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	if (len < 0)
102		return NULL;
103
104	buff = malloc(len);
105	if (!buff)
106		return NULL;
107
108	ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
109	if (ret < 0) {
110		free(buff);
111		return NULL;
112	}
113
114	*klen = ret;
115	return buff;
116}
117
118static char *get_flog_buff(const char *file, unsigned int *klen)
119{
120	int fd, ret, len;
121	struct stat fi;
122	char *buff;
123
124	fd = open(file, O_RDONLY);
125	if (fd < 0)
126		return NULL;
127
128	ret = fstat(fd, &fi);
129	if (ret < 0 || !S_ISREG(fi.st_mode))
130		goto out;
131
132	len = fi.st_size + 1;
133	buff = malloc(len);
134	if (!buff)
135		goto out;
136
137	memset(buff, 0, len);
138	ret = read(fd, buff, len - 1);
139	if (ret <= 0)
140		goto out_free;
141
142	close(fd);
143	*klen = ret;
144	return buff;
145out_free:
146	free(buff);
147out:
148	close(fd);
149	return NULL;
150}
151
152static char *get_log_buff(const char *file, unsigned int *klen)
153{
154	return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
155}
156
157static void put_log_buff(char *buff)
158{
159	free(buff);
160}
161
162static unsigned int get_last_jit_image(char *haystack, size_t hlen,
163				       uint8_t *image, size_t ilen)
164{
165	char *ptr, *pptr, *tmp;
166	off_t off = 0;
167	int ret, flen, proglen, pass, ulen = 0;
168	regmatch_t pmatch[1];
169	unsigned long base;
170	regex_t regex;
171
172	if (hlen == 0)
173		return 0;
174
175	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
176		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
177	assert(ret == 0);
178
179	ptr = haystack;
180	memset(pmatch, 0, sizeof(pmatch));
181
182	while (1) {
183		ret = regexec(&regex, ptr, 1, pmatch, 0);
184		if (ret == 0) {
185			ptr += pmatch[0].rm_eo;
186			off += pmatch[0].rm_eo;
187			assert(off < hlen);
188		} else
189			break;
190	}
191
192	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
193	ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
194		     &flen, &proglen, &pass, &base);
195	if (ret != 4) {
196		regfree(&regex);
197		return 0;
198	}
199
200	tmp = ptr = haystack + off;
201	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
202		tmp = NULL;
203		if (!strstr(ptr, "JIT code"))
204			continue;
205		pptr = ptr;
206		while ((ptr = strstr(pptr, ":")))
207			pptr = ptr + 1;
208		ptr = pptr;
209		do {
210			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
211			if (ptr == pptr || ulen >= ilen) {
212				ulen--;
213				break;
214			}
215			ptr = pptr;
216		} while (1);
217	}
218
219	assert(ulen == proglen);
220	printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
221	       proglen, pass, flen);
222	printf("%lx + <x>:\n", base);
223
224	regfree(&regex);
225	return ulen;
226}
227
228static void usage(void)
229{
230	printf("Usage: bpf_jit_disasm [...]\n");
231	printf("       -o          Also display related opcodes (default: off).\n");
232	printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
233	printf("       -h          Display this help.\n");
234}
235
236int main(int argc, char **argv)
237{
238	unsigned int len, klen, opt, opcodes = 0;
239	static uint8_t image[32768];
240	char *kbuff, *file = NULL;
241
242	while ((opt = getopt(argc, argv, "of:")) != -1) {
243		switch (opt) {
244		case 'o':
245			opcodes = 1;
246			break;
247		case 'f':
248			file = optarg;
249			break;
250		default:
251			usage();
252			return -1;
253		}
254	}
255
256	bfd_init();
257	memset(image, 0, sizeof(image));
258
259	kbuff = get_log_buff(file, &klen);
260	if (!kbuff) {
261		fprintf(stderr, "Could not retrieve log buffer!\n");
262		return -1;
263	}
264
265	len = get_last_jit_image(kbuff, klen, image, sizeof(image));
266	if (len > 0)
267		get_asm_insns(image, len, opcodes);
268	else
269		fprintf(stderr, "No JIT image found!\n");
270
271	put_log_buff(kbuff);
272	return 0;
273}