/* * Minimal BPF JIT image disassembler * * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for * debugging or verification purposes. * * To get the disassembly of the JIT code, do the following: * * 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable` * 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`) * 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code * * Copyright 2013 Daniel Borkmann * Licensed under the GNU General Public License, version 2.0 (GPLv2) */ #include #include #include #include #include #include #include #include #include #include #include #include #include #define CMD_ACTION_SIZE_BUFFER 10 #define CMD_ACTION_READ_ALL 3 static void get_exec_path(char *tpath, size_t size) { char *path; ssize_t len; snprintf(tpath, size, "/proc/%d/exe", (int) getpid()); tpath[size - 1] = 0; path = strdup(tpath); assert(path); len = readlink(path, tpath, size); tpath[len] = 0; free(path); } static void get_asm_insns(uint8_t *image, size_t len, int opcodes) { int count, i, pc = 0; char tpath[256]; struct disassemble_info info; disassembler_ftype disassemble; bfd *bfdf; memset(tpath, 0, sizeof(tpath)); get_exec_path(tpath, sizeof(tpath)); bfdf = bfd_openr(tpath, NULL); assert(bfdf); assert(bfd_check_format(bfdf, bfd_object)); init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf); info.arch = bfd_get_arch(bfdf); info.mach = bfd_get_mach(bfdf); info.buffer = image; info.buffer_length = len; disassemble_init_for_target(&info); disassemble = disassembler(bfdf); assert(disassemble); do { printf("%4x:\t", pc); count = disassemble(pc, &info); if (opcodes) { printf("\n\t"); for (i = 0; i < count; ++i) printf("%02x ", (uint8_t) image[pc + i]); } printf("\n"); pc += count; } while(count > 0 && pc < len); bfd_close(bfdf); } static char *get_klog_buff(unsigned int *klen) { int ret, len; char *buff; len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0); if (len < 0) return NULL; buff = malloc(len); if (!buff) return NULL; ret = klogctl(CMD_ACTION_READ_ALL, buff, len); if (ret < 0) { free(buff); return NULL; } *klen = ret; return buff; } static char *get_flog_buff(const char *file, unsigned int *klen) { int fd, ret, len; struct stat fi; char *buff; fd = open(file, O_RDONLY); if (fd < 0) return NULL; ret = fstat(fd, &fi); if (ret < 0 || !S_ISREG(fi.st_mode)) goto out; len = fi.st_size + 1; buff = malloc(len); if (!buff) goto out; memset(buff, 0, len); ret = read(fd, buff, len - 1); if (ret <= 0) goto out_free; close(fd); *klen = ret; return buff; out_free: free(buff); out: close(fd); return NULL; } static char *get_log_buff(const char *file, unsigned int *klen) { return file ? get_flog_buff(file, klen) : get_klog_buff(klen); } static void put_log_buff(char *buff) { free(buff); } static uint8_t *get_last_jit_image(char *haystack, size_t hlen, unsigned int *ilen) { char *ptr, *pptr, *tmp; off_t off = 0; int ret, flen, proglen, pass, ulen = 0; regmatch_t pmatch[1]; unsigned long base; regex_t regex; uint8_t *image; if (hlen == 0) return NULL; ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ " "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED); assert(ret == 0); ptr = haystack; memset(pmatch, 0, sizeof(pmatch)); while (1) { ret = regexec(®ex, ptr, 1, pmatch, 0); if (ret == 0) { ptr += pmatch[0].rm_eo; off += pmatch[0].rm_eo; assert(off < hlen); } else break; } ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so); ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx", &flen, &proglen, &pass, &base); if (ret != 4) { regfree(®ex); return NULL; } if (proglen > 1000000) { printf("proglen of %d too big, stopping\n", proglen); return NULL; } image = malloc(proglen); if (!image) { printf("Out of memory\n"); return NULL; } memset(image, 0, proglen); tmp = ptr = haystack + off; while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) { tmp = NULL; if (!strstr(ptr, "JIT code")) continue; pptr = ptr; while ((ptr = strstr(pptr, ":"))) pptr = ptr + 1; ptr = pptr; do { image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16); if (ptr == pptr) { ulen--; break; } if (ulen >= proglen) break; ptr = pptr; } while (1); } assert(ulen == proglen); printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n", proglen, pass, flen); printf("%lx + :\n", base); regfree(®ex); *ilen = ulen; return image; } static void usage(void) { printf("Usage: bpf_jit_disasm [...]\n"); printf(" -o Also display related opcodes (default: off).\n"); printf(" -O Write binary image of code to file, don't disassemble to stdout.\n"); printf(" -f Read last image dump from file or stdin (default: klog).\n"); printf(" -h Display this help.\n"); } int main(int argc, char **argv) { unsigned int len, klen, opt, opcodes = 0; char *kbuff, *file = NULL; char *ofile = NULL; int ofd; ssize_t nr; uint8_t *pos; uint8_t *image = NULL; while ((opt = getopt(argc, argv, "of:O:")) != -1) { switch (opt) { case 'o': opcodes = 1; break; case 'O': ofile = optarg; break; case 'f': file = optarg; break; default: usage(); return -1; } } bfd_init(); kbuff = get_log_buff(file, &klen); if (!kbuff) { fprintf(stderr, "Could not retrieve log buffer!\n"); return -1; } image = get_last_jit_image(kbuff, klen, &len); if (!image) { fprintf(stderr, "No JIT image found!\n"); goto done; } if (!ofile) { get_asm_insns(image, len, opcodes); goto done; } ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE); if (ofd < 0) { fprintf(stderr, "Could not open file %s for writing: ", ofile); perror(NULL); goto done; } pos = image; do { nr = write(ofd, pos, len); if (nr < 0) { fprintf(stderr, "Could not write data to %s: ", ofile); perror(NULL); goto done; } len -= nr; pos += nr; } while (len); close(ofd); done: put_log_buff(kbuff); free(image); return 0; }