linux/tools/net/bpf_jit_disasm.c
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   1/*
   2 * Minimal BPF JIT image disassembler
   3 *
   4 * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
   5 * debugging or verification purposes.
   6 *
   7 * To get the disassembly of the JIT code, do the following:
   8 *
   9 *  1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
  10 *  2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
  11 *  3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
  12 *
  13 * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
  14 * Licensed under the GNU General Public License, version 2.0 (GPLv2)
  15 */
  16
  17#include <stdint.h>
  18#include <stdio.h>
  19#include <stdlib.h>
  20#include <assert.h>
  21#include <unistd.h>
  22#include <string.h>
  23#include <bfd.h>
  24#include <dis-asm.h>
  25#include <sys/klog.h>
  26#include <sys/types.h>
  27#include <regex.h>
  28
  29static void get_exec_path(char *tpath, size_t size)
  30{
  31        char *path;
  32        ssize_t len;
  33
  34        snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
  35        tpath[size - 1] = 0;
  36
  37        path = strdup(tpath);
  38        assert(path);
  39
  40        len = readlink(path, tpath, size);
  41        tpath[len] = 0;
  42
  43        free(path);
  44}
  45
  46static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
  47                          int opcodes)
  48{
  49        int count, i, pc = 0;
  50        char tpath[256];
  51        struct disassemble_info info;
  52        disassembler_ftype disassemble;
  53        bfd *bfdf;
  54
  55        memset(tpath, 0, sizeof(tpath));
  56        get_exec_path(tpath, sizeof(tpath));
  57
  58        bfdf = bfd_openr(tpath, NULL);
  59        assert(bfdf);
  60        assert(bfd_check_format(bfdf, bfd_object));
  61
  62        init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
  63        info.arch = bfd_get_arch(bfdf);
  64        info.mach = bfd_get_mach(bfdf);
  65        info.buffer = image;
  66        info.buffer_length = len;
  67
  68        disassemble_init_for_target(&info);
  69
  70        disassemble = disassembler(bfdf);
  71        assert(disassemble);
  72
  73        do {
  74                printf("%4x:\t", pc);
  75
  76                count = disassemble(pc, &info);
  77
  78                if (opcodes) {
  79                        printf("\n\t");
  80                        for (i = 0; i < count; ++i)
  81                                printf("%02x ", (uint8_t) image[pc + i]);
  82                }
  83                printf("\n");
  84
  85                pc += count;
  86        } while(count > 0 && pc < len);
  87
  88        bfd_close(bfdf);
  89}
  90
  91static char *get_klog_buff(int *klen)
  92{
  93        int ret, len = klogctl(10, NULL, 0);
  94        char *buff = malloc(len);
  95
  96        assert(buff && klen);
  97        ret = klogctl(3, buff, len);
  98        assert(ret >= 0);
  99        *klen = ret;
 100
 101        return buff;
 102}
 103
 104static void put_klog_buff(char *buff)
 105{
 106        free(buff);
 107}
 108
 109static int get_last_jit_image(char *haystack, size_t hlen,
 110                              uint8_t *image, size_t ilen,
 111                              unsigned long *base)
 112{
 113        char *ptr, *pptr, *tmp;
 114        off_t off = 0;
 115        int ret, flen, proglen, pass, ulen = 0;
 116        regmatch_t pmatch[1];
 117        regex_t regex;
 118
 119        if (hlen == 0)
 120                return 0;
 121
 122        ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
 123                      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
 124        assert(ret == 0);
 125
 126        ptr = haystack;
 127        while (1) {
 128                ret = regexec(&regex, ptr, 1, pmatch, 0);
 129                if (ret == 0) {
 130                        ptr += pmatch[0].rm_eo;
 131                        off += pmatch[0].rm_eo;
 132                        assert(off < hlen);
 133                } else
 134                        break;
 135        }
 136
 137        ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
 138        ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
 139                     &flen, &proglen, &pass, base);
 140        if (ret != 4)
 141                return 0;
 142
 143        tmp = ptr = haystack + off;
 144        while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
 145                tmp = NULL;
 146                if (!strstr(ptr, "JIT code"))
 147                        continue;
 148                pptr = ptr;
 149                while ((ptr = strstr(pptr, ":")))
 150                        pptr = ptr + 1;
 151                ptr = pptr;
 152                do {
 153                        image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
 154                        if (ptr == pptr || ulen >= ilen) {
 155                                ulen--;
 156                                break;
 157                        }
 158                        ptr = pptr;
 159                } while (1);
 160        }
 161
 162        assert(ulen == proglen);
 163        printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
 164               proglen, pass, flen);
 165        printf("%lx + <x>:\n", *base);
 166
 167        regfree(&regex);
 168        return ulen;
 169}
 170
 171int main(int argc, char **argv)
 172{
 173        int len, klen, opcodes = 0;
 174        char *kbuff;
 175        unsigned long base;
 176        uint8_t image[4096];
 177
 178        if (argc > 1) {
 179                if (!strncmp("-o", argv[argc - 1], 2)) {
 180                        opcodes = 1;
 181                } else {
 182                        printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
 183                        exit(0);
 184                }
 185        }
 186
 187        bfd_init();
 188        memset(image, 0, sizeof(image));
 189
 190        kbuff = get_klog_buff(&klen);
 191
 192        len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
 193        if (len > 0 && base > 0)
 194                get_asm_insns(image, len, base, opcodes);
 195
 196        put_klog_buff(kbuff);
 197
 198        return 0;
 199}
 200
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