Commit | Line | Data |
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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 | ||
46 | static void get_asm_insns(uint8_t *image, size_t len, unsigned long base, | |
47 | int opcodes) | |
48 | { | |
49 | int count, i, pc = 0; | |
50 | char tpath[256]; | |
51 | struct disassemble_info info; | |
52 | disassembler_ftype disassemble; | |
53 | bfd *bfdf; | |
54 | ||
55 | memset(tpath, 0, sizeof(tpath)); | |
56 | get_exec_path(tpath, sizeof(tpath)); | |
57 | ||
58 | bfdf = bfd_openr(tpath, NULL); | |
59 | assert(bfdf); | |
60 | assert(bfd_check_format(bfdf, bfd_object)); | |
61 | ||
62 | init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf); | |
63 | info.arch = bfd_get_arch(bfdf); | |
64 | info.mach = bfd_get_mach(bfdf); | |
65 | info.buffer = image; | |
66 | info.buffer_length = len; | |
67 | ||
68 | disassemble_init_for_target(&info); | |
69 | ||
70 | disassemble = disassembler(bfdf); | |
71 | assert(disassemble); | |
72 | ||
73 | do { | |
74 | printf("%4x:\t", pc); | |
75 | ||
76 | count = disassemble(pc, &info); | |
77 | ||
78 | if (opcodes) { | |
79 | printf("\n\t"); | |
80 | for (i = 0; i < count; ++i) | |
81 | printf("%02x ", (uint8_t) image[pc + i]); | |
82 | } | |
83 | printf("\n"); | |
84 | ||
85 | pc += count; | |
86 | } while(count > 0 && pc < len); | |
87 | ||
88 | bfd_close(bfdf); | |
89 | } | |
90 | ||
91 | static char *get_klog_buff(int *klen) | |
92 | { | |
93 | int ret, len = klogctl(10, NULL, 0); | |
94 | char *buff = malloc(len); | |
95 | ||
96 | assert(buff && klen); | |
97 | ret = klogctl(3, buff, len); | |
98 | assert(ret >= 0); | |
99 | *klen = ret; | |
100 | ||
101 | return buff; | |
102 | } | |
103 | ||
104 | static void put_klog_buff(char *buff) | |
105 | { | |
106 | free(buff); | |
107 | } | |
108 | ||
109 | static int get_last_jit_image(char *haystack, size_t hlen, | |
110 | uint8_t *image, size_t ilen, | |
111 | unsigned long *base) | |
112 | { | |
113 | char *ptr, *pptr, *tmp; | |
114 | off_t off = 0; | |
115 | int ret, flen, proglen, pass, ulen = 0; | |
116 | regmatch_t pmatch[1]; | |
117 | regex_t regex; | |
118 | ||
119 | if (hlen == 0) | |
120 | return 0; | |
121 | ||
122 | ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ " | |
123 | "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED); | |
124 | assert(ret == 0); | |
125 | ||
126 | ptr = haystack; | |
127 | while (1) { | |
128 | ret = regexec(®ex, ptr, 1, pmatch, 0); | |
129 | if (ret == 0) { | |
130 | ptr += pmatch[0].rm_eo; | |
131 | off += pmatch[0].rm_eo; | |
132 | assert(off < hlen); | |
133 | } else | |
134 | break; | |
135 | } | |
136 | ||
137 | ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so); | |
138 | ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx", | |
139 | &flen, &proglen, &pass, base); | |
140 | if (ret != 4) | |
141 | return 0; | |
142 | ||
143 | tmp = ptr = haystack + off; | |
144 | while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) { | |
145 | tmp = NULL; | |
146 | if (!strstr(ptr, "JIT code")) | |
147 | continue; | |
148 | pptr = ptr; | |
149 | while ((ptr = strstr(pptr, ":"))) | |
150 | pptr = ptr + 1; | |
151 | ptr = pptr; | |
152 | do { | |
153 | image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16); | |
154 | if (ptr == pptr || ulen >= ilen) { | |
155 | ulen--; | |
156 | break; | |
157 | } | |
158 | ptr = pptr; | |
159 | } while (1); | |
160 | } | |
161 | ||
162 | assert(ulen == proglen); | |
163 | printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n", | |
164 | proglen, pass, flen); | |
165 | printf("%lx + <x>:\n", *base); | |
166 | ||
167 | regfree(®ex); | |
168 | return ulen; | |
169 | } | |
170 | ||
171 | int main(int argc, char **argv) | |
172 | { | |
173 | int len, klen, opcodes = 0; | |
174 | char *kbuff; | |
175 | unsigned long base; | |
176 | uint8_t image[4096]; | |
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), &base); | |
193 | if (len > 0 && base > 0) | |
194 | get_asm_insns(image, len, base, opcodes); | |
195 | ||
196 | put_klog_buff(kbuff); | |
197 | ||
198 | return 0; | |
199 | } |