tools/net/bpf_jit_disasm.c

   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 <[email protected]>
  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
  29 static 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
  46 static 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
  91 static 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
 104 static void put_klog_buff(char *buff)
 105 {
 106         free(buff);
 107 }
 108
 109 static 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
 171 int 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 }