LXR linux/arch/powerpc/net/bpf_jit

   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
  23int bpf_jit_enable __read_mostly;
  24
  25
  26static 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
  32static 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
 105static 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. */
 131static 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
 550void 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        }
 673out:
 674        kfree(addrs);
 675        return;
 676}
 677
 678static 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 */
 686void 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}
 695