1 /* bpf.h
2 * Copyright 2012 The ChromiumOS Authors
3 * Use of this source code is governed by a BSD-style license that can be
4 * found in the LICENSE file.
5 *
6 * Berkeley Packet Filter functions.
7 */
8
9 #ifndef BPF_H
10 #define BPF_H
11
12 #include <asm/bitsperlong.h> /* for __BITS_PER_LONG */
13 #include <endian.h>
14 #include <linux/audit.h>
15 #include <linux/filter.h>
16 #include <stddef.h>
17 #include <sys/user.h>
18
19 #ifdef __cplusplus
20 extern "C" {
21 #endif
22
23 #include "arch.h"
24
25 #if __BITS_PER_LONG == 32 || defined(__ILP32__)
26 #define BITS32
27 #elif __BITS_PER_LONG == 64
28 #define BITS64
29 #endif
30
31 /* Constants for comparison operators. */
32 #define MIN_OPERATOR 128
33 enum {
34 EQ = MIN_OPERATOR,
35 NE,
36 LT,
37 LE,
38 GT,
39 GE,
40 SET,
41 IN
42 };
43
44 /*
45 * BPF return values and data structures,
46 * since they're not yet in the kernel.
47 * TODO(crbug.com/1147037): Replace this with an #include.
48 */
49
50 #define SECCOMP_RET_KILL_PROCESS 0x80000000U /* kill the entire process */
51 #define SECCOMP_RET_KILL_THREAD 0x00000000U /* kill the thread */
52 #define SECCOMP_RET_KILL SECCOMP_RET_KILL_THREAD
53 #define SECCOMP_RET_TRAP 0x00030000U /* return SIGSYS */
54 #define SECCOMP_RET_ERRNO 0x00050000U /* return -1 and set errno */
55 #define SECCOMP_RET_LOG 0x7ffc0000U /* allow after logging */
56 #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
57
58 #define SECCOMP_RET_DATA 0x0000ffffU /* mask for return value */
59
60 struct seccomp_data {
61 int nr;
62 __u32 arch;
63 __u64 instruction_pointer;
64 __u64 args[6];
65 };
66
67 #define syscall_nr (offsetof(struct seccomp_data, nr))
68 #define arch_nr (offsetof(struct seccomp_data, arch))
69
70 /* Size-dependent defines. */
71 #if defined(BITS32)
72 /*
73 * On 32 bits, comparisons take 2 instructions: 1 for loading the argument,
74 * 1 for the actual comparison.
75 */
76 #define BPF_LOAD_ARG_LEN 1U
77 #define BPF_COMP_LEN 1U
78 #define BPF_SHORT_GT_GE_COMP_LEN 1U
79 #define BPF_GT_GE_COMP_LEN 1U
80 #define BPF_ARG_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_COMP_LEN)
81 #define BPF_ARG_SHORT_GT_GE_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_SHORT_GT_GE_COMP_LEN)
82 #define BPF_ARG_GT_GE_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_GT_GE_COMP_LEN)
83
84 #define bpf_comp_jeq bpf_comp_jeq32
85 #define bpf_comp_jgt bpf_comp_jgt32
86 #define bpf_comp_jge bpf_comp_jge32
87 #define bpf_comp_jset bpf_comp_jset32
88
89 #define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
90
91 #elif defined(BITS64)
92 /*
93 * On 64 bits, comparisons take 7-8 instructions: 4 for loading the argument,
94 * and 3-4 for the actual comparison.
95 */
96 #define BPF_LOAD_ARG_LEN 4U
97 #define BPF_COMP_LEN 3U
98 #define BPF_SHORT_GT_GE_COMP_LEN 3U
99 #define BPF_GT_GE_COMP_LEN 4U
100 #define BPF_ARG_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_COMP_LEN)
101 #define BPF_ARG_SHORT_GT_GE_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_SHORT_GT_GE_COMP_LEN)
102 #define BPF_ARG_GT_GE_COMP_LEN (BPF_LOAD_ARG_LEN + BPF_GT_GE_COMP_LEN)
103
104 #define bpf_comp_jeq bpf_comp_jeq64
105 #define bpf_comp_jgt bpf_comp_jgt64
106 #define bpf_comp_jge bpf_comp_jge64
107 #define bpf_comp_jset bpf_comp_jset64
108
109 /* Ensure that we load the logically correct offset. */
110 #if defined(__LITTLE_ENDIAN__) || __BYTE_ORDER == __LITTLE_ENDIAN
111 #define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
112 #define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
113 #else
114 #error "Unsupported endianness"
115 #endif
116
117 #else
118 #error "Unknown bit width"
119
120 #endif
121
122 /* Common jump targets. */
123 #define NEXT 0
124 #define SKIP 1
125 #define SKIPN(_n) (_n)
126
127 /* Support for labels in BPF programs. */
128 #define JUMP_JT 0xff
129 #define JUMP_JF 0xff
130 #define LABEL_JT 0xfe
131 #define LABEL_JF 0xfe
132
133 #define MAX_BPF_LABEL_LEN 32
134
135 #define BPF_LABELS_MAX 512U /* Each syscall could have an argument block. */
136 struct bpf_labels {
137 size_t count;
138 struct __bpf_label {
139 const char *label;
140 unsigned int location;
141 } labels[BPF_LABELS_MAX];
142 };
143
144 /* BPF instruction manipulation functions and macros. */
set_bpf_instr(struct sock_filter * instr,unsigned short code,unsigned int k,unsigned char jt,unsigned char jf)145 static inline size_t set_bpf_instr(struct sock_filter *instr,
146 unsigned short code, unsigned int k,
147 unsigned char jt, unsigned char jf)
148 {
149 instr->code = code;
150 instr->k = k;
151 instr->jt = jt;
152 instr->jf = jf;
153 return 1U;
154 }
155
156 #define set_bpf_stmt(_block, _code, _k) \
157 set_bpf_instr((_block), (_code), (_k), 0, 0)
158
159 #define set_bpf_jump(_block, _code, _k, _jt, _jf) \
160 set_bpf_instr((_block), (_code), (_k), (_jt), (_jf))
161
162 #define set_bpf_lbl(_block, _lbl_id) \
163 set_bpf_jump((_block), BPF_JMP+BPF_JA, (_lbl_id), \
164 LABEL_JT, LABEL_JF)
165
166 #define set_bpf_jump_lbl(_block, _lbl_id) \
167 set_bpf_jump((_block), BPF_JMP+BPF_JA, (_lbl_id), \
168 JUMP_JT, JUMP_JF)
169
170 #define set_bpf_ret_kill(_block) \
171 set_bpf_stmt((_block), BPF_RET+BPF_K, SECCOMP_RET_KILL)
172
173 #define set_bpf_ret_kill_process(_block) \
174 set_bpf_stmt((_block), BPF_RET+BPF_K, SECCOMP_RET_KILL_PROCESS)
175
176 #define set_bpf_ret_trap(_block) \
177 set_bpf_stmt((_block), BPF_RET+BPF_K, SECCOMP_RET_TRAP)
178
179 #define set_bpf_ret_errno(_block, _errno) \
180 set_bpf_stmt((_block), BPF_RET+BPF_K, \
181 SECCOMP_RET_ERRNO | ((_errno) & SECCOMP_RET_DATA))
182
183 #define set_bpf_ret_log(_block) \
184 set_bpf_stmt((_block), BPF_RET+BPF_K, SECCOMP_RET_LOG)
185
186 #define set_bpf_ret_allow(_block) \
187 set_bpf_stmt((_block), BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
188
189 #define bpf_load_syscall_nr(_filter) \
190 set_bpf_stmt((_filter), BPF_LD+BPF_W+BPF_ABS, syscall_nr)
191
192 /* BPF label functions. */
193 int bpf_resolve_jumps(struct bpf_labels *labels,
194 struct sock_filter *filter, size_t count);
195 int bpf_label_id(struct bpf_labels *labels, const char *label);
196 void free_label_strings(struct bpf_labels *labels);
197
198 /* BPF helper functions. */
199 size_t bpf_load_arg(struct sock_filter *filter, int argidx);
200 size_t bpf_comp_jeq(struct sock_filter *filter, unsigned long c,
201 unsigned char jt, unsigned char jf);
202 size_t bpf_comp_jgt(struct sock_filter *filter, unsigned long c,
203 unsigned char jt, unsigned char jf);
204 size_t bpf_comp_jge(struct sock_filter *filter, unsigned long c,
205 unsigned char jt, unsigned char jf);
206 size_t bpf_comp_jset(struct sock_filter *filter, unsigned long mask,
207 unsigned char jt, unsigned char jf);
208 size_t bpf_comp_jin(struct sock_filter *filter, unsigned long mask,
209 unsigned char jt, unsigned char jf);
210
211 /* Functions called by syscall_filter.c */
212 #define ARCH_VALIDATION_LEN 3U
213 #define ALLOW_SYSCALL_LEN 2U
214
215 size_t bpf_arg_comp(struct sock_filter **pfilter,
216 int op, int argidx, unsigned long c, unsigned int label_id);
217 size_t bpf_validate_arch(struct sock_filter *filter);
218 size_t bpf_allow_syscall(struct sock_filter *filter, int nr);
219 size_t bpf_allow_syscall_args(struct sock_filter *filter,
220 int nr, unsigned int id);
221
222 #ifdef __cplusplus
223 }; /* extern "C" */
224 #endif
225
226 #endif /* BPF_H */
227