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/*
* Minimal BPF JIT image disassembler
*
* Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
* debugging or verification purposes.
*
* There is no Makefile. Compile with
*
* `gcc -Wall -O2 bpf_jit_disasm.c -o bpf_jit_disasm -lopcodes -lbfd -ldl`
*
* or similar.
*
* To get the disassembly of the JIT code, do the following:
*
* 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
* 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
* 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
*
* Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
* Licensed under the GNU General Public License, version 2.0 (GPLv2)
*
* Note: this is part of the Linux kernel and can be found under tools/net/.
*/
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <bfd.h>
#include <dis-asm.h>
#include <sys/klog.h>
#include <sys/types.h>
#include <regex.h>
static void get_exec_path(char *tpath, size_t size)
{
char *path;
ssize_t len;
snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
tpath[size - 1] = 0;
path = strdup(tpath);
assert(path);
len = readlink(path, tpath, size);
tpath[len] = 0;
free(path);
}
static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
int opcodes)
{
int count, i, pc = 0;
char tpath[256];
struct disassemble_info info;
disassembler_ftype disassemble;
bfd *bfdf;
memset(tpath, 0, sizeof(tpath));
get_exec_path(tpath, sizeof(tpath));
bfdf = bfd_openr(tpath, NULL);
assert(bfdf);
assert(bfd_check_format(bfdf, bfd_object));
init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
info.arch = bfd_get_arch(bfdf);
info.mach = bfd_get_mach(bfdf);
info.buffer = image;
info.buffer_length = len;
disassemble_init_for_target(&info);
disassemble = disassembler(bfdf);
assert(disassemble);
do {
printf("%4x:\t", pc);
count = disassemble(pc, &info);
if (opcodes) {
printf("\n\t");
for (i = 0; i < count; ++i)
printf("%02x ", (uint8_t) image[pc + i]);
}
printf("\n");
pc += count;
} while(count > 0 && pc < len);
bfd_close(bfdf);
}
static char *get_klog_buff(int *klen)
{
int ret, len = klogctl(10, NULL, 0);
char *buff = malloc(len);
assert(buff && klen);
ret = klogctl(3, buff, len);
assert(ret >= 0);
*klen = ret;
return buff;
}
static void put_klog_buff(char *buff)
{
free(buff);
}
static int get_last_jit_image(char *haystack, size_t hlen,
uint8_t *image, size_t ilen,
unsigned long *base)
{
char *ptr, *pptr, *tmp;
off_t off = 0;
int ret, flen, proglen, pass, ulen = 0;
regmatch_t pmatch[1];
regex_t regex;
if (hlen == 0)
return 0;
ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
"pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
assert(ret == 0);
ptr = haystack;
while (1) {
ret = regexec(®ex, ptr, 1, pmatch, 0);
if (ret == 0) {
ptr += pmatch[0].rm_eo;
off += pmatch[0].rm_eo;
assert(off < hlen);
} else
break;
}
ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
&flen, &proglen, &pass, base);
if (ret != 4)
return 0;
tmp = ptr = haystack + off;
while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
tmp = NULL;
if (!strstr(ptr, "JIT code"))
continue;
pptr = ptr;
while ((ptr = strstr(pptr, ":")))
pptr = ptr + 1;
ptr = pptr;
do {
image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
if (ptr == pptr || ulen >= ilen) {
ulen--;
break;
}
ptr = pptr;
} while (1);
}
assert(ulen == proglen);
printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
proglen, pass, flen);
printf("%lx + <x>:\n", *base);
regfree(®ex);
return ulen;
}
int main(int argc, char **argv)
{
int len, klen, opcodes = 0;
char *kbuff;
unsigned long base;
uint8_t image[4096];
if (argc > 1) {
if (!strncmp("-o", argv[argc - 1], 2)) {
opcodes = 1;
} else {
printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
exit(0);
}
}
bfd_init();
memset(image, 0, sizeof(image));
kbuff = get_klog_buff(&klen);
len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
if (len > 0 && base > 0)
get_asm_insns(image, len, base, opcodes);
put_klog_buff(kbuff);
return 0;
}
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