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
 32#define CMD_ACTION_SIZE_BUFFER		10
 33#define CMD_ACTION_READ_ALL		3
 34
 35static 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
 52static 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
103static 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
126static 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;
153out_free:
154	free(buff);
155out:
156	close(fd);
157	return NULL;
158}
159
160static 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
165static void put_log_buff(char *buff)
166{
167	free(buff);
168}
169
170static 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
252static 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
261int 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
325done:
326	put_log_buff(kbuff);
327	free(image);
328	return 0;
329}