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  
bpf_resolve_jumps(struct bpf_labels * labels,struct sock_filter * filter,size_t count)19  int 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. */
seccomp_bpf_label(struct bpf_labels * labels,const char * label)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  
seccomp_bpf_print(struct sock_filter * filter,size_t count)90  void 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