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
34static 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
51static 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
95static 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	buff = malloc(len);
102	if (!buff)
103		return NULL;
104
105	ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
106	if (ret < 0) {
107		free(buff);
108		return NULL;
109	}
110
111	*klen = ret;
112	return buff;
113}
114
115static char *get_flog_buff(const char *file, unsigned int *klen)
116{
117	int fd, ret, len;
118	struct stat fi;
119	char *buff;
120
121	fd = open(file, O_RDONLY);
122	if (fd < 0)
123		return NULL;
124
125	ret = fstat(fd, &fi);
126	if (ret < 0 || !S_ISREG(fi.st_mode))
127		goto out;
128
129	len = fi.st_size + 1;
130	buff = malloc(len);
131	if (!buff)
132		goto out;
133
134	memset(buff, 0, len);
135	ret = read(fd, buff, len - 1);
136	if (ret <= 0)
137		goto out_free;
138
139	close(fd);
140	*klen = ret;
141	return buff;
142out_free:
143	free(buff);
144out:
145	close(fd);
146	return NULL;
147}
148
149static char *get_log_buff(const char *file, unsigned int *klen)
150{
151	return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
152}
153
154static void put_log_buff(char *buff)
155{
156	free(buff);
157}
158
159static unsigned int get_last_jit_image(char *haystack, size_t hlen,
160				       uint8_t *image, size_t ilen)
161{
162	char *ptr, *pptr, *tmp;
163	off_t off = 0;
164	int ret, flen, proglen, pass, ulen = 0;
165	regmatch_t pmatch[1];
166	unsigned long base;
167	regex_t regex;
168
169	if (hlen == 0)
170		return 0;
171
172	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
173		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
174	assert(ret == 0);
175
176	ptr = haystack;
177	memset(pmatch, 0, sizeof(pmatch));
178
179	while (1) {
180		ret = regexec(&regex, ptr, 1, pmatch, 0);
181		if (ret == 0) {
182			ptr += pmatch[0].rm_eo;
183			off += pmatch[0].rm_eo;
184			assert(off < hlen);
185		} else
186			break;
187	}
188
189	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
190	ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
191		     &flen, &proglen, &pass, &base);
192	if (ret != 4) {
193		regfree(&regex);
194		return 0;
195	}
196
197	tmp = ptr = haystack + off;
198	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
199		tmp = NULL;
200		if (!strstr(ptr, "JIT code"))
201			continue;
202		pptr = ptr;
203		while ((ptr = strstr(pptr, ":")))
204			pptr = ptr + 1;
205		ptr = pptr;
206		do {
207			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
208			if (ptr == pptr || ulen >= ilen) {
209				ulen--;
210				break;
211			}
212			ptr = pptr;
213		} while (1);
214	}
215
216	assert(ulen == proglen);
217	printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
218	       proglen, pass, flen);
219	printf("%lx + <x>:\n", base);
220
221	regfree(&regex);
222	return ulen;
223}
224
225static void usage(void)
226{
227	printf("Usage: bpf_jit_disasm [...]\n");
228	printf("       -o          Also display related opcodes (default: off).\n");
229	printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
230	printf("       -h          Display this help.\n");
231}
232
233int main(int argc, char **argv)
234{
235	unsigned int len, klen, opt, opcodes = 0;
236	static uint8_t image[32768];
237	char *kbuff, *file = NULL;
238
239	while ((opt = getopt(argc, argv, "of:")) != -1) {
240		switch (opt) {
241		case 'o':
242			opcodes = 1;
243			break;
244		case 'f':
245			file = optarg;
246			break;
247		default:
248			usage();
249			return -1;
250		}
251	}
252
253	bfd_init();
254	memset(image, 0, sizeof(image));
255
256	kbuff = get_log_buff(file, &klen);
257	if (!kbuff) {
258		fprintf(stderr, "Could not retrieve log buffer!\n");
259		return -1;
260	}
261
262	len = get_last_jit_image(kbuff, klen, image, sizeof(image));
263	if (len > 0)
264		get_asm_insns(image, len, opcodes);
265	else
266		fprintf(stderr, "No JIT image found!\n");
267
268	put_log_buff(kbuff);
269	return 0;
270}
271