Merge tag 'docs-5.2' of git://git.lwn.net/linux
[sfrench/cifs-2.6.git] / samples / seccomp / bpf-helper.c
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
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. */
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
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 }