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Linux/samples/seccomp/bpf-helper.c

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  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 
 18 int bpf_resolve_jumps(struct bpf_labels *labels,
 19                       struct sock_filter *filter, size_t count)
 20 {
 21         struct sock_filter *begin = filter;
 22         __u8 insn = count - 1;
 23 
 24         if (count < 1)
 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         filter += insn;
 31         for (; filter >= begin; --insn, --filter) {
 32                 if (filter->code != (BPF_JMP+BPF_JA))
 33                         continue;
 34                 switch ((filter->jt<<8)|filter->jf) {
 35                 case (JUMP_JT<<8)|JUMP_JF:
 36                         if (labels->labels[filter->k].location == 0xffffffff) {
 37                                 fprintf(stderr, "Unresolved label: '%s'\n",
 38                                         labels->labels[filter->k].label);
 39                                 return 1;
 40                         }
 41                         filter->k = labels->labels[filter->k].location -
 42                                     (insn + 1);
 43                         filter->jt = 0;
 44                         filter->jf = 0;
 45                         continue;
 46                 case (LABEL_JT<<8)|LABEL_JF:
 47                         if (labels->labels[filter->k].location != 0xffffffff) {
 48                                 fprintf(stderr, "Duplicate label use: '%s'\n",
 49                                         labels->labels[filter->k].label);
 50                                 return 1;
 51                         }
 52                         labels->labels[filter->k].location = insn;
 53                         filter->k = 0; /* fall through */
 54                         filter->jt = 0;
 55                         filter->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 
 89 void 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 

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