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![Alexei Starovoitov](/assets/img/avatar_default.png)
JITed seccomp filters can be quite large if they check a lot of syscalls Simply increase buffer size Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Acked-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
197 lines
4 KiB
C
197 lines
4 KiB
C
/*
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* Minimal BPF JIT image disassembler
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*
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* Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
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* debugging or verification purposes.
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*
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* To get the disassembly of the JIT code, do the following:
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*
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* 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
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* 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
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* 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
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*
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* Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
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* Licensed under the GNU General Public License, version 2.0 (GPLv2)
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*/
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <assert.h>
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#include <unistd.h>
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#include <string.h>
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#include <bfd.h>
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#include <dis-asm.h>
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#include <sys/klog.h>
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#include <sys/types.h>
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#include <regex.h>
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static void get_exec_path(char *tpath, size_t size)
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{
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char *path;
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ssize_t len;
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snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
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tpath[size - 1] = 0;
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path = strdup(tpath);
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assert(path);
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len = readlink(path, tpath, size);
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tpath[len] = 0;
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free(path);
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}
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static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
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{
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int count, i, pc = 0;
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char tpath[256];
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struct disassemble_info info;
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disassembler_ftype disassemble;
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bfd *bfdf;
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memset(tpath, 0, sizeof(tpath));
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get_exec_path(tpath, sizeof(tpath));
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bfdf = bfd_openr(tpath, NULL);
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assert(bfdf);
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assert(bfd_check_format(bfdf, bfd_object));
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init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
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info.arch = bfd_get_arch(bfdf);
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info.mach = bfd_get_mach(bfdf);
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info.buffer = image;
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info.buffer_length = len;
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disassemble_init_for_target(&info);
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disassemble = disassembler(bfdf);
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assert(disassemble);
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do {
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printf("%4x:\t", pc);
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count = disassemble(pc, &info);
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if (opcodes) {
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printf("\n\t");
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for (i = 0; i < count; ++i)
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printf("%02x ", (uint8_t) image[pc + i]);
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}
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printf("\n");
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pc += count;
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} while(count > 0 && pc < len);
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bfd_close(bfdf);
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}
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static char *get_klog_buff(int *klen)
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{
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int ret, len = klogctl(10, NULL, 0);
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char *buff = malloc(len);
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assert(buff && klen);
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ret = klogctl(3, buff, len);
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assert(ret >= 0);
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*klen = ret;
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return buff;
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}
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static void put_klog_buff(char *buff)
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{
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free(buff);
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}
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static int get_last_jit_image(char *haystack, size_t hlen,
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uint8_t *image, size_t ilen)
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{
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char *ptr, *pptr, *tmp;
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off_t off = 0;
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int ret, flen, proglen, pass, ulen = 0;
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regmatch_t pmatch[1];
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unsigned long base;
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regex_t regex;
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if (hlen == 0)
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return 0;
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ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
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"pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
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assert(ret == 0);
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ptr = haystack;
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while (1) {
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ret = regexec(®ex, ptr, 1, pmatch, 0);
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if (ret == 0) {
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ptr += pmatch[0].rm_eo;
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off += pmatch[0].rm_eo;
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assert(off < hlen);
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} else
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break;
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}
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ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
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ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
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&flen, &proglen, &pass, &base);
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if (ret != 4)
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return 0;
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tmp = ptr = haystack + off;
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while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
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tmp = NULL;
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if (!strstr(ptr, "JIT code"))
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continue;
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pptr = ptr;
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while ((ptr = strstr(pptr, ":")))
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pptr = ptr + 1;
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ptr = pptr;
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do {
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image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
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if (ptr == pptr || ulen >= ilen) {
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ulen--;
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break;
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}
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ptr = pptr;
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} while (1);
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}
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assert(ulen == proglen);
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printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
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proglen, pass, flen);
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printf("%lx + <x>:\n", base);
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regfree(®ex);
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return ulen;
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}
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int main(int argc, char **argv)
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{
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int len, klen, opcodes = 0;
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char *kbuff;
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static uint8_t image[32768];
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if (argc > 1) {
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if (!strncmp("-o", argv[argc - 1], 2)) {
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opcodes = 1;
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} else {
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printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
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exit(0);
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}
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}
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bfd_init();
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memset(image, 0, sizeof(image));
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kbuff = get_klog_buff(&klen);
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len = get_last_jit_image(kbuff, klen, image, sizeof(image));
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if (len > 0)
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get_asm_insns(image, len, opcodes);
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put_klog_buff(kbuff);
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return 0;
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}
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