// SPDX-License-Identifier: GPL-2.0-only
/*
* Minimal BPF JIT image disassembler
*
* Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
* debugging or verification purposes.
*
* 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 <[email protected]>
*/
#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 <regex.h>
#include <fcntl.h>
#include <sys/klog.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <limits.h>
#include <tools/dis-asm-compat.h>
#define CMD_ACTION_SIZE_BUFFER 10
#define CMD_ACTION_READ_ALL 3
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, int opcodes)
{
int count, i, pc = 0;
char tpath[PATH_MAX];
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_compat(&info, stdout,
(fprintf_ftype) fprintf,
fprintf_styled);
info.arch = bfd_get_arch(bfdf);
info.mach = bfd_get_mach(bfdf);
info.buffer = image;
info.buffer_length = len;
disassemble_init_for_target(&info);
#ifdef DISASM_FOUR_ARGS_SIGNATURE
disassemble = disassembler(info.arch,
bfd_big_endian(bfdf),
info.mach,
bfdf);
#else
disassemble = disassembler(bfdf);
#endif
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(unsigned int *klen)
{
int ret, len;
char *buff;
len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
if (len < 0)
return NULL;
buff = malloc(len);
if (!buff)
return NULL;
ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
if (ret < 0) {
free(buff);
return NULL;
}
*klen = ret;
return buff;
}
static char *get_flog_buff(const char *file, unsigned int *klen)
{
int fd, ret, len;
struct stat fi;
char *buff;
fd = open(file, O_RDONLY);
if (fd < 0)
return NULL;
ret = fstat(fd, &fi);
if (ret < 0 || !S_ISREG(fi.st_mode))
goto out;
len = fi.st_size + 1;
buff = malloc(len);
if (!buff)
goto out;
memset(buff, 0, len);
ret = read(fd, buff, len - 1);
if (ret <= 0)
goto out_free;
close(fd);
*klen = ret;
return buff;
out_free:
free(buff);
out:
close(fd);
return NULL;
}
static char *get_log_buff(const char *file, unsigned int *klen)
{
return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
}
static void put_log_buff(char *buff)
{
free(buff);
}
static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
unsigned int *ilen)
{
char *ptr, *pptr, *tmp;
off_t off = 0;
unsigned int proglen;
int ret, flen, pass, ulen = 0;
regmatch_t pmatch[1];
unsigned long base;
regex_t regex;
uint8_t *image;
if (hlen == 0)
return NULL;
ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
"pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
assert(ret == 0);
ptr = haystack;
memset(pmatch, 0, sizeof(pmatch));
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=%u pass=%d image=%lx",
&flen, &proglen, &pass, &base);
if (ret != 4) {
regfree(®ex);
return NULL;
}
if (proglen > 1000000) {
printf("proglen of %d too big, stopping\n", proglen);
return NULL;
}
image = malloc(proglen);
if (!image) {
printf("Out of memory\n");
return NULL;
}
memset(image, 0, proglen);
tmp = ptr = haystack + off;
while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
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--;
break;
}
if (ulen >= proglen)
break;
ptr = pptr;
} while (1);
}
assert(ulen == proglen);
printf("%u bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
proglen, pass, flen);
printf("%lx + <x>:\n", base);
regfree(®ex);
*ilen = ulen;
return image;
}
static void usage(void)
{
printf("Usage: bpf_jit_disasm [...]\n");
printf(" -o Also display related opcodes (default: off).\n");
printf(" -O <file> Write binary image of code to file, don't disassemble to stdout.\n");
printf(" -f <file> Read last image dump from file or stdin (default: klog).\n");
printf(" -h Display this help.\n");
}
int main(int argc, char **argv)
{
unsigned int len, klen, opt, opcodes = 0;
char *kbuff, *file = NULL;
char *ofile = NULL;
int ofd;
ssize_t nr;
uint8_t *pos;
uint8_t *image = NULL;
while ((opt = getopt(argc, argv, "of:O:")) != -1) {
switch (opt) {
case 'o':
opcodes = 1;
break;
case 'O':
ofile = optarg;
break;
case 'f':
file = optarg;
break;
default:
usage();
return -1;
}
}
bfd_init();
kbuff = get_log_buff(file, &klen);
if (!kbuff) {
fprintf(stderr, "Could not retrieve log buffer!\n");
return -1;
}
image = get_last_jit_image(kbuff, klen, &len);
if (!image) {
fprintf(stderr, "No JIT image found!\n");
goto done;
}
if (!ofile) {
get_asm_insns(image, len, opcodes);
goto done;
}
ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
if (ofd < 0) {
fprintf(stderr, "Could not open file %s for writing: ", ofile);
perror(NULL);
goto done;
}
pos = image;
do {
nr = write(ofd, pos, len);
if (nr < 0) {
fprintf(stderr, "Could not write data to %s: ", ofile);
perror(NULL);
goto done;
}
len -= nr;
pos += nr;
} while (len);
close(ofd);
done:
put_log_buff(kbuff);
free(image);
return 0;
}
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