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 <sys/klog.h>
26#include <sys/types.h>
27#include <regex.h>
28
29static void get_exec_path(char *tpath, size_t size)
30{
31	char *path;
32	ssize_t len;
33
34	snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
35	tpath[size - 1] = 0;
36
37	path = strdup(tpath);
38	assert(path);
39
40	len = readlink(path, tpath, size);
41	tpath[len] = 0;
42
43	free(path);
44}
45
46static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
47{
48	int count, i, pc = 0;
49	char tpath[256];
50	struct disassemble_info info;
51	disassembler_ftype disassemble;
52	bfd *bfdf;
53
54	memset(tpath, 0, sizeof(tpath));
55	get_exec_path(tpath, sizeof(tpath));
56
57	bfdf = bfd_openr(tpath, NULL);
58	assert(bfdf);
59	assert(bfd_check_format(bfdf, bfd_object));
60
61	init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
62	info.arch = bfd_get_arch(bfdf);
63	info.mach = bfd_get_mach(bfdf);
64	info.buffer = image;
65	info.buffer_length = len;
66
67	disassemble_init_for_target(&info);
68
69	disassemble = disassembler(bfdf);
70	assert(disassemble);
71
72	do {
73		printf("%4x:\t", pc);
74
75		count = disassemble(pc, &info);
76
77		if (opcodes) {
78			printf("\n\t");
79			for (i = 0; i < count; ++i)
80				printf("%02x ", (uint8_t) image[pc + i]);
81		}
82		printf("\n");
83
84		pc += count;
85	} while(count > 0 && pc < len);
86
87	bfd_close(bfdf);
88}
89
90static char *get_klog_buff(int *klen)
91{
92	int ret, len = klogctl(10, NULL, 0);
93	char *buff = malloc(len);
94
95	assert(buff && klen);
96	ret = klogctl(3, buff, len);
97	assert(ret >= 0);
98	*klen = ret;
99
100	return buff;
101}
102
103static void put_klog_buff(char *buff)
104{
105	free(buff);
106}
107
108static int get_last_jit_image(char *haystack, size_t hlen,
109			      uint8_t *image, size_t ilen)
110{
111	char *ptr, *pptr, *tmp;
112	off_t off = 0;
113	int ret, flen, proglen, pass, ulen = 0;
114	regmatch_t pmatch[1];
115	unsigned long base;
116	regex_t regex;
117
118	if (hlen == 0)
119		return 0;
120
121	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
122		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
123	assert(ret == 0);
124
125	ptr = haystack;
126	memset(pmatch, 0, sizeof(pmatch));
127
128	while (1) {
129		ret = regexec(&regex, ptr, 1, pmatch, 0);
130		if (ret == 0) {
131			ptr += pmatch[0].rm_eo;
132			off += pmatch[0].rm_eo;
133			assert(off < hlen);
134		} else
135			break;
136	}
137
138	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
139	ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
140		     &flen, &proglen, &pass, &base);
141	if (ret != 4)
142		return 0;
143
144	tmp = ptr = haystack + off;
145	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
146		tmp = NULL;
147		if (!strstr(ptr, "JIT code"))
148			continue;
149		pptr = ptr;
150		while ((ptr = strstr(pptr, ":")))
151			pptr = ptr + 1;
152		ptr = pptr;
153		do {
154			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
155			if (ptr == pptr || ulen >= ilen) {
156				ulen--;
157				break;
158			}
159			ptr = pptr;
160		} while (1);
161	}
162
163	assert(ulen == proglen);
164	printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
165	       proglen, pass, flen);
166	printf("%lx + <x>:\n", base);
167
168	regfree(&regex);
169	return ulen;
170}
171
172int main(int argc, char **argv)
173{
174	int len, klen, opcodes = 0;
175	char *kbuff;
176	static uint8_t image[32768];
177
178	if (argc > 1) {
179		if (!strncmp("-o", argv[argc - 1], 2)) {
180			opcodes = 1;
181		} else {
182			printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
183			exit(0);
184		}
185	}
186
187	bfd_init();
188	memset(image, 0, sizeof(image));
189
190	kbuff = get_klog_buff(&klen);
191
192	len = get_last_jit_image(kbuff, klen, image, sizeof(image));
193	if (len > 0)
194		get_asm_insns(image, len, opcodes);
195
196	put_klog_buff(kbuff);
197
198	return 0;
199}
200