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 <regex.h>
  26 #include <fcntl.h>
  27 #include <sys/klog.h>
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30
  31 #define CMD_ACTION_SIZE_BUFFER          10
  32 #define CMD_ACTION_READ_ALL             3
  33
  34 static void get_exec_path(char *tpath, size_t size)
  35 {
  36         char *path;
  37         ssize_t len;
  38
  39         snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
  40         tpath[size - 1] = 0;
  41
  42         path = strdup(tpath);
  43         assert(path);
  44
  45         len = readlink(path, tpath, size);
  46         tpath[len] = 0;
  47
  48         free(path);
  49 }
  50
  51 static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
  52 {
  53         int count, i, pc = 0;
  54         char tpath[256];
  55         struct disassemble_info info;
  56         disassembler_ftype disassemble;
  57         bfd *bfdf;
  58
  59         memset(tpath, 0, sizeof(tpath));
  60         get_exec_path(tpath, sizeof(tpath));
  61
  62         bfdf = bfd_openr(tpath, NULL);
  63         assert(bfdf);
  64         assert(bfd_check_format(bfdf, bfd_object));
  65
  66         init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
  67         info.arch = bfd_get_arch(bfdf);
  68         info.mach = bfd_get_mach(bfdf);
  69         info.buffer = image;
  70         info.buffer_length = len;
  71
  72         disassemble_init_for_target(&info);
  73
  74         disassemble = disassembler(bfdf);
  75         assert(disassemble);
  76
  77         do {
  78                 printf("%4x:\t", pc);
  79
  80                 count = disassemble(pc, &info);
  81
  82                 if (opcodes) {
  83                         printf("\n\t");
  84                         for (i = 0; i < count; ++i)
  85                                 printf("%02x ", (uint8_t) image[pc + i]);
  86                 }
  87                 printf("\n");
  88
  89                 pc += count;
  90         } while(count > 0 && pc < len);
  91
  92         bfd_close(bfdf);
  93 }
  94
  95 static char *get_klog_buff(unsigned int *klen)
  96 {
  97         int ret, len;
  98         char *buff;
  99
 100         len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
 101         if (len < 0)
 102                 return NULL;
 103
 104         buff = malloc(len);
 105         if (!buff)
 106                 return NULL;
 107
 108         ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
 109         if (ret < 0) {
 110                 free(buff);
 111                 return NULL;
 112         }
 113
 114         *klen = ret;
 115         return buff;
 116 }
 117
 118 static char *get_flog_buff(const char *file, unsigned int *klen)
 119 {
 120         int fd, ret, len;
 121         struct stat fi;
 122         char *buff;
 123
 124         fd = open(file, O_RDONLY);
 125         if (fd < 0)
 126                 return NULL;
 127
 128         ret = fstat(fd, &fi);
 129         if (ret < 0 || !S_ISREG(fi.st_mode))
 130                 goto out;
 131
 132         len = fi.st_size + 1;
 133         buff = malloc(len);
 134         if (!buff)
 135                 goto out;
 136
 137         memset(buff, 0, len);
 138         ret = read(fd, buff, len - 1);
 139         if (ret <= 0)
 140                 goto out_free;
 141
 142         close(fd);
 143         *klen = ret;
 144         return buff;
 145 out_free:
 146         free(buff);
 147 out:
 148         close(fd);
 149         return NULL;
 150 }
 151
 152 static char *get_log_buff(const char *file, unsigned int *klen)
 153 {
 154         return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
 155 }
 156
 157 static void put_log_buff(char *buff)
 158 {
 159         free(buff);
 160 }
 161
 162 static unsigned int get_last_jit_image(char *haystack, size_t hlen,
 163                                        uint8_t *image, size_t ilen)
 164 {
 165         char *ptr, *pptr, *tmp;
 166         off_t off = 0;
 167         int ret, flen, proglen, pass, ulen = 0;
 168         regmatch_t pmatch[1];
 169         unsigned long base;
 170         regex_t regex;
 171
 172         if (hlen == 0)
 173                 return 0;
 174
 175         ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
 176                       "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
 177         assert(ret == 0);
 178
 179         ptr = haystack;
 180         memset(pmatch, 0, sizeof(pmatch));
 181
 182         while (1) {
 183                 ret = regexec(&regex, ptr, 1, pmatch, 0);
 184                 if (ret == 0) {
 185                         ptr += pmatch[0].rm_eo;
 186                         off += pmatch[0].rm_eo;
 187                         assert(off < hlen);
 188                 } else
 189                         break;
 190         }
 191
 192         ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
 193         ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
 194                      &flen, &proglen, &pass, &base);
 195         if (ret != 4) {
 196                 regfree(&regex);
 197                 return 0;
 198         }
 199
 200         tmp = ptr = haystack + off;
 201         while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
 202                 tmp = NULL;
 203                 if (!strstr(ptr, "JIT code"))
 204                         continue;
 205                 pptr = ptr;
 206                 while ((ptr = strstr(pptr, ":")))
 207                         pptr = ptr + 1;
 208                 ptr = pptr;
 209                 do {
 210                         image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
 211                         if (ptr == pptr || ulen >= ilen) {
 212                                 ulen--;
 213                                 break;
 214                         }
 215                         ptr = pptr;
 216                 } while (1);
 217         }
 218
 219         assert(ulen == proglen);
 220         printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
 221                proglen, pass, flen);
 222         printf("%lx + <x>:\n", base);
 223
 224         regfree(&regex);
 225         return ulen;
 226 }
 227
 228 static void usage(void)
 229 {
 230         printf("Usage: bpf_jit_disasm [...]\n");
 231         printf("       -o          Also display related opcodes (default: off).\n");
 232         printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
 233         printf("       -h          Display this help.\n");
 234 }
 235
 236 int main(int argc, char **argv)
 237 {
 238         unsigned int len, klen, opt, opcodes = 0;
 239         static uint8_t image[32768];
 240         char *kbuff, *file = NULL;
 241
 242         while ((opt = getopt(argc, argv, "of:")) != -1) {
 243                 switch (opt) {
 244                 case 'o':
 245                         opcodes = 1;
 246                         break;
 247                 case 'f':
 248                         file = optarg;
 249                         break;
 250                 default:
 251                         usage();
 252                         return -1;
 253                 }
 254         }
 255
 256         bfd_init();
 257         memset(image, 0, sizeof(image));
 258
 259         kbuff = get_log_buff(file, &klen);
 260         if (!kbuff) {
 261                 fprintf(stderr, "Could not retrieve log buffer!\n");
 262                 return -1;
 263         }
 264
 265         len = get_last_jit_image(kbuff, klen, image, sizeof(image));
 266         if (len > 0)
 267                 get_asm_insns(image, len, opcodes);
 268         else
 269                 fprintf(stderr, "No JIT image found!\n");
 270
 271         put_log_buff(kbuff);
 272         return 0;
 273 }