Root/samples/seccomp/bpf-helper.h

1/*
2 * Example wrapper around BPF macros.
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_SET_SECCOMP, 2, ...).
10 *
11 * No guarantees are provided with respect to the correctness
12 * or functionality of this code.
13 */
14#ifndef __BPF_HELPER_H__
15#define __BPF_HELPER_H__
16
17#include <asm/bitsperlong.h> /* for __BITS_PER_LONG */
18#include <endian.h>
19#include <linux/filter.h>
20#include <linux/seccomp.h> /* for seccomp_data */
21#include <linux/types.h>
22#include <linux/unistd.h>
23#include <stddef.h>
24
25#define BPF_LABELS_MAX 256
26struct bpf_labels {
27    int count;
28    struct __bpf_label {
29        const char *label;
30        __u32 location;
31    } labels[BPF_LABELS_MAX];
32};
33
34int bpf_resolve_jumps(struct bpf_labels *labels,
35              struct sock_filter *filter, size_t count);
36__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label);
37void seccomp_bpf_print(struct sock_filter *filter, size_t count);
38
39#define JUMP_JT 0xff
40#define JUMP_JF 0xff
41#define LABEL_JT 0xfe
42#define LABEL_JF 0xfe
43
44#define ALLOW \
45    BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
46#define DENY \
47    BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
48#define JUMP(labels, label) \
49    BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
50         JUMP_JT, JUMP_JF)
51#define LABEL(labels, label) \
52    BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
53         LABEL_JT, LABEL_JF)
54#define SYSCALL(nr, jt) \
55    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), \
56    jt
57
58/* Lame, but just an example */
59#define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label)
60
61#define EXPAND(...) __VA_ARGS__
62
63/* Ensure that we load the logically correct offset. */
64#if __BYTE_ORDER == __LITTLE_ENDIAN
65#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
66#elif __BYTE_ORDER == __BIG_ENDIAN
67#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
68#else
69#error "Unknown endianness"
70#endif
71
72/* Map all width-sensitive operations */
73#if __BITS_PER_LONG == 32
74
75#define JEQ(x, jt) JEQ32(x, EXPAND(jt))
76#define JNE(x, jt) JNE32(x, EXPAND(jt))
77#define JGT(x, jt) JGT32(x, EXPAND(jt))
78#define JLT(x, jt) JLT32(x, EXPAND(jt))
79#define JGE(x, jt) JGE32(x, EXPAND(jt))
80#define JLE(x, jt) JLE32(x, EXPAND(jt))
81#define JA(x, jt) JA32(x, EXPAND(jt))
82#define ARG(i) ARG_32(i)
83
84#elif __BITS_PER_LONG == 64
85
86/* Ensure that we load the logically correct offset. */
87#if __BYTE_ORDER == __LITTLE_ENDIAN
88#define ENDIAN(_lo, _hi) _lo, _hi
89#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
90#elif __BYTE_ORDER == __BIG_ENDIAN
91#define ENDIAN(_lo, _hi) _hi, _lo
92#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
93#endif
94
95union arg64 {
96    struct {
97        __u32 ENDIAN(lo32, hi32);
98    };
99    __u64 u64;
100};
101
102#define JEQ(x, jt) \
103    JEQ64(((union arg64){.u64 = (x)}).lo32, \
104          ((union arg64){.u64 = (x)}).hi32, \
105          EXPAND(jt))
106#define JGT(x, jt) \
107    JGT64(((union arg64){.u64 = (x)}).lo32, \
108          ((union arg64){.u64 = (x)}).hi32, \
109          EXPAND(jt))
110#define JGE(x, jt) \
111    JGE64(((union arg64){.u64 = (x)}).lo32, \
112          ((union arg64){.u64 = (x)}).hi32, \
113          EXPAND(jt))
114#define JNE(x, jt) \
115    JNE64(((union arg64){.u64 = (x)}).lo32, \
116          ((union arg64){.u64 = (x)}).hi32, \
117          EXPAND(jt))
118#define JLT(x, jt) \
119    JLT64(((union arg64){.u64 = (x)}).lo32, \
120          ((union arg64){.u64 = (x)}).hi32, \
121          EXPAND(jt))
122#define JLE(x, jt) \
123    JLE64(((union arg64){.u64 = (x)}).lo32, \
124          ((union arg64){.u64 = (x)}).hi32, \
125          EXPAND(jt))
126
127#define JA(x, jt) \
128    JA64(((union arg64){.u64 = (x)}).lo32, \
129           ((union arg64){.u64 = (x)}).hi32, \
130           EXPAND(jt))
131#define ARG(i) ARG_64(i)
132
133#else
134#error __BITS_PER_LONG value unusable.
135#endif
136
137/* Loads the arg into A */
138#define ARG_32(idx) \
139    BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx))
140
141/* Loads hi into A and lo in X */
142#define ARG_64(idx) \
143    BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \
144    BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
145    BPF_STMT(BPF_LD+BPF_W+BPF_ABS, HI_ARG(idx)), \
146    BPF_STMT(BPF_ST, 1) /* hi -> M[1] */
147
148#define JEQ32(value, jt) \
149    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 0, 1), \
150    jt
151
152#define JNE32(value, jt) \
153    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \
154    jt
155
156/* Checks the lo, then swaps to check the hi. A=lo,X=hi */
157#define JEQ64(lo, hi, jt) \
158    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
159    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
160    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \
161    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
162    jt, \
163    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
164
165#define JNE64(lo, hi, jt) \
166    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 5, 0), \
167    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
168    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \
169    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
170    jt, \
171    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
172
173#define JA32(value, jt) \
174    BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
175    jt
176
177#define JA64(lo, hi, jt) \
178    BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \
179    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
180    BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \
181    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
182    jt, \
183    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
184
185#define JGE32(value, jt) \
186    BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
187    jt
188
189#define JLT32(value, jt) \
190    BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
191    jt
192
193/* Shortcut checking if hi > arg.hi. */
194#define JGE64(lo, hi, jt) \
195    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
196    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
197    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
198    BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \
199    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
200    jt, \
201    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
202
203#define JLT64(lo, hi, jt) \
204    BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
205    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
206    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
207    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
208    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
209    jt, \
210    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
211
212#define JGT32(value, jt) \
213    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
214    jt
215
216#define JLE32(value, jt) \
217    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
218    jt
219
220/* Check hi > args.hi first, then do the GE checking */
221#define JGT64(lo, hi, jt) \
222    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
223    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
224    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
225    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \
226    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
227    jt, \
228    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
229
230#define JLE64(lo, hi, jt) \
231    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 6, 0), \
232    BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
233    BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
234    BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
235    BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
236    jt, \
237    BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
238
239#define LOAD_SYSCALL_NR \
240    BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
241         offsetof(struct seccomp_data, nr))
242
243#endif /* __BPF_HELPER_H__ */
244

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