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Linux/tools/bpf/bpf_jit_disasm.c

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  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 #ifdef DISASM_FOUR_ARGS_SIGNATURE
 76         disassemble = disassembler(info.arch,
 77                                    bfd_big_endian(bfdf),
 78                                    info.mach,
 79                                    bfdf);
 80 #else
 81         disassemble = disassembler(bfdf);
 82 #endif
 83         assert(disassemble);
 84 
 85         do {
 86                 printf("%4x:\t", pc);
 87 
 88                 count = disassemble(pc, &info);
 89 
 90                 if (opcodes) {
 91                         printf("\n\t");
 92                         for (i = 0; i < count; ++i)
 93                                 printf("%02x ", (uint8_t) image[pc + i]);
 94                 }
 95                 printf("\n");
 96 
 97                 pc += count;
 98         } while(count > 0 && pc < len);
 99 
100         bfd_close(bfdf);
101 }
102 
103 static char *get_klog_buff(unsigned int *klen)
104 {
105         int ret, len;
106         char *buff;
107 
108         len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
109         if (len < 0)
110                 return NULL;
111 
112         buff = malloc(len);
113         if (!buff)
114                 return NULL;
115 
116         ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
117         if (ret < 0) {
118                 free(buff);
119                 return NULL;
120         }
121 
122         *klen = ret;
123         return buff;
124 }
125 
126 static char *get_flog_buff(const char *file, unsigned int *klen)
127 {
128         int fd, ret, len;
129         struct stat fi;
130         char *buff;
131 
132         fd = open(file, O_RDONLY);
133         if (fd < 0)
134                 return NULL;
135 
136         ret = fstat(fd, &fi);
137         if (ret < 0 || !S_ISREG(fi.st_mode))
138                 goto out;
139 
140         len = fi.st_size + 1;
141         buff = malloc(len);
142         if (!buff)
143                 goto out;
144 
145         memset(buff, 0, len);
146         ret = read(fd, buff, len - 1);
147         if (ret <= 0)
148                 goto out_free;
149 
150         close(fd);
151         *klen = ret;
152         return buff;
153 out_free:
154         free(buff);
155 out:
156         close(fd);
157         return NULL;
158 }
159 
160 static char *get_log_buff(const char *file, unsigned int *klen)
161 {
162         return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
163 }
164 
165 static void put_log_buff(char *buff)
166 {
167         free(buff);
168 }
169 
170 static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
171                                    unsigned int *ilen)
172 {
173         char *ptr, *pptr, *tmp;
174         off_t off = 0;
175         unsigned int proglen;
176         int ret, flen, pass, ulen = 0;
177         regmatch_t pmatch[1];
178         unsigned long base;
179         regex_t regex;
180         uint8_t *image;
181 
182         if (hlen == 0)
183                 return NULL;
184 
185         ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
186                       "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
187         assert(ret == 0);
188 
189         ptr = haystack;
190         memset(pmatch, 0, sizeof(pmatch));
191 
192         while (1) {
193                 ret = regexec(&regex, ptr, 1, pmatch, 0);
194                 if (ret == 0) {
195                         ptr += pmatch[0].rm_eo;
196                         off += pmatch[0].rm_eo;
197                         assert(off < hlen);
198                 } else
199                         break;
200         }
201 
202         ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
203         ret = sscanf(ptr, "flen=%d proglen=%u pass=%d image=%lx",
204                      &flen, &proglen, &pass, &base);
205         if (ret != 4) {
206                 regfree(&regex);
207                 return NULL;
208         }
209         if (proglen > 1000000) {
210                 printf("proglen of %d too big, stopping\n", proglen);
211                 return NULL;
212         }
213 
214         image = malloc(proglen);
215         if (!image) {
216                 printf("Out of memory\n");
217                 return NULL;
218         }
219         memset(image, 0, proglen);
220 
221         tmp = ptr = haystack + off;
222         while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
223                 tmp = NULL;
224                 if (!strstr(ptr, "JIT code"))
225                         continue;
226                 pptr = ptr;
227                 while ((ptr = strstr(pptr, ":")))
228                         pptr = ptr + 1;
229                 ptr = pptr;
230                 do {
231                         image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
232                         if (ptr == pptr) {
233                                 ulen--;
234                                 break;
235                         }
236                         if (ulen >= proglen)
237                                 break;
238                         ptr = pptr;
239                 } while (1);
240         }
241 
242         assert(ulen == proglen);
243         printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
244                proglen, pass, flen);
245         printf("%lx + <x>:\n", base);
246 
247         regfree(&regex);
248         *ilen = ulen;
249         return image;
250 }
251 
252 static void usage(void)
253 {
254         printf("Usage: bpf_jit_disasm [...]\n");
255         printf("       -o          Also display related opcodes (default: off).\n");
256         printf("       -O <file>   Write binary image of code to file, don't disassemble to stdout.\n");
257         printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
258         printf("       -h          Display this help.\n");
259 }
260 
261 int main(int argc, char **argv)
262 {
263         unsigned int len, klen, opt, opcodes = 0;
264         char *kbuff, *file = NULL;
265         char *ofile = NULL;
266         int ofd;
267         ssize_t nr;
268         uint8_t *pos;
269         uint8_t *image = NULL;
270 
271         while ((opt = getopt(argc, argv, "of:O:")) != -1) {
272                 switch (opt) {
273                 case 'o':
274                         opcodes = 1;
275                         break;
276                 case 'O':
277                         ofile = optarg;
278                         break;
279                 case 'f':
280                         file = optarg;
281                         break;
282                 default:
283                         usage();
284                         return -1;
285                 }
286         }
287 
288         bfd_init();
289 
290         kbuff = get_log_buff(file, &klen);
291         if (!kbuff) {
292                 fprintf(stderr, "Could not retrieve log buffer!\n");
293                 return -1;
294         }
295 
296         image = get_last_jit_image(kbuff, klen, &len);
297         if (!image) {
298                 fprintf(stderr, "No JIT image found!\n");
299                 goto done;
300         }
301         if (!ofile) {
302                 get_asm_insns(image, len, opcodes);
303                 goto done;
304         }
305 
306         ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
307         if (ofd < 0) {
308                 fprintf(stderr, "Could not open file %s for writing: ", ofile);
309                 perror(NULL);
310                 goto done;
311         }
312         pos = image;
313         do {
314                 nr = write(ofd, pos, len);
315                 if (nr < 0) {
316                         fprintf(stderr, "Could not write data to %s: ", ofile);
317                         perror(NULL);
318                         goto done;
319                 }
320                 len -= nr;
321                 pos += nr;
322         } while (len);
323         close(ofd);
324 
325 done:
326         put_log_buff(kbuff);
327         free(image);
328         return 0;
329 }
330 

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