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 <string.h>
14
15#include "bpf-helper.h"
16
17int bpf_resolve_jumps(struct bpf_labels *labels,
18		      struct sock_filter *filter, size_t count)
19{
20	struct sock_filter *begin = filter;
21	__u8 insn = count - 1;
22
23	if (count < 1)
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	filter += insn;
30	for (; filter >= begin; --insn, --filter) {
31		if (filter->code != (BPF_JMP+BPF_JA))
32			continue;
33		switch ((filter->jt<<8)|filter->jf) {
34		case (JUMP_JT<<8)|JUMP_JF:
35			if (labels->labels[filter->k].location == 0xffffffff) {
36				fprintf(stderr, "Unresolved label: '%s'\n",
37					labels->labels[filter->k].label);
38				return 1;
39			}
40			filter->k = labels->labels[filter->k].location -
41				    (insn + 1);
42			filter->jt = 0;
43			filter->jf = 0;
44			continue;
45		case (LABEL_JT<<8)|LABEL_JF:
46			if (labels->labels[filter->k].location != 0xffffffff) {
47				fprintf(stderr, "Duplicate label use: '%s'\n",
48					labels->labels[filter->k].label);
49				return 1;
50			}
51			labels->labels[filter->k].location = insn;
52			filter->k = 0; /* fall through */
53			filter->jt = 0;
54			filter->jf = 0;
55			continue;
56		}
57	}
58	return 0;
59}
60
61/* Simple lookup table for labels. */
62__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
63{
64	struct __bpf_label *begin = labels->labels, *end;
65	int id;
66	if (labels->count == 0) {
67		begin->label = label;
68		begin->location = 0xffffffff;
69		labels->count++;
70		return 0;
71	}
72	end = begin + labels->count;
73	for (id = 0; begin < end; ++begin, ++id) {
74		if (!strcmp(label, begin->label))
75			return id;
76	}
77	begin->label = label;
78	begin->location = 0xffffffff;
79	labels->count++;
80	return id;
81}
82
83void seccomp_bpf_print(struct sock_filter *filter, size_t count)
84{
85	struct sock_filter *end = filter + count;
86	for ( ; filter < end; ++filter)
87		printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
88			filter->code, filter->jt, filter->jf, filter->k);
89}