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8ac270d1 WD |
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 | ||
17 | int 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 | ||
83 | void 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 | } |