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
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	tpath[len] = 0;
49
50	free(path);
51}
52
53static 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
106static 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
129static 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;
156out_free:
157	free(buff);
158out:
159	close(fd);
160	return NULL;
161}
162
163static 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
168static void put_log_buff(char *buff)
169{
170	free(buff);
171}
172
173static 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
255static 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
264int 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
328done:
329	put_log_buff(kbuff);
330	free(image);
331	return 0;
332}
333