tools/bpf/bpf_jit_disasm.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Minimal BPF JIT image disassembler
   4  *
   5  * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
   6  * debugging or verification purposes.
   7  *
   8  * To get the disassembly of the JIT code, do the following:
   9  *
  10  *  1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
  11  *  2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
  12  *  3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
  13  *
  14  * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
  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 #include <limits.h>
  31 #include <tools/dis-asm-compat.h>
  32
  33 #define CMD_ACTION_SIZE_BUFFER          10
  34 #define CMD_ACTION_READ_ALL             3
  35
  36 static void get_exec_path(char *tpath, size_t size)
  37 {
  38         char *path;
  39         ssize_t len;
  40
  41         snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
  42         tpath[size - 1] = 0;
  43
  44         path = strdup(tpath);
  45         assert(path);
  46
  47         len = readlink(path, tpath, size);
  48         tpath[len] = 0;
  49
  50         free(path);
  51 }
  52
  53 static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
  54 {
  55         int count, i, pc = 0;
  56         char tpath[PATH_MAX];
  57         struct disassemble_info info;
  58         disassembler_ftype disassemble;
  59         bfd *bfdf;
  60
  61         memset(tpath, 0, sizeof(tpath));
  62         get_exec_path(tpath, sizeof(tpath));
  63
  64         bfdf = bfd_openr(tpath, NULL);
  65         assert(bfdf);
  66         assert(bfd_check_format(bfdf, bfd_object));
  67
  68         init_disassemble_info_compat(&info, stdout,
  69                                      (fprintf_ftype) fprintf,
  70                                      fprintf_styled);
  71         info.arch = bfd_get_arch(bfdf);
  72         info.mach = bfd_get_mach(bfdf);
  73         info.buffer = image;
  74         info.buffer_length = len;
  75
  76         disassemble_init_for_target(&info);
  77
  78 #ifdef DISASM_FOUR_ARGS_SIGNATURE
  79         disassemble = disassembler(info.arch,
  80                                    bfd_big_endian(bfdf),
  81                                    info.mach,
  82                                    bfdf);
  83 #else
  84         disassemble = disassembler(bfdf);
  85 #endif
  86         assert(disassemble);
  87
  88         do {
  89                 printf("%4x:\t", pc);
  90
  91                 count = disassemble(pc, &info);
  92
  93                 if (opcodes) {
  94                         printf("\n\t");
  95                         for (i = 0; i < count; ++i)
  96                                 printf("%02x ", (uint8_t) image[pc + i]);
  97                 }
  98                 printf("\n");
  99
 100                 pc += count;
 101         } while(count > 0 && pc < len);
 102
 103         bfd_close(bfdf);
 104 }
 105
 106 static char *get_klog_buff(unsigned int *klen)
 107 {
 108         int ret, len;
 109         char *buff;
 110
 111         len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
 112         if (len < 0)
 113                 return NULL;
 114
 115         buff = malloc(len);
 116         if (!buff)
 117                 return NULL;
 118
 119         ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
 120         if (ret < 0) {
 121                 free(buff);
 122                 return NULL;
 123         }
 124
 125         *klen = ret;
 126         return buff;
 127 }
 128
 129 static char *get_flog_buff(const char *file, unsigned int *klen)
 130 {
 131         int fd, ret, len;
 132         struct stat fi;
 133         char *buff;
 134
 135         fd = open(file, O_RDONLY);
 136         if (fd < 0)
 137                 return NULL;
 138
 139         ret = fstat(fd, &fi);
 140         if (ret < 0 || !S_ISREG(fi.st_mode))
 141                 goto out;
 142
 143         len = fi.st_size + 1;
 144         buff = malloc(len);
 145         if (!buff)
 146                 goto out;
 147
 148         memset(buff, 0, len);
 149         ret = read(fd, buff, len - 1);
 150         if (ret <= 0)
 151                 goto out_free;
 152
 153         close(fd);
 154         *klen = ret;
 155         return buff;
 156 out_free:
 157         free(buff);
 158 out:
 159         close(fd);
 160         return NULL;
 161 }
 162
 163 static char *get_log_buff(const char *file, unsigned int *klen)
 164 {
 165         return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
 166 }
 167
 168 static void put_log_buff(char *buff)
 169 {
 170         free(buff);
 171 }
 172
 173 static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
 174                                    unsigned int *ilen)
 175 {
 176         char *ptr, *pptr, *tmp;
 177         off_t off = 0;
 178         unsigned int proglen;
 179         int ret, flen, pass, ulen = 0;
 180         regmatch_t pmatch[1];
 181         unsigned long base;
 182         regex_t regex;
 183         uint8_t *image;
 184
 185         if (hlen == 0)
 186                 return NULL;
 187
 188         ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
 189                       "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
 190         assert(ret == 0);
 191
 192         ptr = haystack;
 193         memset(pmatch, 0, sizeof(pmatch));
 194
 195         while (1) {
 196                 ret = regexec(&regex, ptr, 1, pmatch, 0);
 197                 if (ret == 0) {
 198                         ptr += pmatch[0].rm_eo;
 199                         off += pmatch[0].rm_eo;
 200                         assert(off < hlen);
 201                 } else
 202                         break;
 203         }
 204
 205         ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
 206         ret = sscanf(ptr, "flen=%d proglen=%u pass=%d image=%lx",
 207                      &flen, &proglen, &pass, &base);
 208         if (ret != 4) {
 209                 regfree(&regex);
 210                 return NULL;
 211         }
 212         if (proglen > 1000000) {
 213                 printf("proglen of %u too big, stopping\n", proglen);
 214                 return NULL;
 215         }
 216
 217         image = malloc(proglen);
 218         if (!image) {
 219                 printf("Out of memory\n");
 220                 return NULL;
 221         }
 222         memset(image, 0, proglen);
 223
 224         tmp = ptr = haystack + off;
 225         while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
 226                 tmp = NULL;
 227                 if (!strstr(ptr, "JIT code"))
 228                         continue;
 229                 pptr = ptr;
 230                 while ((ptr = strstr(pptr, ":")))
 231                         pptr = ptr + 1;
 232                 ptr = pptr;
 233                 do {
 234                         image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
 235                         if (ptr == pptr) {
 236                                 ulen--;
 237                                 break;
 238                         }
 239                         if (ulen >= proglen)
 240                                 break;
 241                         ptr = pptr;
 242                 } while (1);
 243         }
 244
 245         assert(ulen == proglen);
 246         printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
 247                proglen, pass, flen);
 248         printf("%lx + <x>:\n", base);
 249
 250         regfree(&regex);
 251         *ilen = ulen;
 252         return image;
 253 }
 254
 255 static void usage(void)
 256 {
 257         printf("Usage: bpf_jit_disasm [...]\n");
 258         printf("       -o          Also display related opcodes (default: off).\n");
 259         printf("       -O <file>   Write binary image of code to file, don't disassemble to stdout.\n");
 260         printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
 261         printf("       -h          Display this help.\n");
 262 }
 263
 264 int main(int argc, char **argv)
 265 {
 266         unsigned int len, klen, opt, opcodes = 0;
 267         char *kbuff, *file = NULL;
 268         char *ofile = NULL;
 269         int ofd;
 270         ssize_t nr;
 271         uint8_t *pos;
 272         uint8_t *image = NULL;
 273
 274         while ((opt = getopt(argc, argv, "of:O:")) != -1) {
 275                 switch (opt) {
 276                 case 'o':
 277                         opcodes = 1;
 278                         break;
 279                 case 'O':
 280                         ofile = optarg;
 281                         break;
 282                 case 'f':
 283                         file = optarg;
 284                         break;
 285                 default:
 286                         usage();
 287                         return -1;
 288                 }
 289         }
 290
 291         bfd_init();
 292
 293         kbuff = get_log_buff(file, &klen);
 294         if (!kbuff) {
 295                 fprintf(stderr, "Could not retrieve log buffer!\n");
 296                 return -1;
 297         }
 298
 299         image = get_last_jit_image(kbuff, klen, &len);
 300         if (!image) {
 301                 fprintf(stderr, "No JIT image found!\n");
 302                 goto done;
 303         }
 304         if (!ofile) {
 305                 get_asm_insns(image, len, opcodes);
 306                 goto done;
 307         }
 308
 309         ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
 310         if (ofd < 0) {
 311                 fprintf(stderr, "Could not open file %s for writing: ", ofile);
 312                 perror(NULL);
 313                 goto done;
 314         }
 315         pos = image;
 316         do {
 317                 nr = write(ofd, pos, len);
 318                 if (nr < 0) {
 319                         fprintf(stderr, "Could not write data to %s: ", ofile);
 320                         perror(NULL);
 321                         goto done;
 322                 }
 323                 len -= nr;
 324                 pos += nr;
 325         } while (len);
 326         close(ofd);
 327
 328 done:
 329         put_log_buff(kbuff);
 330         free(image);
 331         return 0;
 332 }