Commit | Line | Data |
---|---|---|
e306e2c1 DB |
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 | ||
29 | static 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 | ||
ed4afd45 | 46 | static void get_asm_insns(uint8_t *image, size_t len, int opcodes) |
e306e2c1 DB |
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 | ||
90 | static 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 | ||
103 | static void put_klog_buff(char *buff) | |
104 | { | |
105 | free(buff); | |
106 | } | |
107 | ||
108 | static int get_last_jit_image(char *haystack, size_t hlen, | |
ed4afd45 | 109 | uint8_t *image, size_t ilen) |
e306e2c1 DB |
110 | { |
111 | char *ptr, *pptr, *tmp; | |
112 | off_t off = 0; | |
113 | int ret, flen, proglen, pass, ulen = 0; | |
114 | regmatch_t pmatch[1]; | |
ed4afd45 | 115 | unsigned long base; |
e306e2c1 DB |
116 | regex_t regex; |
117 | ||
118 | if (hlen == 0) | |
119 | return 0; | |
120 | ||
121 | ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ " | |
122 | "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED); | |
123 | assert(ret == 0); | |
124 | ||
125 | ptr = haystack; | |
082739aa DB |
126 | memset(pmatch, 0, sizeof(pmatch)); |
127 | ||
e306e2c1 DB |
128 | while (1) { |
129 | ret = regexec(®ex, 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", | |
ed4afd45 | 140 | &flen, &proglen, &pass, &base); |
e306e2c1 DB |
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); | |
ed4afd45 | 166 | printf("%lx + <x>:\n", base); |
e306e2c1 DB |
167 | |
168 | regfree(®ex); | |
169 | return ulen; | |
170 | } | |
171 | ||
172 | int main(int argc, char **argv) | |
173 | { | |
174 | int len, klen, opcodes = 0; | |
175 | char *kbuff; | |
9bb1a208 | 176 | static uint8_t image[32768]; |
e306e2c1 DB |
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 | ||
ed4afd45 AS |
192 | len = get_last_jit_image(kbuff, klen, image, sizeof(image)); |
193 | if (len > 0) | |
194 | get_asm_insns(image, len, opcodes); | |
e306e2c1 DB |
195 | |
196 | put_klog_buff(kbuff); | |
197 | ||
198 | return 0; | |
199 | } |