1 /*
2 * Decoder of classic BPF programs.
3 *
4 * Copyright (c) 2015-2017 Dmitry V. Levin <ldv@altlinux.org>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. The name of the author may not be used to endorse or promote products
16 * derived from this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29
30 #include "defs.h"
31
32 #include "bpf_filter.h"
33 #include "bpf_fprog.h"
34
35 #include <linux/filter.h>
36 #include "xlat/bpf_class.h"
37 #include "xlat/bpf_miscop.h"
38 #include "xlat/bpf_mode.h"
39 #include "xlat/bpf_op_alu.h"
40 #include "xlat/bpf_op_jmp.h"
41 #include "xlat/bpf_rval.h"
42 #include "xlat/bpf_size.h"
43 #include "xlat/bpf_src.h"
44
45 static void
print_bpf_filter_code(const uint16_t code)46 print_bpf_filter_code(const uint16_t code)
47 {
48 uint16_t i = code & ~BPF_CLASS(code);
49
50 printxval(bpf_class, BPF_CLASS(code), "BPF_???");
51 switch (BPF_CLASS(code)) {
52 case BPF_LD:
53 case BPF_LDX:
54 tprints("|");
55 printxval(bpf_size, BPF_SIZE(code), "BPF_???");
56 tprints("|");
57 printxval(bpf_mode, BPF_MODE(code), "BPF_???");
58 break;
59 case BPF_ST:
60 case BPF_STX:
61 if (i) {
62 tprintf("|%#x", i);
63 tprints_comment("BPF_???");
64 }
65 break;
66 case BPF_ALU:
67 tprints("|");
68 printxval(bpf_src, BPF_SRC(code), "BPF_???");
69 tprints("|");
70 printxval(bpf_op_alu, BPF_OP(code), "BPF_???");
71 break;
72 case BPF_JMP:
73 tprints("|");
74 printxval(bpf_src, BPF_SRC(code), "BPF_???");
75 tprints("|");
76 printxval(bpf_op_jmp, BPF_OP(code), "BPF_???");
77 break;
78 case BPF_RET:
79 tprints("|");
80 printxval(bpf_rval, BPF_RVAL(code), "BPF_???");
81 i &= ~BPF_RVAL(code);
82 if (i) {
83 tprintf("|%#x", i);
84 tprints_comment("BPF_???");
85 }
86 break;
87 case BPF_MISC:
88 tprints("|");
89 printxval(bpf_miscop, BPF_MISCOP(code), "BPF_???");
90 i &= ~BPF_MISCOP(code);
91 if (i) {
92 tprintf("|%#x", i);
93 tprints_comment("BPF_???");
94 }
95 break;
96 }
97 }
98
99 static void
print_bpf_filter_stmt(const struct bpf_filter_block * const filter,const print_bpf_filter_fn print_k)100 print_bpf_filter_stmt(const struct bpf_filter_block *const filter,
101 const print_bpf_filter_fn print_k)
102 {
103 tprints("BPF_STMT(");
104 print_bpf_filter_code(filter->code);
105 tprints(", ");
106 if (!print_k || !print_k(filter))
107 tprintf("%#x", filter->k);
108 tprints(")");
109 }
110
111 static void
print_bpf_filter_jump(const struct bpf_filter_block * const filter)112 print_bpf_filter_jump(const struct bpf_filter_block *const filter)
113 {
114 tprints("BPF_JUMP(");
115 print_bpf_filter_code(filter->code);
116 tprintf(", %#x, %#x, %#x)", filter->k, filter->jt, filter->jf);
117 }
118
119 struct bpf_filter_block_data {
120 const print_bpf_filter_fn fn;
121 unsigned int count;
122 };
123
124 static bool
print_bpf_filter_block(struct tcb * const tcp,void * const elem_buf,const size_t elem_size,void * const data)125 print_bpf_filter_block(struct tcb *const tcp, void *const elem_buf,
126 const size_t elem_size, void *const data)
127 {
128 const struct bpf_filter_block *const filter = elem_buf;
129 struct bpf_filter_block_data *const fbd = data;
130
131 if (fbd->count++ >= BPF_MAXINSNS) {
132 tprints("...");
133 return false;
134 }
135
136 if (filter->jt || filter->jf)
137 print_bpf_filter_jump(filter);
138 else
139 print_bpf_filter_stmt(filter, fbd->fn);
140
141 return true;
142 }
143
144 void
print_bpf_fprog(struct tcb * const tcp,const kernel_ulong_t addr,const unsigned short len,const print_bpf_filter_fn print_k)145 print_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
146 const unsigned short len, const print_bpf_filter_fn print_k)
147 {
148 if (abbrev(tcp)) {
149 printaddr(addr);
150 } else {
151 struct bpf_filter_block_data fbd = { .fn = print_k };
152 struct bpf_filter_block filter;
153
154 print_array(tcp, addr, len, &filter, sizeof(filter),
155 umoven_or_printaddr, print_bpf_filter_block, &fbd);
156 }
157 }
158
159 void
decode_bpf_fprog(struct tcb * const tcp,const kernel_ulong_t addr,const print_bpf_filter_fn print_k)160 decode_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
161 const print_bpf_filter_fn print_k)
162 {
163 struct bpf_fprog fprog;
164
165 if (fetch_bpf_fprog(tcp, addr, &fprog)) {
166 tprintf("{len=%hu, filter=", fprog.len);
167 print_bpf_fprog(tcp, fprog.filter, fprog.len, print_k);
168 tprints("}");
169 }
170 }
171