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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
8ac270d1 WD |
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> | |
3a9af0bd | 14 | #include <stdlib.h> |
8ac270d1 WD |
15 | #include <string.h> |
16 | ||
17 | #include "bpf-helper.h" | |
18 | ||
19 | int bpf_resolve_jumps(struct bpf_labels *labels, | |
20 | struct sock_filter *filter, size_t count) | |
21 | { | |
d881d25c | 22 | size_t i; |
8ac270d1 | 23 | |
d881d25c | 24 | if (count < 1 || count > BPF_MAXINSNS) |
8ac270d1 WD |
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 | */ | |
d881d25c RZ |
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)) | |
8ac270d1 | 34 | continue; |
d881d25c | 35 | switch ((instr->jt<<8)|instr->jf) { |
8ac270d1 | 36 | case (JUMP_JT<<8)|JUMP_JF: |
d881d25c | 37 | if (labels->labels[instr->k].location == 0xffffffff) { |
8ac270d1 | 38 | fprintf(stderr, "Unresolved label: '%s'\n", |
d881d25c | 39 | labels->labels[instr->k].label); |
8ac270d1 WD |
40 | return 1; |
41 | } | |
d881d25c RZ |
42 | instr->k = labels->labels[instr->k].location - |
43 | (offset + 1); | |
44 | instr->jt = 0; | |
45 | instr->jf = 0; | |
8ac270d1 WD |
46 | continue; |
47 | case (LABEL_JT<<8)|LABEL_JF: | |
d881d25c | 48 | if (labels->labels[instr->k].location != 0xffffffff) { |
8ac270d1 | 49 | fprintf(stderr, "Duplicate label use: '%s'\n", |
d881d25c | 50 | labels->labels[instr->k].label); |
8ac270d1 WD |
51 | return 1; |
52 | } | |
d881d25c RZ |
53 | labels->labels[instr->k].location = offset; |
54 | instr->k = 0; /* fall through */ | |
55 | instr->jt = 0; | |
56 | instr->jf = 0; | |
8ac270d1 WD |
57 | continue; |
58 | } | |
59 | } | |
60 | return 0; | |
61 | } | |
62 | ||
63 | /* Simple lookup table for labels. */ | |
64 | __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label) | |
65 | { | |
66 | struct __bpf_label *begin = labels->labels, *end; | |
67 | int id; | |
3a9af0bd KC |
68 | |
69 | if (labels->count == BPF_LABELS_MAX) { | |
70 | fprintf(stderr, "Too many labels\n"); | |
71 | exit(1); | |
72 | } | |
8ac270d1 WD |
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 | ||
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 | } |