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
bpf_resolve_jumps(struct bpf_labels * labels,struct sock_filter * filter,size_t count)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. */
seccomp_bpf_label(struct bpf_labels * labels,const char * label)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
seccomp_bpf_print(struct sock_filter * filter,size_t count)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 }
97