bpf_jit_disasm.c

  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	if (len < 0)
 49		len = 0;
 50	tpath[len] = 0;
 51
 52	free(path);
 53}
 54
 55static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
 56{
 57	int count, i, pc = 0;
 58	char tpath[PATH_MAX];
 59	struct disassemble_info info;
 60	disassembler_ftype disassemble;
 61	bfd *bfdf;
 62
 63	memset(tpath, 0, sizeof(tpath));
 64	get_exec_path(tpath, sizeof(tpath));
 65
 66	bfdf = bfd_openr(tpath, NULL);
 67	assert(bfdf);
 68	assert(bfd_check_format(bfdf, bfd_object));
 69
 70	init_disassemble_info_compat(&info, stdout,
 71				     (fprintf_ftype) fprintf,
 72				     fprintf_styled);
 73	info.arch = bfd_get_arch(bfdf);
 74	info.mach = bfd_get_mach(bfdf);
 75	info.buffer = image;
 76	info.buffer_length = len;
 77
 78	disassemble_init_for_target(&info);
 79
 80#ifdef DISASM_FOUR_ARGS_SIGNATURE
 81	disassemble = disassembler(info.arch,
 82				   bfd_big_endian(bfdf),
 83				   info.mach,
 84				   bfdf);
 85#else
 86	disassemble = disassembler(bfdf);
 87#endif
 88	assert(disassemble);
 89
 90	do {
 91		printf("%4x:\t", pc);
 92
 93		count = disassemble(pc, &info);
 94
 95		if (opcodes) {
 96			printf("\n\t");
 97			for (i = 0; i < count; ++i)
 98				printf("%02x ", (uint8_t) image[pc + i]);
 99		}
100		printf("\n");
101
102		pc += count;
103	} while(count > 0 && pc < len);
104
105	bfd_close(bfdf);
106}
107
108static char *get_klog_buff(unsigned int *klen)
109{
110	int ret, len;
111	char *buff;
112
113	len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
114	if (len < 0)
115		return NULL;
116
117	buff = malloc(len);
118	if (!buff)
119		return NULL;
120
121	ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
122	if (ret < 0) {
123		free(buff);
124		return NULL;
125	}
126
127	*klen = ret;
128	return buff;
129}
130
131static char *get_flog_buff(const char *file, unsigned int *klen)
132{
133	int fd, ret, len;
134	struct stat fi;
135	char *buff;
136
137	fd = open(file, O_RDONLY);
138	if (fd < 0)
139		return NULL;
140
141	ret = fstat(fd, &fi);
142	if (ret < 0 || !S_ISREG(fi.st_mode))
143		goto out;
144
145	len = fi.st_size + 1;
146	buff = malloc(len);
147	if (!buff)
148		goto out;
149
150	memset(buff, 0, len);
151	ret = read(fd, buff, len - 1);
152	if (ret <= 0)
153		goto out_free;
154
155	close(fd);
156	*klen = ret;
157	return buff;
158out_free:
159	free(buff);
160out:
161	close(fd);
162	return NULL;
163}
164
165static char *get_log_buff(const char *file, unsigned int *klen)
166{
167	return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
168}
169
170static void put_log_buff(char *buff)
171{
172	free(buff);
173}
174
175static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
176				   unsigned int *ilen)
177{
178	char *ptr, *pptr, *tmp;
179	off_t off = 0;
180	unsigned int proglen;
181	int ret, flen, pass, ulen = 0;
182	regmatch_t pmatch[1];
183	unsigned long base;
184	regex_t regex;
185	uint8_t *image;
186
187	if (hlen == 0)
188		return NULL;
189
190	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
191		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
192	assert(ret == 0);
193
194	ptr = haystack;
195	memset(pmatch, 0, sizeof(pmatch));
196
197	while (1) {
198		ret = regexec(&regex, ptr, 1, pmatch, 0);
199		if (ret == 0) {
200			ptr += pmatch[0].rm_eo;
201			off += pmatch[0].rm_eo;
202			assert(off < hlen);
203		} else
204			break;
205	}
206
207	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
208	ret = sscanf(ptr, "flen=%d proglen=%u pass=%d image=%lx",
209		     &flen, &proglen, &pass, &base);
210	if (ret != 4) {
211		regfree(&regex);
212		return NULL;
213	}
214	if (proglen > 1000000) {
215		printf("proglen of %u too big, stopping\n", proglen);
216		return NULL;
217	}
218
219	image = malloc(proglen);
220	if (!image) {
221		printf("Out of memory\n");
222		return NULL;
223	}
224	memset(image, 0, proglen);
225
226	tmp = ptr = haystack + off;
227	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
228		tmp = NULL;
229		if (!strstr(ptr, "JIT code"))
230			continue;
231		pptr = ptr;
232		while ((ptr = strstr(pptr, ":")))
233			pptr = ptr + 1;
234		ptr = pptr;
235		do {
236			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
237			if (ptr == pptr) {
238				ulen--;
239				break;
240			}
241			if (ulen >= proglen)
242				break;
243			ptr = pptr;
244		} while (1);
245	}
246
247	assert(ulen == proglen);
248	printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
249	       proglen, pass, flen);
250	printf("%lx + <x>:\n", base);
251
252	regfree(&regex);
253	*ilen = ulen;
254	return image;
255}
256
257static void usage(void)
258{
259	printf("Usage: bpf_jit_disasm [...]\n");
260	printf("       -o          Also display related opcodes (default: off).\n");
261	printf("       -O <file>   Write binary image of code to file, don't disassemble to stdout.\n");
262	printf("       -f <file>   Read last image dump from file or stdin (default: klog).\n");
263	printf("       -h          Display this help.\n");
264}
265
266int main(int argc, char **argv)
267{
268	unsigned int len, klen, opt, opcodes = 0;
269	char *kbuff, *file = NULL;
270	char *ofile = NULL;
271	int ofd;
272	ssize_t nr;
273	uint8_t *pos;
274	uint8_t *image = NULL;
275
276	while ((opt = getopt(argc, argv, "of:O:")) != -1) {
277		switch (opt) {
278		case 'o':
279			opcodes = 1;
280			break;
281		case 'O':
282			ofile = optarg;
283			break;
284		case 'f':
285			file = optarg;
286			break;
287		default:
288			usage();
289			return -1;
290		}
291	}
292
293	bfd_init();
294
295	kbuff = get_log_buff(file, &klen);
296	if (!kbuff) {
297		fprintf(stderr, "Could not retrieve log buffer!\n");
298		return -1;
299	}
300
301	image = get_last_jit_image(kbuff, klen, &len);
302	if (!image) {
303		fprintf(stderr, "No JIT image found!\n");
304		goto done;
305	}
306	if (!ofile) {
307		get_asm_insns(image, len, opcodes);
308		goto done;
309	}
310
311	ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
312	if (ofd < 0) {
313		fprintf(stderr, "Could not open file %s for writing: ", ofile);
314		perror(NULL);
315		goto done;
316	}
317	pos = image;
318	do {
319		nr = write(ofd, pos, len);
320		if (nr < 0) {
321			fprintf(stderr, "Could not write data to %s: ", ofile);
322			perror(NULL);
323			goto done;
324		}
325		len -= nr;
326		pos += nr;
327	} while (len);
328	close(ofd);
329
330done:
331	put_log_buff(kbuff);
332	free(image);
333	return 0;
334}