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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 <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 | } |
90 |
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v2.6.34-rc5
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