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

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Seccomp BPF helper functions
   4 *
   5 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   6 * Author: Will Drewry <wad@chromium.org>
   7 *
   8 * The code may be used by anyone for any purpose,
   9 * and can serve as a starting point for developing
  10 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
  11 */
  12
  13#include <stdio.h>
  14#include <stdlib.h>
  15#include <string.h>
  16
  17#include "bpf-helper.h"
  18
  19int bpf_resolve_jumps(struct bpf_labels *labels,
  20                      struct sock_filter *filter, size_t count)
  21{
  22        size_t i;
  23
  24        if (count < 1 || count > BPF_MAXINSNS)
  25                return -1;
  26        /*
  27        * Walk it once, backwards, to build the label table and do fixups.
  28        * Since backward jumps are disallowed by BPF, this is easy.
  29        */
  30        for (i = 0; i < count; ++i) {
  31                size_t offset = count - i - 1;
  32                struct sock_filter *instr = &filter[offset];
  33                if (instr->code != (BPF_JMP+BPF_JA))
  34                        continue;
  35                switch ((instr->jt<<8)|instr->jf) {
  36                case (JUMP_JT<<8)|JUMP_JF:
  37                        if (labels->labels[instr->k].location == 0xffffffff) {
  38                                fprintf(stderr, "Unresolved label: '%s'\n",
  39                                        labels->labels[instr->k].label);
  40                                return 1;
  41                        }
  42                        instr->k = labels->labels[instr->k].location -
  43                                    (offset + 1);
  44                        instr->jt = 0;
  45                        instr->jf = 0;
  46                        continue;
  47                case (LABEL_JT<<8)|LABEL_JF:
  48                        if (labels->labels[instr->k].location != 0xffffffff) {
  49                                fprintf(stderr, "Duplicate label use: '%s'\n",
  50                                        labels->labels[instr->k].label);
  51                                return 1;
  52                        }
  53                        labels->labels[instr->k].location = offset;
  54                        instr->k = 0; /* fall through */
  55                        instr->jt = 0;
  56                        instr->jf = 0;
  57                        continue;
  58                }
  59        }
  60        return 0;
  61}
  62
  63/* Simple lookup table for labels. */
  64__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
  65{
  66        struct __bpf_label *begin = labels->labels, *end;
  67        int id;
  68
  69        if (labels->count == BPF_LABELS_MAX) {
  70                fprintf(stderr, "Too many labels\n");
  71                exit(1);
  72        }
  73        if (labels->count == 0) {
  74                begin->label = label;
  75                begin->location = 0xffffffff;
  76                labels->count++;
  77                return 0;
  78        }
  79        end = begin + labels->count;
  80        for (id = 0; begin < end; ++begin, ++id) {
  81                if (!strcmp(label, begin->label))
  82                        return id;
  83        }
  84        begin->label = label;
  85        begin->location = 0xffffffff;
  86        labels->count++;
  87        return id;
  88}
  89
  90void seccomp_bpf_print(struct sock_filter *filter, size_t count)
  91{
  92        struct sock_filter *end = filter + count;
  93        for ( ; filter < end; ++filter)
  94                printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
  95                        filter->code, filter->jt, filter->jf, filter->k);
  96}
  97