LXR linux/samples/seccomp/bpf-helper.c

   1/*
   2 * Seccomp BPF helper functions
   3 *
   4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   5 * Author: Will Drewry <wad@chromium.org>
   6 *
   7 * The code may be used by anyone for any purpose,
   8 * and can serve as a starting point for developing
   9 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
  10 */
  11
  12#include <stdio.h>
  13#include <stdlib.h>
  14#include <string.h>
  15
  16#include "bpf-helper.h"
  17
  18int bpf_resolve_jumps(struct bpf_labels *labels,
  19                      struct sock_filter *filter, size_t count)
  20{
  21        size_t i;
  22
  23        if (count < 1 || count > BPF_MAXINSNS)
  24                return -1;
  25        /*
  26        * Walk it once, backwards, to build the label table and do fixups.
  27        * Since backward jumps are disallowed by BPF, this is easy.
  28        */
  29        for (i = 0; i < count; ++i) {
  30                size_t offset = count - i - 1;
  31                struct sock_filter *instr = &filter[offset];
  32                if (instr->code != (BPF_JMP+BPF_JA))
  33                        continue;
  34                switch ((instr->jt<<8)|instr->jf) {
  35                case (JUMP_JT<<8)|JUMP_JF:
  36                        if (labels->labels[instr->k].location == 0xffffffff) {
  37                                fprintf(stderr, "Unresolved label: '%s'\n",
  38                                        labels->labels[instr->k].label);
  39                                return 1;
  40                        }
  41                        instr->k = labels->labels[instr->k].location -
  42                                    (offset + 1);
  43                        instr->jt = 0;
  44                        instr->jf = 0;
  45                        continue;
  46                case (LABEL_JT<<8)|LABEL_JF:
  47                        if (labels->labels[instr->k].location != 0xffffffff) {
  48                                fprintf(stderr, "Duplicate label use: '%s'\n",
  49                                        labels->labels[instr->k].label);
  50                                return 1;
  51                        }
  52                        labels->labels[instr->k].location = offset;
  53                        instr->k = 0; /* fall through */
  54                        instr->jt = 0;
  55                        instr->jf = 0;
  56                        continue;
  57                }
  58        }
  59        return 0;
  60}
  61
  62/* Simple lookup table for labels. */
  63__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
  64{
  65        struct __bpf_label *begin = labels->labels, *end;
  66        int id;
  67
  68        if (labels->count == BPF_LABELS_MAX) {
  69                fprintf(stderr, "Too many labels\n");
  70                exit(1);
  71        }
  72        if (labels->count == 0) {
  73                begin->label = label;
  74                begin->location = 0xffffffff;
  75                labels->count++;
  76                return 0;
  77        }
  78        end = begin + labels->count;
  79        for (id = 0; begin < end; ++begin, ++id) {
  80                if (!strcmp(label, begin->label))
  81                        return id;
  82        }
  83        begin->label = label;
  84        begin->location = 0xffffffff;
  85        labels->count++;
  86        return id;
  87}
  88
  89void seccomp_bpf_print(struct sock_filter *filter, size_t count)
  90{
  91        struct sock_filter *end = filter + count;
  92        for ( ; filter < end; ++filter)
  93                printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
  94                        filter->code, filter->jt, filter->jf, filter->k);
  95}
  96