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 <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
  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, int opcodes)
  47 {
  48         int count, i, pc = 0;
  49         char tpath[256];
  50         struct disassemble_info info;
  51         disassembler_ftype disassemble;
  52         bfd *bfdf;
  53
  54         memset(tpath, 0, sizeof(tpath));
  55         get_exec_path(tpath, sizeof(tpath));
  56
  57         bfdf = bfd_openr(tpath, NULL);
  58         assert(bfdf);
  59         assert(bfd_check_format(bfdf, bfd_object));
  60
  61         init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
  62         info.arch = bfd_get_arch(bfdf);
  63         info.mach = bfd_get_mach(bfdf);
  64         info.buffer = image;
  65         info.buffer_length = len;
  66
  67         disassemble_init_for_target(&info);
  68
  69         disassemble = disassembler(bfdf);
  70         assert(disassemble);
  71
  72         do {
  73                 printf("%4x:\t", pc);
  74
  75                 count = disassemble(pc, &info);
  76
  77                 if (opcodes) {
  78                         printf("\n\t");
  79                         for (i = 0; i < count; ++i)
  80                                 printf("%02x ", (uint8_t) image[pc + i]);
  81                 }
  82                 printf("\n");
  83
  84                 pc += count;
  85         } while(count > 0 && pc < len);
  86
  87         bfd_close(bfdf);
  88 }
  89
  90 static char *get_klog_buff(int *klen)
  91 {
  92         int ret, len = klogctl(10, NULL, 0);
  93         char *buff = malloc(len);
  94
  95         assert(buff && klen);
  96         ret = klogctl(3, buff, len);
  97         assert(ret >= 0);
  98         *klen = ret;
  99
 100         return buff;
 101 }
 102
 103 static void put_klog_buff(char *buff)
 104 {
 105         free(buff);
 106 }
 107
 108 static int get_last_jit_image(char *haystack, size_t hlen,
 109                               uint8_t *image, size_t ilen)
 110 {
 111         char *ptr, *pptr, *tmp;
 112         off_t off = 0;
 113         int ret, flen, proglen, pass, ulen = 0;
 114         regmatch_t pmatch[1];
 115         unsigned long base;
 116         regex_t regex;
 117
 118         if (hlen == 0)
 119                 return 0;
 120
 121         ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
 122                       "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
 123         assert(ret == 0);
 124
 125         ptr = haystack;
 126         memset(pmatch, 0, sizeof(pmatch));
 127
 128         while (1) {
 129                 ret = regexec(&regex, ptr, 1, pmatch, 0);
 130                 if (ret == 0) {
 131                         ptr += pmatch[0].rm_eo;
 132                         off += pmatch[0].rm_eo;
 133                         assert(off < hlen);
 134                 } else
 135                         break;
 136         }
 137
 138         ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
 139         ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
 140                      &flen, &proglen, &pass, &base);
 141         if (ret != 4)
 142                 return 0;
 143
 144         tmp = ptr = haystack + off;
 145         while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
 146                 tmp = NULL;
 147                 if (!strstr(ptr, "JIT code"))
 148                         continue;
 149                 pptr = ptr;
 150                 while ((ptr = strstr(pptr, ":")))
 151                         pptr = ptr + 1;
 152                 ptr = pptr;
 153                 do {
 154                         image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
 155                         if (ptr == pptr || ulen >= ilen) {
 156                                 ulen--;
 157                                 break;
 158                         }
 159                         ptr = pptr;
 160                 } while (1);
 161         }
 162
 163         assert(ulen == proglen);
 164         printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
 165                proglen, pass, flen);
 166         printf("%lx + <x>:\n", base);
 167
 168         regfree(&regex);
 169         return ulen;
 170 }
 171
 172 int main(int argc, char **argv)
 173 {
 174         int len, klen, opcodes = 0;
 175         char *kbuff;
 176         static uint8_t image[32768];
 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));
 193         if (len > 0)
 194                 get_asm_insns(image, len, opcodes);
 195
 196         put_klog_buff(kbuff);
 197
 198         return 0;
 199 }