xref: /linux/tools/bpf/bpf_jit_disasm.c (revision 83a37b3292f4aca799b355179ad6fbdd78a08e10) 
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 
31 #define CMD_ACTION_SIZE_BUFFER		10
32 #define CMD_ACTION_READ_ALL		3
33 
34 static void get_exec_path(char *tpath, size_t size)
35 {
36 	char *path;
37 	ssize_t len;
38 
39 	snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
40 	tpath[size - 1] = 0;
41 
42 	path = strdup(tpath);
43 	assert(path);
44 
45 	len = readlink(path, tpath, size);
46 	tpath[len] = 0;
47 
48 	free(path);
49 }
50 
51 static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
52 {
53 	int count, i, pc = 0;
54 	char tpath[256];
55 	struct disassemble_info info;
56 	disassembler_ftype disassemble;
57 	bfd *bfdf;
58 
59 	memset(tpath, 0, sizeof(tpath));
60 	get_exec_path(tpath, sizeof(tpath));
61 
62 	bfdf = bfd_openr(tpath, NULL);
63 	assert(bfdf);
64 	assert(bfd_check_format(bfdf, bfd_object));
65 
66 	init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
67 	info.arch = bfd_get_arch(bfdf);
68 	info.mach = bfd_get_mach(bfdf);
69 	info.buffer = image;
70 	info.buffer_length = len;
71 
72 	disassemble_init_for_target(&info);
73 
74 	disassemble = disassembler(bfdf);
75 	assert(disassemble);
76 
77 	do {
78 		printf("%4x:\t", pc);
79 
80 		count = disassemble(pc, &info);
81 
82 		if (opcodes) {
83 			printf("\n\t");
84 			for (i = 0; i < count; ++i)
85 				printf("%02x ", (uint8_t) image[pc + i]);
86 		}
87 		printf("\n");
88 
89 		pc += count;
90 	} while(count > 0 && pc < len);
91 
92 	bfd_close(bfdf);
93 }
94 
95 static char *get_klog_buff(unsigned int *klen)
96 {
97 	int ret, len;
98 	char *buff;
99 
100 	len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
101 	if (len < 0)
102 		return NULL;
103 
104 	buff = malloc(len);
105 	if (!buff)
106 		return NULL;
107 
108 	ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
109 	if (ret < 0) {
110 		free(buff);
111 		return NULL;
112 	}
113 
114 	*klen = ret;
115 	return buff;
116 }
117 
118 static char *get_flog_buff(const char *file, unsigned int *klen)
119 {
120 	int fd, ret, len;
121 	struct stat fi;
122 	char *buff;
123 
124 	fd = open(file, O_RDONLY);
125 	if (fd < 0)
126 		return NULL;
127 
128 	ret = fstat(fd, &fi);
129 	if (ret < 0 || !S_ISREG(fi.st_mode))
130 		goto out;
131 
132 	len = fi.st_size + 1;
133 	buff = malloc(len);
134 	if (!buff)
135 		goto out;
136 
137 	memset(buff, 0, len);
138 	ret = read(fd, buff, len - 1);
139 	if (ret <= 0)
140 		goto out_free;
141 
142 	close(fd);
143 	*klen = ret;
144 	return buff;
145 out_free:
146 	free(buff);
147 out:
148 	close(fd);
149 	return NULL;
150 }
151 
152 static char *get_log_buff(const char *file, unsigned int *klen)
153 {
154 	return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
155 }
156 
157 static void put_log_buff(char *buff)
158 {
159 	free(buff);
160 }
161 
162 static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
163 				   unsigned int *ilen)
164 {
165 	char *ptr, *pptr, *tmp;
166 	off_t off = 0;
167 	int ret, flen, proglen, pass, ulen = 0;
168 	regmatch_t pmatch[1];
169 	unsigned long base;
170 	regex_t regex;
171 	uint8_t *image;
172 
173 	if (hlen == 0)
174 		return NULL;
175 
176 	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
177 		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
178 	assert(ret == 0);
179 
180 	ptr = haystack;
181 	memset(pmatch, 0, sizeof(pmatch));
182 
183 	while (1) {
184 		ret = regexec(&regex, ptr, 1, pmatch, 0);
185 		if (ret == 0) {
186 			ptr += pmatch[0].rm_eo;
187 			off += pmatch[0].rm_eo;
188 			assert(off < hlen);
189 		} else
190 			break;
191 	}
192 
193 	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
194 	ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
195 		     &flen, &proglen, &pass, &base);
196 	if (ret != 4) {
197 		regfree(&regex);
198 		return NULL;
199 	}
200 	if (proglen > 1000000) {
201 		printf("proglen of %d too big, stopping\n", proglen);
202 		return NULL;
203 	}
204 
205 	image = malloc(proglen);
206 	if (!image) {
207 		printf("Out of memory\n");
208 		return NULL;
209 	}
210 	memset(image, 0, proglen);
211 
212 	tmp = ptr = haystack + off;
213 	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
214 		tmp = NULL;
215 		if (!strstr(ptr, "JIT code"))
216 			continue;
217 		pptr = ptr;
218 		while ((ptr = strstr(pptr, ":")))
219 			pptr = ptr + 1;
220 		ptr = pptr;
221 		do {
222 			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
223 			if (ptr == pptr) {
224 				ulen--;
225 				break;
226 			}
227 			if (ulen >= proglen)
228 				break;
229 			ptr = pptr;
230 		} while (1);
231 	}
232 
233 	assert(ulen == proglen);
234 	printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
235 	       proglen, pass, flen);
236 	printf("%lx + <x>:\n", base);
237 
238 	regfree(&regex);
239 	*ilen = ulen;
240 	return image;
241 }
242 
243 static void usage(void)
244 {
245 	printf("Usage: bpf_jit_disasm [...]\n");
246 	printf("       -o          Also display related opcodes (default: off).\n");
247 	printf("       -O <file>   Write binary image of code to file, don't disassemble to stdout.\n");
248 	printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
249 	printf("       -h          Display this help.\n");
250 }
251 
252 int main(int argc, char **argv)
253 {
254 	unsigned int len, klen, opt, opcodes = 0;
255 	char *kbuff, *file = NULL;
256 	char *ofile = NULL;
257 	int ofd;
258 	ssize_t nr;
259 	uint8_t *pos;
260 	uint8_t *image = NULL;
261 
262 	while ((opt = getopt(argc, argv, "of:O:")) != -1) {
263 		switch (opt) {
264 		case 'o':
265 			opcodes = 1;
266 			break;
267 		case 'O':
268 			ofile = optarg;
269 			break;
270 		case 'f':
271 			file = optarg;
272 			break;
273 		default:
274 			usage();
275 			return -1;
276 		}
277 	}
278 
279 	bfd_init();
280 
281 	kbuff = get_log_buff(file, &klen);
282 	if (!kbuff) {
283 		fprintf(stderr, "Could not retrieve log buffer!\n");
284 		return -1;
285 	}
286 
287 	image = get_last_jit_image(kbuff, klen, &len);
288 	if (!image) {
289 		fprintf(stderr, "No JIT image found!\n");
290 		goto done;
291 	}
292 	if (!ofile) {
293 		get_asm_insns(image, len, opcodes);
294 		goto done;
295 	}
296 
297 	ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
298 	if (ofd < 0) {
299 		fprintf(stderr, "Could not open file %s for writing: ", ofile);
300 		perror(NULL);
301 		goto done;
302 	}
303 	pos = image;
304 	do {
305 		nr = write(ofd, pos, len);
306 		if (nr < 0) {
307 			fprintf(stderr, "Could not write data to %s: ", ofile);
308 			perror(NULL);
309 			goto done;
310 		}
311 		len -= nr;
312 		pos += nr;
313 	} while (len);
314 	close(ofd);
315 
316 done:
317 	put_log_buff(kbuff);
318 	free(image);
319 	return 0;
320 }
321