xref: /linux/tools/bpf/bpf_jit_disasm.c (revision be239684b18e1cdcafcf8c7face4a2f562c745ad) 
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 <borkmann@redhat.com>
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 
36 static 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 	tpath[len] = 0;
49 
50 	free(path);
51 }
52 
53 static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
54 {
55 	int count, i, pc = 0;
56 	char tpath[PATH_MAX];
57 	struct disassemble_info info;
58 	disassembler_ftype disassemble;
59 	bfd *bfdf;
60 
61 	memset(tpath, 0, sizeof(tpath));
62 	get_exec_path(tpath, sizeof(tpath));
63 
64 	bfdf = bfd_openr(tpath, NULL);
65 	assert(bfdf);
66 	assert(bfd_check_format(bfdf, bfd_object));
67 
68 	init_disassemble_info_compat(&info, stdout,
69 				     (fprintf_ftype) fprintf,
70 				     fprintf_styled);
71 	info.arch = bfd_get_arch(bfdf);
72 	info.mach = bfd_get_mach(bfdf);
73 	info.buffer = image;
74 	info.buffer_length = len;
75 
76 	disassemble_init_for_target(&info);
77 
78 #ifdef DISASM_FOUR_ARGS_SIGNATURE
79 	disassemble = disassembler(info.arch,
80 				   bfd_big_endian(bfdf),
81 				   info.mach,
82 				   bfdf);
83 #else
84 	disassemble = disassembler(bfdf);
85 #endif
86 	assert(disassemble);
87 
88 	do {
89 		printf("%4x:\t", pc);
90 
91 		count = disassemble(pc, &info);
92 
93 		if (opcodes) {
94 			printf("\n\t");
95 			for (i = 0; i < count; ++i)
96 				printf("%02x ", (uint8_t) image[pc + i]);
97 		}
98 		printf("\n");
99 
100 		pc += count;
101 	} while(count > 0 && pc < len);
102 
103 	bfd_close(bfdf);
104 }
105 
106 static char *get_klog_buff(unsigned int *klen)
107 {
108 	int ret, len;
109 	char *buff;
110 
111 	len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
112 	if (len < 0)
113 		return NULL;
114 
115 	buff = malloc(len);
116 	if (!buff)
117 		return NULL;
118 
119 	ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
120 	if (ret < 0) {
121 		free(buff);
122 		return NULL;
123 	}
124 
125 	*klen = ret;
126 	return buff;
127 }
128 
129 static char *get_flog_buff(const char *file, unsigned int *klen)
130 {
131 	int fd, ret, len;
132 	struct stat fi;
133 	char *buff;
134 
135 	fd = open(file, O_RDONLY);
136 	if (fd < 0)
137 		return NULL;
138 
139 	ret = fstat(fd, &fi);
140 	if (ret < 0 || !S_ISREG(fi.st_mode))
141 		goto out;
142 
143 	len = fi.st_size + 1;
144 	buff = malloc(len);
145 	if (!buff)
146 		goto out;
147 
148 	memset(buff, 0, len);
149 	ret = read(fd, buff, len - 1);
150 	if (ret <= 0)
151 		goto out_free;
152 
153 	close(fd);
154 	*klen = ret;
155 	return buff;
156 out_free:
157 	free(buff);
158 out:
159 	close(fd);
160 	return NULL;
161 }
162 
163 static char *get_log_buff(const char *file, unsigned int *klen)
164 {
165 	return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
166 }
167 
168 static void put_log_buff(char *buff)
169 {
170 	free(buff);
171 }
172 
173 static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
174 				   unsigned int *ilen)
175 {
176 	char *ptr, *pptr, *tmp;
177 	off_t off = 0;
178 	unsigned int proglen;
179 	int ret, flen, pass, ulen = 0;
180 	regmatch_t pmatch[1];
181 	unsigned long base;
182 	regex_t regex;
183 	uint8_t *image;
184 
185 	if (hlen == 0)
186 		return NULL;
187 
188 	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
189 		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
190 	assert(ret == 0);
191 
192 	ptr = haystack;
193 	memset(pmatch, 0, sizeof(pmatch));
194 
195 	while (1) {
196 		ret = regexec(&regex, ptr, 1, pmatch, 0);
197 		if (ret == 0) {
198 			ptr += pmatch[0].rm_eo;
199 			off += pmatch[0].rm_eo;
200 			assert(off < hlen);
201 		} else
202 			break;
203 	}
204 
205 	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
206 	ret = sscanf(ptr, "flen=%d proglen=%u pass=%d image=%lx",
207 		     &flen, &proglen, &pass, &base);
208 	if (ret != 4) {
209 		regfree(&regex);
210 		return NULL;
211 	}
212 	if (proglen > 1000000) {
213 		printf("proglen of %d too big, stopping\n", proglen);
214 		return NULL;
215 	}
216 
217 	image = malloc(proglen);
218 	if (!image) {
219 		printf("Out of memory\n");
220 		return NULL;
221 	}
222 	memset(image, 0, proglen);
223 
224 	tmp = ptr = haystack + off;
225 	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
226 		tmp = NULL;
227 		if (!strstr(ptr, "JIT code"))
228 			continue;
229 		pptr = ptr;
230 		while ((ptr = strstr(pptr, ":")))
231 			pptr = ptr + 1;
232 		ptr = pptr;
233 		do {
234 			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
235 			if (ptr == pptr) {
236 				ulen--;
237 				break;
238 			}
239 			if (ulen >= proglen)
240 				break;
241 			ptr = pptr;
242 		} while (1);
243 	}
244 
245 	assert(ulen == proglen);
246 	printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
247 	       proglen, pass, flen);
248 	printf("%lx + <x>:\n", base);
249 
250 	regfree(&regex);
251 	*ilen = ulen;
252 	return image;
253 }
254 
255 static void usage(void)
256 {
257 	printf("Usage: bpf_jit_disasm [...]\n");
258 	printf("       -o          Also display related opcodes (default: off).\n");
259 	printf("       -O <file>   Write binary image of code to file, don't disassemble to stdout.\n");
260 	printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
261 	printf("       -h          Display this help.\n");
262 }
263 
264 int main(int argc, char **argv)
265 {
266 	unsigned int len, klen, opt, opcodes = 0;
267 	char *kbuff, *file = NULL;
268 	char *ofile = NULL;
269 	int ofd;
270 	ssize_t nr;
271 	uint8_t *pos;
272 	uint8_t *image = NULL;
273 
274 	while ((opt = getopt(argc, argv, "of:O:")) != -1) {
275 		switch (opt) {
276 		case 'o':
277 			opcodes = 1;
278 			break;
279 		case 'O':
280 			ofile = optarg;
281 			break;
282 		case 'f':
283 			file = optarg;
284 			break;
285 		default:
286 			usage();
287 			return -1;
288 		}
289 	}
290 
291 	bfd_init();
292 
293 	kbuff = get_log_buff(file, &klen);
294 	if (!kbuff) {
295 		fprintf(stderr, "Could not retrieve log buffer!\n");
296 		return -1;
297 	}
298 
299 	image = get_last_jit_image(kbuff, klen, &len);
300 	if (!image) {
301 		fprintf(stderr, "No JIT image found!\n");
302 		goto done;
303 	}
304 	if (!ofile) {
305 		get_asm_insns(image, len, opcodes);
306 		goto done;
307 	}
308 
309 	ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
310 	if (ofd < 0) {
311 		fprintf(stderr, "Could not open file %s for writing: ", ofile);
312 		perror(NULL);
313 		goto done;
314 	}
315 	pos = image;
316 	do {
317 		nr = write(ofd, pos, len);
318 		if (nr < 0) {
319 			fprintf(stderr, "Could not write data to %s: ", ofile);
320 			perror(NULL);
321 			goto done;
322 		}
323 		len -= nr;
324 		pos += nr;
325 	} while (len);
326 	close(ofd);
327 
328 done:
329 	put_log_buff(kbuff);
330 	free(image);
331 	return 0;
332 }
333