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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 <[email protected]>
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
36static 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 if (len < 0)
49 len = 0;
50 tpath[len] = 0;
51
52 free(path);
53}
54
55static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
56{
57 int count, i, pc = 0;
58 char tpath[PATH_MAX];
59 struct disassemble_info info;
60 disassembler_ftype disassemble;
61 bfd *bfdf;
62
63 memset(tpath, 0, sizeof(tpath));
64 get_exec_path(tpath, sizeof(tpath));
65
66 bfdf = bfd_openr(tpath, NULL);
67 assert(bfdf);
68 assert(bfd_check_format(bfdf, bfd_object));
69
70 init_disassemble_info_compat(&info, stdout,
71 (fprintf_ftype) fprintf,
72 fprintf_styled);
73 info.arch = bfd_get_arch(bfdf);
74 info.mach = bfd_get_mach(bfdf);
75 info.buffer = image;
76 info.buffer_length = len;
77
78 disassemble_init_for_target(&info);
79
80#ifdef DISASM_FOUR_ARGS_SIGNATURE
81 disassemble = disassembler(info.arch,
82 bfd_big_endian(bfdf),
83 info.mach,
84 bfdf);
85#else
86 disassemble = disassembler(bfdf);
87#endif
88 assert(disassemble);
89
90 do {
91 printf("%4x:\t", pc);
92
93 count = disassemble(pc, &info);
94
95 if (opcodes) {
96 printf("\n\t");
97 for (i = 0; i < count; ++i)
98 printf("%02x ", (uint8_t) image[pc + i]);
99 }
100 printf("\n");
101
102 pc += count;
103 } while(count > 0 && pc < len);
104
105 bfd_close(bfdf);
106}
107
108static char *get_klog_buff(unsigned int *klen)
109{
110 int ret, len;
111 char *buff;
112
113 len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
114 if (len < 0)
115 return NULL;
116
117 buff = malloc(len);
118 if (!buff)
119 return NULL;
120
121 ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
122 if (ret < 0) {
123 free(buff);
124 return NULL;
125 }
126
127 *klen = ret;
128 return buff;
129}
130
131static char *get_flog_buff(const char *file, unsigned int *klen)
132{
133 int fd, ret, len;
134 struct stat fi;
135 char *buff;
136
137 fd = open(file, O_RDONLY);
138 if (fd < 0)
139 return NULL;
140
141 ret = fstat(fd, &fi);
142 if (ret < 0 || !S_ISREG(fi.st_mode))
143 goto out;
144
145 len = fi.st_size + 1;
146 buff = malloc(len);
147 if (!buff)
148 goto out;
149
150 memset(buff, 0, len);
151 ret = read(fd, buff, len - 1);
152 if (ret <= 0)
153 goto out_free;
154
155 close(fd);
156 *klen = ret;
157 return buff;
158out_free:
159 free(buff);
160out:
161 close(fd);
162 return NULL;
163}
164
165static char *get_log_buff(const char *file, unsigned int *klen)
166{
167 return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
168}
169
170static void put_log_buff(char *buff)
171{
172 free(buff);
173}
174
175static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
176 unsigned int *ilen)
177{
178 char *ptr, *pptr, *tmp;
179 off_t off = 0;
180 unsigned int proglen;
181 int ret, flen, pass, ulen = 0;
182 regmatch_t pmatch[1];
183 unsigned long base;
184 regex_t regex;
185 uint8_t *image;
186
187 if (hlen == 0)
188 return NULL;
189
190 ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
191 "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
192 assert(ret == 0);
193
194 ptr = haystack;
195 memset(pmatch, 0, sizeof(pmatch));
196
197 while (1) {
198 ret = regexec(&regex, ptr, 1, pmatch, 0);
199 if (ret == 0) {
200 ptr += pmatch[0].rm_eo;
201 off += pmatch[0].rm_eo;
202 assert(off < hlen);
203 } else
204 break;
205 }
206
207 ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
208 ret = sscanf(ptr, "flen=%d proglen=%u pass=%d image=%lx",
209 &flen, &proglen, &pass, &base);
210 if (ret != 4) {
211 regfree(&regex);
212 return NULL;
213 }
214 if (proglen > 1000000) {
215 printf("proglen of %u too big, stopping\n", proglen);
216 return NULL;
217 }
218
219 image = malloc(proglen);
220 if (!image) {
221 printf("Out of memory\n");
222 return NULL;
223 }
224 memset(image, 0, proglen);
225
226 tmp = ptr = haystack + off;
227 while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
228 tmp = NULL;
229 if (!strstr(ptr, "JIT code"))
230 continue;
231 pptr = ptr;
232 while ((ptr = strstr(pptr, ":")))
233 pptr = ptr + 1;
234 ptr = pptr;
235 do {
236 image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
237 if (ptr == pptr) {
238 ulen--;
239 break;
240 }
241 if (ulen >= proglen)
242 break;
243 ptr = pptr;
244 } while (1);
245 }
246
247 assert(ulen == proglen);
248 printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
249 proglen, pass, flen);
250 printf("%lx + <x>:\n", base);
251
252 regfree(&regex);
253 *ilen = ulen;
254 return image;
255}
256
257static void usage(void)
258{
259 printf("Usage: bpf_jit_disasm [...]\n");
260 printf(" -o Also display related opcodes (default: off).\n");
261 printf(" -O <file> Write binary image of code to file, don't disassemble to stdout.\n");
262 printf(" -f <file> Read last image dump from file or stdin (default: klog).\n");
263 printf(" -h Display this help.\n");
264}
265
266int main(int argc, char **argv)
267{
268 unsigned int len, klen, opt, opcodes = 0;
269 char *kbuff, *file = NULL;
270 char *ofile = NULL;
271 int ofd;
272 ssize_t nr;
273 uint8_t *pos;
274 uint8_t *image = NULL;
275
276 while ((opt = getopt(argc, argv, "of:O:")) != -1) {
277 switch (opt) {
278 case 'o':
279 opcodes = 1;
280 break;
281 case 'O':
282 ofile = optarg;
283 break;
284 case 'f':
285 file = optarg;
286 break;
287 default:
288 usage();
289 return -1;
290 }
291 }
292
293 bfd_init();
294
295 kbuff = get_log_buff(file, &klen);
296 if (!kbuff) {
297 fprintf(stderr, "Could not retrieve log buffer!\n");
298 return -1;
299 }
300
301 image = get_last_jit_image(kbuff, klen, &len);
302 if (!image) {
303 fprintf(stderr, "No JIT image found!\n");
304 goto done;
305 }
306 if (!ofile) {
307 get_asm_insns(image, len, opcodes);
308 goto done;
309 }
310
311 ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
312 if (ofd < 0) {
313 fprintf(stderr, "Could not open file %s for writing: ", ofile);
314 perror(NULL);
315 goto done;
316 }
317 pos = image;
318 do {
319 nr = write(ofd, pos, len);
320 if (nr < 0) {
321 fprintf(stderr, "Could not write data to %s: ", ofile);
322 perror(NULL);
323 goto done;
324 }
325 len -= nr;
326 pos += nr;
327 } while (len);
328 close(ofd);
329
330done:
331 put_log_buff(kbuff);
332 free(image);
333 return 0;
334}