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 "bpf_jit.h"
  17
  18 #ifndef __BIG_ENDIAN
  19 /* There are endianness assumptions herein. */
  20 #error "Little-endian PPC not supported in BPF compiler"
  21 #endif
  22
  23 int bpf_jit_enable __read_mostly;
  24
  25
  26 static inline void bpf_flush_icache(void *start, void *end)
  27 {
  28         smp_wmb();
  29         flush_icache_range((unsigned long)start, (unsigned long)end);
  30 }
  31
  32 static void bpf_jit_build_prologue(struct sk_filter *fp, u32 *image,
  33                                    struct codegen_context *ctx)
  34 {
  35         int i;
  36         const struct sock_filter *filter = fp->insns;
  37
  38         if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
  39                 /* Make stackframe */
  40                 if (ctx->seen & SEEN_DATAREF) {
  41                         /* If we call any helpers (for loads), save LR */
  42                         EMIT(PPC_INST_MFLR | __PPC_RT(0));
  43                         PPC_STD(0, 1, 16);
  44
  45                         /* Back up non-volatile regs. */
  46                         PPC_STD(r_D, 1, -(8*(32-r_D)));
  47                         PPC_STD(r_HL, 1, -(8*(32-r_HL)));
  48                 }
  49                 if (ctx->seen & SEEN_MEM) {
  50                         /*
  51                          * Conditionally save regs r15-r31 as some will be used
  52                          * for M[] data.
  53                          */
  54                         for (i = r_M; i < (r_M+16); i++) {
  55                                 if (ctx->seen & (1 << (i-r_M)))
  56                                         PPC_STD(i, 1, -(8*(32-i)));
  57                         }
  58                 }
  59                 EMIT(PPC_INST_STDU | __PPC_RS(1) | __PPC_RA(1) |
  60                      (-BPF_PPC_STACKFRAME & 0xfffc));
  61         }
  62
  63         if (ctx->seen & SEEN_DATAREF) {
  64                 /*
  65                  * If this filter needs to access skb data,
  66                  * prepare r_D and r_HL:
  67                  *  r_HL = skb->len - skb->data_len
  68                  *  r_D  = skb->data
  69                  */
  70                 PPC_LWZ_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
  71                                                          data_len));
  72                 PPC_LWZ_OFFS(r_HL, r_skb, offsetof(struct sk_buff, len));
  73                 PPC_SUB(r_HL, r_HL, r_scratch1);
  74                 PPC_LD_OFFS(r_D, r_skb, offsetof(struct sk_buff, data));
  75         }
  76
  77         if (ctx->seen & SEEN_XREG) {
  78                 /*
  79                  * TODO: Could also detect whether first instr. sets X and
  80                  * avoid this (as below, with A).
  81                  */
  82                 PPC_LI(r_X, 0);
  83         }
  84
  85         switch (filter[0].code) {
  86         case BPF_S_RET_K:
  87         case BPF_S_LD_W_LEN:
  88         case BPF_S_ANC_PROTOCOL:
  89         case BPF_S_ANC_IFINDEX:
  90         case BPF_S_ANC_MARK:
  91         case BPF_S_ANC_RXHASH:
  92         case BPF_S_ANC_CPU:
  93         case BPF_S_ANC_QUEUE:
  94         case BPF_S_LD_W_ABS:
  95         case BPF_S_LD_H_ABS:
  96         case BPF_S_LD_B_ABS:
  97                 /* first instruction sets A register (or is RET 'constant') */
  98                 break;
  99         default:
 100                 /* make sure we dont leak kernel information to user */
 101                 PPC_LI(r_A, 0);
 102         }
 103 }
 104
 105 static void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
 106 {
 107         int i;
 108
 109         if (ctx->seen & (SEEN_MEM | SEEN_DATAREF)) {
 110                 PPC_ADDI(1, 1, BPF_PPC_STACKFRAME);
 111                 if (ctx->seen & SEEN_DATAREF) {
 112                         PPC_LD(0, 1, 16);
 113                         PPC_MTLR(0);
 114                         PPC_LD(r_D, 1, -(8*(32-r_D)));
 115                         PPC_LD(r_HL, 1, -(8*(32-r_HL)));
 116                 }
 117                 if (ctx->seen & SEEN_MEM) {
 118                         /* Restore any saved non-vol registers */
 119                         for (i = r_M; i < (r_M+16); i++) {
 120                                 if (ctx->seen & (1 << (i-r_M)))
 121                                         PPC_LD(i, 1, -(8*(32-i)));
 122                         }
 123                 }
 124         }
 125         /* The RETs have left a return value in R3. */
 126
 127         PPC_BLR();
 128 }
 129
 130 /* Assemble the body code between the prologue & epilogue. */
 131 static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
 132                               struct codegen_context *ctx,
 133                               unsigned int *addrs)
 134 {
 135         const struct sock_filter *filter = fp->insns;
 136         int flen = fp->len;
 137         u8 *func;
 138         unsigned int true_cond;
 139         int i;
 140
 141         /* Start of epilogue code */
 142         unsigned int exit_addr = addrs[flen];
 143
 144         for (i = 0; i < flen; i++) {
 145                 unsigned int K = filter[i].k;
 146
 147                 /*
 148                  * addrs[] maps a BPF bytecode address into a real offset from
 149                  * the start of the body code.
 150                  */
 151                 addrs[i] = ctx->idx * 4;
 152
 153                 switch (filter[i].code) {
 154                         /*** ALU ops ***/
 155                 case BPF_S_ALU_ADD_X: /* A += X; */
 156                         ctx->seen |= SEEN_XREG;
 157                         PPC_ADD(r_A, r_A, r_X);
 158                         break;
 159                 case BPF_S_ALU_ADD_K: /* A += K; */
 160                         if (!K)
 161                                 break;
 162                         PPC_ADDI(r_A, r_A, IMM_L(K));
 163                         if (K >= 32768)
 164                                 PPC_ADDIS(r_A, r_A, IMM_HA(K));
 165                         break;
 166                 case BPF_S_ALU_SUB_X: /* A -= X; */
 167                         ctx->seen |= SEEN_XREG;
 168                         PPC_SUB(r_A, r_A, r_X);
 169                         break;
 170                 case BPF_S_ALU_SUB_K: /* A -= K */
 171                         if (!K)
 172                                 break;
 173                         PPC_ADDI(r_A, r_A, IMM_L(-K));
 174                         if (K >= 32768)
 175                                 PPC_ADDIS(r_A, r_A, IMM_HA(-K));
 176                         break;
 177                 case BPF_S_ALU_MUL_X: /* A *= X; */
 178                         ctx->seen |= SEEN_XREG;
 179                         PPC_MUL(r_A, r_A, r_X);
 180                         break;
 181                 case BPF_S_ALU_MUL_K: /* A *= K */
 182                         if (K < 32768)
 183                                 PPC_MULI(r_A, r_A, K);
 184                         else {
 185                                 PPC_LI32(r_scratch1, K);
 186                                 PPC_MUL(r_A, r_A, r_scratch1);
 187                         }
 188                         break;
 189                 case BPF_S_ALU_DIV_X: /* A /= X; */
 190                         ctx->seen |= SEEN_XREG;
 191                         PPC_CMPWI(r_X, 0);
 192                         if (ctx->pc_ret0 != -1) {
 193                                 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
 194                         } else {
 195                                 /*
 196                                  * Exit, returning 0; first pass hits here
 197                                  * (longer worst-case code size).
 198                                  */
 199                                 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
 200                                 PPC_LI(r_ret, 0);
 201                                 PPC_JMP(exit_addr);
 202                         }
 203                         PPC_DIVWU(r_A, r_A, r_X);
 204                         break;
 205                 case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
 206                         PPC_LI32(r_scratch1, K);
 207                         /* Top 32 bits of 64bit result -> A */
 208                         PPC_MULHWU(r_A, r_A, r_scratch1);
 209                         break;
 210                 case BPF_S_ALU_AND_X:
 211                         ctx->seen |= SEEN_XREG;
 212                         PPC_AND(r_A, r_A, r_X);
 213                         break;
 214                 case BPF_S_ALU_AND_K:
 215                         if (!IMM_H(K))
 216                                 PPC_ANDI(r_A, r_A, K);
 217                         else {
 218                                 PPC_LI32(r_scratch1, K);
 219                                 PPC_AND(r_A, r_A, r_scratch1);
 220                         }
 221                         break;
 222                 case BPF_S_ALU_OR_X:
 223                         ctx->seen |= SEEN_XREG;
 224                         PPC_OR(r_A, r_A, r_X);
 225                         break;
 226                 case BPF_S_ALU_OR_K:
 227                         if (IMM_L(K))
 228                                 PPC_ORI(r_A, r_A, IMM_L(K));
 229                         if (K >= 65536)
 230                                 PPC_ORIS(r_A, r_A, IMM_H(K));
 231                         break;
 232                 case BPF_S_ALU_LSH_X: /* A <<= X; */
 233                         ctx->seen |= SEEN_XREG;
 234                         PPC_SLW(r_A, r_A, r_X);
 235                         break;
 236                 case BPF_S_ALU_LSH_K:
 237                         if (K == 0)
 238                                 break;
 239                         else
 240                                 PPC_SLWI(r_A, r_A, K);
 241                         break;
 242                 case BPF_S_ALU_RSH_X: /* A >>= X; */
 243                         ctx->seen |= SEEN_XREG;
 244                         PPC_SRW(r_A, r_A, r_X);
 245                         break;
 246                 case BPF_S_ALU_RSH_K: /* A >>= K; */
 247                         if (K == 0)
 248                                 break;
 249                         else
 250                                 PPC_SRWI(r_A, r_A, K);
 251                         break;
 252                 case BPF_S_ALU_NEG:
 253                         PPC_NEG(r_A, r_A);
 254                         break;
 255                 case BPF_S_RET_K:
 256                         PPC_LI32(r_ret, K);
 257                         if (!K) {
 258                                 if (ctx->pc_ret0 == -1)
 259                                         ctx->pc_ret0 = i;
 260                         }
 261                         /*
 262                          * If this isn't the very last instruction, branch to
 263                          * the epilogue if we've stuff to clean up.  Otherwise,
 264                          * if there's nothing to tidy, just return.  If we /are/
 265                          * the last instruction, we're about to fall through to
 266                          * the epilogue to return.
 267                          */
 268                         if (i != flen - 1) {
 269                                 /*
 270                                  * Note: 'seen' is properly valid only on pass
 271                                  * #2.  Both parts of this conditional are the
 272                                  * same instruction size though, meaning the
 273                                  * first pass will still correctly determine the
 274                                  * code size/addresses.
 275                                  */
 276                                 if (ctx->seen)
 277                                         PPC_JMP(exit_addr);
 278                                 else
 279                                         PPC_BLR();
 280                         }
 281                         break;
 282                 case BPF_S_RET_A:
 283                         PPC_MR(r_ret, r_A);
 284                         if (i != flen - 1) {
 285                                 if (ctx->seen)
 286                                         PPC_JMP(exit_addr);
 287                                 else
 288                                         PPC_BLR();
 289                         }
 290                         break;
 291                 case BPF_S_MISC_TAX: /* X = A */
 292                         PPC_MR(r_X, r_A);
 293                         break;
 294                 case BPF_S_MISC_TXA: /* A = X */
 295                         ctx->seen |= SEEN_XREG;
 296                         PPC_MR(r_A, r_X);
 297                         break;
 298
 299                         /*** Constant loads/M[] access ***/
 300                 case BPF_S_LD_IMM: /* A = K */
 301                         PPC_LI32(r_A, K);
 302                         break;
 303                 case BPF_S_LDX_IMM: /* X = K */
 304                         PPC_LI32(r_X, K);
 305                         break;
 306                 case BPF_S_LD_MEM: /* A = mem[K] */
 307                         PPC_MR(r_A, r_M + (K & 0xf));
 308                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 309                         break;
 310                 case BPF_S_LDX_MEM: /* X = mem[K] */
 311                         PPC_MR(r_X, r_M + (K & 0xf));
 312                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 313                         break;
 314                 case BPF_S_ST: /* mem[K] = A */
 315                         PPC_MR(r_M + (K & 0xf), r_A);
 316                         ctx->seen |= SEEN_MEM | (1<<(K & 0xf));
 317                         break;
 318                 case BPF_S_STX: /* mem[K] = X */
 319                         PPC_MR(r_M + (K & 0xf), r_X);
 320                         ctx->seen |= SEEN_XREG | SEEN_MEM | (1<<(K & 0xf));
 321                         break;
 322                 case BPF_S_LD_W_LEN: /* A = skb->len; */
 323                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
 324                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
 325                         break;
 326                 case BPF_S_LDX_W_LEN: /* X = skb->len; */
 327                         PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
 328                         break;
 329
 330                         /*** Ancillary info loads ***/
 331
 332                         /* None of the BPF_S_ANC* codes appear to be passed by
 333                          * sk_chk_filter().  The interpreter and the x86 BPF
 334                          * compiler implement them so we do too -- they may be
 335                          * planted in future.
 336                          */
 337                 case BPF_S_ANC_PROTOCOL: /* A = ntohs(skb->protocol); */
 338                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
 339                                                   protocol) != 2);
 340                         PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 341                                                           protocol));
 342                         /* ntohs is a NOP with BE loads. */
 343                         break;
 344                 case BPF_S_ANC_IFINDEX:
 345                         PPC_LD_OFFS(r_scratch1, r_skb, offsetof(struct sk_buff,
 346                                                                 dev));
 347                         PPC_CMPDI(r_scratch1, 0);
 348                         if (ctx->pc_ret0 != -1) {
 349                                 PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
 350                         } else {
 351                                 /* Exit, returning 0; first pass hits here. */
 352                                 PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
 353                                 PPC_LI(r_ret, 0);
 354                                 PPC_JMP(exit_addr);
 355                         }
 356                         BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
 357                                                   ifindex) != 4);
 358                         PPC_LWZ_OFFS(r_A, r_scratch1,
 359                                      offsetof(struct net_device, ifindex));
 360                         break;
 361                 case BPF_S_ANC_MARK:
 362                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
 363                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 364                                                           mark));
 365                         break;
 366                 case BPF_S_ANC_RXHASH:
 367                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
 368                         PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 369                                                           rxhash));
 370                         break;
 371                 case BPF_S_ANC_QUEUE:
 372                         BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
 373                                                   queue_mapping) != 2);
 374                         PPC_LHZ_OFFS(r_A, r_skb, offsetof(struct sk_buff,
 375                                                           queue_mapping));
 376                         break;
 377                 case BPF_S_ANC_CPU:
 378 #ifdef CONFIG_SMP
 379                         /*
 380                          * PACA ptr is r13:
 381                          * raw_smp_processor_id() = local_paca->paca_index
 382                          */
 383                         BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct,
 384                                                   paca_index) != 2);
 385                         PPC_LHZ_OFFS(r_A, 13,
 386                                      offsetof(struct paca_struct, paca_index));
 387 #else
 388                         PPC_LI(r_A, 0);
 389 #endif
 390                         break;
 391
 392                         /*** Absolute loads from packet header/data ***/
 393                 case BPF_S_LD_W_ABS:
 394                         func = sk_load_word;
 395                         goto common_load;
 396                 case BPF_S_LD_H_ABS:
 397                         func = sk_load_half;
 398                         goto common_load;
 399                 case BPF_S_LD_B_ABS:
 400                         func = sk_load_byte;
 401                 common_load:
 402                         /*
 403                          * Load from [K].  Reference with the (negative)
 404                          * SKF_NET_OFF/SKF_LL_OFF offsets is unsupported.
 405                          */
 406                         ctx->seen |= SEEN_DATAREF;
 407                         if ((int)K < 0)
 408                                 return -ENOTSUPP;
 409                         PPC_LI64(r_scratch1, func);
 410                         PPC_MTLR(r_scratch1);
 411                         PPC_LI32(r_addr, K);
 412                         PPC_BLRL();
 413                         /*
 414                          * Helper returns 'lt' condition on error, and an
 415                          * appropriate return value in r3
 416                          */
 417                         PPC_BCC(COND_LT, exit_addr);
 418                         break;
 419
 420                         /*** Indirect loads from packet header/data ***/
 421                 case BPF_S_LD_W_IND:
 422                         func = sk_load_word;
 423                         goto common_load_ind;
 424                 case BPF_S_LD_H_IND:
 425                         func = sk_load_half;
 426                         goto common_load_ind;
 427                 case BPF_S_LD_B_IND:
 428                         func = sk_load_byte;
 429                 common_load_ind:
 430                         /*
 431                          * Load from [X + K].  Negative offsets are tested for
 432                          * in the helper functions, and result in a 'ret 0'.
 433                          */
 434                         ctx->seen |= SEEN_DATAREF | SEEN_XREG;
 435                         PPC_LI64(r_scratch1, func);
 436                         PPC_MTLR(r_scratch1);
 437                         PPC_ADDI(r_addr, r_X, IMM_L(K));
 438                         if (K >= 32768)
 439                                 PPC_ADDIS(r_addr, r_addr, IMM_HA(K));
 440                         PPC_BLRL();
 441                         /* If error, cr0.LT set */
 442                         PPC_BCC(COND_LT, exit_addr);
 443                         break;
 444
 445                 case BPF_S_LDX_B_MSH:
 446                         /*
 447                          * x86 version drops packet (RET 0) when K<0, whereas
 448                          * interpreter does allow K<0 (__load_pointer, special
 449                          * ancillary data).  common_load returns ENOTSUPP if K<0,
 450                          * so we fall back to interpreter & filter works.
 451                          */
 452                         func = sk_load_byte_msh;
 453                         goto common_load;
 454                         break;
 455
 456                         /*** Jump and branches ***/
 457                 case BPF_S_JMP_JA:
 458                         if (K != 0)
 459                                 PPC_JMP(addrs[i + 1 + K]);
 460                         break;
 461
 462                 case BPF_S_JMP_JGT_K:
 463                 case BPF_S_JMP_JGT_X:
 464                         true_cond = COND_GT;
 465                         goto cond_branch;
 466                 case BPF_S_JMP_JGE_K:
 467                 case BPF_S_JMP_JGE_X:
 468                         true_cond = COND_GE;
 469                         goto cond_branch;
 470                 case BPF_S_JMP_JEQ_K:
 471                 case BPF_S_JMP_JEQ_X:
 472                         true_cond = COND_EQ;
 473                         goto cond_branch;
 474                 case BPF_S_JMP_JSET_K:
 475                 case BPF_S_JMP_JSET_X:
 476                         true_cond = COND_NE;
 477                         /* Fall through */
 478                 cond_branch:
 479                         /* same targets, can avoid doing the test :) */
 480                         if (filter[i].jt == filter[i].jf) {
 481                                 if (filter[i].jt > 0)
 482                                         PPC_JMP(addrs[i + 1 + filter[i].jt]);
 483                                 break;
 484                         }
 485
 486                         switch (filter[i].code) {
 487                         case BPF_S_JMP_JGT_X:
 488                         case BPF_S_JMP_JGE_X:
 489                         case BPF_S_JMP_JEQ_X:
 490                                 ctx->seen |= SEEN_XREG;
 491                                 PPC_CMPLW(r_A, r_X);
 492                                 break;
 493                         case BPF_S_JMP_JSET_X:
 494                                 ctx->seen |= SEEN_XREG;
 495                                 PPC_AND_DOT(r_scratch1, r_A, r_X);
 496                                 break;
 497                         case BPF_S_JMP_JEQ_K:
 498                         case BPF_S_JMP_JGT_K:
 499                         case BPF_S_JMP_JGE_K:
 500                                 if (K < 32768)
 501                                         PPC_CMPLWI(r_A, K);
 502                                 else {
 503                                         PPC_LI32(r_scratch1, K);
 504                                         PPC_CMPLW(r_A, r_scratch1);
 505                                 }
 506                                 break;
 507                         case BPF_S_JMP_JSET_K:
 508                                 if (K < 32768)
 509                                         /* PPC_ANDI is /only/ dot-form */
 510                                         PPC_ANDI(r_scratch1, r_A, K);
 511                                 else {
 512                                         PPC_LI32(r_scratch1, K);
 513                                         PPC_AND_DOT(r_scratch1, r_A,
 514                                                     r_scratch1);
 515                                 }
 516                                 break;
 517                         }
 518                         /* Sometimes branches are constructed "backward", with
 519                          * the false path being the branch and true path being
 520                          * a fallthrough to the next instruction.
 521                          */
 522                         if (filter[i].jt == 0)
 523                                 /* Swap the sense of the branch */
 524                                 PPC_BCC(true_cond ^ COND_CMP_TRUE,
 525                                         addrs[i + 1 + filter[i].jf]);
 526                         else {
 527                                 PPC_BCC(true_cond, addrs[i + 1 + filter[i].jt]);
 528                                 if (filter[i].jf != 0)
 529                                         PPC_JMP(addrs[i + 1 + filter[i].jf]);
 530                         }
 531                         break;
 532                 default:
 533                         /* The filter contains something cruel & unusual.
 534                          * We don't handle it, but also there shouldn't be
 535                          * anything missing from our list.
 536                          */
 537                         if (printk_ratelimit())
 538                                 pr_err("BPF filter opcode %04x (@%d) unsupported\n",
 539                                        filter[i].code, i);
 540                         return -ENOTSUPP;
 541                 }
 542
 543         }
 544         /* Set end-of-body-code address for exit. */
 545         addrs[i] = ctx->idx * 4;
 546
 547         return 0;
 548 }
 549
 550 void bpf_jit_compile(struct sk_filter *fp)
 551 {
 552         unsigned int proglen;
 553         unsigned int alloclen;
 554         u32 *image = NULL;
 555         u32 *code_base;
 556         unsigned int *addrs;
 557         struct codegen_context cgctx;
 558         int pass;
 559         int flen = fp->len;
 560
 561         if (!bpf_jit_enable)
 562                 return;
 563
 564         addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
 565         if (addrs == NULL)
 566                 return;
 567
 568         /*
 569          * There are multiple assembly passes as the generated code will change
 570          * size as it settles down, figuring out the max branch offsets/exit
 571          * paths required.
 572          *
 573          * The range of standard conditional branches is +/- 32Kbytes.  Since
 574          * BPF_MAXINSNS = 4096, we can only jump from (worst case) start to
 575          * finish with 8 bytes/instruction.  Not feasible, so long jumps are
 576          * used, distinct from short branches.
 577          *
 578          * Current:
 579          *
 580          * For now, both branch types assemble to 2 words (short branches padded
 581          * with a NOP); this is less efficient, but assembly will always complete
 582          * after exactly 3 passes:
 583          *
 584          * First pass: No code buffer; Program is "faux-generated" -- no code
 585          * emitted but maximum size of output determined (and addrs[] filled
 586          * in).  Also, we note whether we use M[], whether we use skb data, etc.
 587          * All generation choices assumed to be 'worst-case', e.g. branches all
 588          * far (2 instructions), return path code reduction not available, etc.
 589          *
 590          * Second pass: Code buffer allocated with size determined previously.
 591          * Prologue generated to support features we have seen used.  Exit paths
 592          * determined and addrs[] is filled in again, as code may be slightly
 593          * smaller as a result.
 594          *
 595          * Third pass: Code generated 'for real', and branch destinations
 596          * determined from now-accurate addrs[] map.
 597          *
 598          * Ideal:
 599          *
 600          * If we optimise this, near branches will be shorter.  On the
 601          * first assembly pass, we should err on the side of caution and
 602          * generate the biggest code.  On subsequent passes, branches will be
 603          * generated short or long and code size will reduce.  With smaller
 604          * code, more branches may fall into the short category, and code will
 605          * reduce more.
 606          *
 607          * Finally, if we see one pass generate code the same size as the
 608          * previous pass we have converged and should now generate code for
 609          * real.  Allocating at the end will also save the memory that would
 610          * otherwise be wasted by the (small) current code shrinkage.
 611          * Preferably, we should do a small number of passes (e.g. 5) and if we
 612          * haven't converged by then, get impatient and force code to generate
 613          * as-is, even if the odd branch would be left long.  The chances of a
 614          * long jump are tiny with all but the most enormous of BPF filter
 615          * inputs, so we should usually converge on the third pass.
 616          */
 617
 618         cgctx.idx = 0;
 619         cgctx.seen = 0;
 620         cgctx.pc_ret0 = -1;
 621         /* Scouting faux-generate pass 0 */
 622         if (bpf_jit_build_body(fp, 0, &cgctx, addrs))
 623                 /* We hit something illegal or unsupported. */
 624                 goto out;
 625
 626         /*
 627          * Pretend to build prologue, given the features we've seen.  This will
 628          * update ctgtx.idx as it pretends to output instructions, then we can
 629          * calculate total size from idx.
 630          */
 631         bpf_jit_build_prologue(fp, 0, &cgctx);
 632         bpf_jit_build_epilogue(0, &cgctx);
 633
 634         proglen = cgctx.idx * 4;
 635         alloclen = proglen + FUNCTION_DESCR_SIZE;
 636         image = module_alloc(max_t(unsigned int, alloclen,
 637                                    sizeof(struct work_struct)));
 638         if (!image)
 639                 goto out;
 640
 641         code_base = image + (FUNCTION_DESCR_SIZE/4);
 642
 643         /* Code generation passes 1-2 */
 644         for (pass = 1; pass < 3; pass++) {
 645                 /* Now build the prologue, body code & epilogue for real. */
 646                 cgctx.idx = 0;
 647                 bpf_jit_build_prologue(fp, code_base, &cgctx);
 648                 bpf_jit_build_body(fp, code_base, &cgctx, addrs);
 649                 bpf_jit_build_epilogue(code_base, &cgctx);
 650
 651                 if (bpf_jit_enable > 1)
 652                         pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
 653                                 proglen - (cgctx.idx * 4), cgctx.seen);
 654         }
 655
 656         if (bpf_jit_enable > 1)
 657                 pr_info("flen=%d proglen=%u pass=%d image=%p\n",
 658                        flen, proglen, pass, image);
 659
 660         if (image) {
 661                 if (bpf_jit_enable > 1)
 662                         print_hex_dump(KERN_ERR, "JIT code: ",
 663                                        DUMP_PREFIX_ADDRESS,
 664                                        16, 1, code_base,
 665                                        proglen, false);
 666
 667                 bpf_flush_icache(code_base, code_base + (proglen/4));
 668                 /* Function descriptor nastiness: Address + TOC */
 669                 ((u64 *)image)[0] = (u64)code_base;
 670                 ((u64 *)image)[1] = local_paca->kernel_toc;
 671                 fp->bpf_func = (void *)image;
 672         }
 673 out:
 674         kfree(addrs);
 675         return;
 676 }
 677
 678 static void jit_free_defer(struct work_struct *arg)
 679 {
 680         module_free(NULL, arg);
 681 }
 682
 683 /* run from softirq, we must use a work_struct to call
 684  * module_free() from process context
 685  */
 686 void bpf_jit_free(struct sk_filter *fp)
 687 {
 688         if (fp->bpf_func != sk_run_filter) {
 689                 struct work_struct *work = (struct work_struct *)fp->bpf_func;
 690
 691                 INIT_WORK(work, jit_free_defer);
 692                 schedule_work(work);
 693         }
 694 }