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
34 static 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
51 static 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
95 static 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
118 static 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;
145 out_free:
146 free(buff);
147 out:
148 close(fd);
149 return NULL;
150 }
151
152 static 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
157 static void put_log_buff(char *buff)
158 {
159 free(buff);
160 }
161
162 static 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(®ex, "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(®ex, 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(®ex);
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(®ex);
225 return ulen;
226 }
227
228 static 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
236 int 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 }
274
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