373                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 374                                                           rxhash));
 375                         break;
 376                 case BPF_S_ANC_VLAN_TAG:
 377                 case BPF_S_ANC_VLAN_TAG_PRESENT:
 378                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
 379                         PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 380                                                           vlan_tci));
 381                         if (filter[i].code == BPF_S_ANC_VLAN_TAG)
 382                                 PPC_ANDI(r_A, r_A, VLAN_VID_MASK);
 383                         else
 384                                 PPC_ANDI(r_A, r_A, VLAN_TAG_PRESENT);
 385                         break;
 386                 case BPF_S_ANC_QUEUE:
 387                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
 388                                                   queue_mapping) != 2);
 389                         PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 390                                                           queue_mapping));
 391                         break;
 392                 case BPF_S_ANC_CPU:
 393 #ifdef CONFIG_SMP
 394                         /*
 395                          * PACA ptr is r13:
 396                          * raw_smp_processor_id() = local_paca->paca_index
 397                          */
 398                         BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct,
 399                                                   paca_index) != 2);
 400                         PPC_LHZ_OFFS(r_A, 13,
 401                                      offsetof(struct paca_struct, paca_index));
 402 #else
 403                         PPC_LI(r_A, 0);
 404 #endif
 405                         break;
 406
 407                         /*** Absolute loads from packet header/data ***/
 408                 case BPF_S_LD_W_ABS:
 409                         func = CHOOSE_LOAD_FUNC(K, sk_load_word);
 410                         goto common_load;
 411                 case BPF_S_LD_H_ABS:
 412                         func = CHOOSE_LOAD_FUNC(K, sk_load_half);
 413                         goto common_load;
 414                 case BPF_S_LD_B_ABS:
 415                         func = CHOOSE_LOAD_FUNC(K, sk_load_byte);
 416                 common_load:
 417                         /* Load from [K]. */
 418                         ctx->seen |= SEEN_DATAREF;
 419                         PPC_LI64(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_S_LD_W_IND:
 432                         func = sk_load_word;
 433                         goto common_load_ind;
 434                 case BPF_S_LD_H_IND:
 435                         func = sk_load_half;
 436                         goto common_load_ind;
 437                 case BPF_S_LD_B_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_LI64(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_S_LDX_B_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_S_JMP_JA:
 462                         if (K != 0)
 463                                 PPC_JMP(addrs[i + 1 + K]);
 464                         break;
 465
 466                 case BPF_S_JMP_JGT_K:
 467                 case BPF_S_JMP_JGT_X:
 468                         true_cond = COND_GT;
 469                         goto cond_branch;
 470                 case BPF_S_JMP_JGE_K:
 471                 case BPF_S_JMP_JGE_X:
 472                         true_cond = COND_GE;
 473                         goto cond_branch;
 474                 case BPF_S_JMP_JEQ_K:
 475                 case BPF_S_JMP_JEQ_X:
 476                         true_cond = COND_EQ;
 477                         goto cond_branch;
 478                 case BPF_S_JMP_JSET_K:
 479                 case BPF_S_JMP_JSET_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 (filter[i].code) {
 491                         case BPF_S_JMP_JGT_X:
 492                         case BPF_S_JMP_JGE_X:
 493                         case BPF_S_JMP_JEQ_X:
 494                                 ctx->seen |= SEEN_XREG;
 495                                 PPC_CMPLW(r_A, r_X);
 496                                 break;
 497                         case BPF_S_JMP_JSET_X:
 498                                 ctx->seen |= SEEN_XREG;
 499                                 PPC_AND_DOT(r_scratch1, r_A, r_X);
 500                                 break;
 501                         case BPF_S_JMP_JEQ_K:
 502                         case BPF_S_JMP_JGT_K:
 503                         case BPF_S_JMP_JGE_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_S_JMP_JSET_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 sk_filter *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                 /* Function descriptor nastiness: Address + TOC */
 668                 ((u64 *)image)[0] = (u64)code_base;
 669                 ((u64 *)image)[1] = local_paca->kernel_toc;
 670                 fp->bpf_func = (void *)image;
 671         }
 672 out:
 673         kfree(addrs);
 674         return;
 675 }
 676
 677 void bpf_jit_free(struct sk_filter *fp)
 678 {
 679         if (fp->bpf_func != sk_run_filter)
 680                 module_free(NULL, fp->bpf_func);
 681 }