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