1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
|
// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package bpf
import (
"bytes"
"fmt"
"gvisor.dev/gvisor/pkg/abi/linux"
)
// DecodeProgram translates a compiled BPF program into text format.
func DecodeProgram(p Program) (string, error) {
return DecodeInstructions(p.instructions)
}
// DecodeInstructions translates an array of BPF instructions into text format.
func DecodeInstructions(instns []linux.BPFInstruction) (string, error) {
var ret bytes.Buffer
for line, s := range instns {
ret.WriteString(fmt.Sprintf("%v: ", line))
if err := decode(s, line, &ret); err != nil {
return "", err
}
ret.WriteString("\n")
}
return ret.String(), nil
}
// Decode translates a single BPF instruction into text format.
func Decode(inst linux.BPFInstruction) (string, error) {
var ret bytes.Buffer
err := decode(inst, -1, &ret)
return ret.String(), err
}
func decode(inst linux.BPFInstruction, line int, w *bytes.Buffer) error {
var err error
switch inst.OpCode & instructionClassMask {
case Ld:
err = decodeLd(inst, w)
case Ldx:
err = decodeLdx(inst, w)
case St:
w.WriteString(fmt.Sprintf("M[%v] <- A", inst.K))
case Stx:
w.WriteString(fmt.Sprintf("M[%v] <- X", inst.K))
case Alu:
err = decodeAlu(inst, w)
case Jmp:
err = decodeJmp(inst, line, w)
case Ret:
err = decodeRet(inst, w)
case Misc:
err = decodeMisc(inst, w)
default:
return fmt.Errorf("invalid BPF instruction: %v", inst)
}
return err
}
// A <- P[k:4]
func decodeLd(inst linux.BPFInstruction, w *bytes.Buffer) error {
w.WriteString("A <- ")
switch inst.OpCode & loadModeMask {
case Imm:
w.WriteString(fmt.Sprintf("%v", inst.K))
case Abs:
w.WriteString(fmt.Sprintf("P[%v:", inst.K))
if err := decodeLdSize(inst, w); err != nil {
return err
}
w.WriteString("]")
case Ind:
w.WriteString(fmt.Sprintf("P[X+%v:", inst.K))
if err := decodeLdSize(inst, w); err != nil {
return err
}
w.WriteString("]")
case Mem:
w.WriteString(fmt.Sprintf("M[%v]", inst.K))
case Len:
w.WriteString("len")
default:
return fmt.Errorf("invalid BPF LD instruction: %v", inst)
}
return nil
}
func decodeLdSize(inst linux.BPFInstruction, w *bytes.Buffer) error {
switch inst.OpCode & loadSizeMask {
case W:
w.WriteString("4")
case H:
w.WriteString("2")
case B:
w.WriteString("1")
default:
return fmt.Errorf("Invalid BPF LD size: %v", inst)
}
return nil
}
// X <- P[k:4]
func decodeLdx(inst linux.BPFInstruction, w *bytes.Buffer) error {
w.WriteString("X <- ")
switch inst.OpCode & loadModeMask {
case Imm:
w.WriteString(fmt.Sprintf("%v", inst.K))
case Mem:
w.WriteString(fmt.Sprintf("M[%v]", inst.K))
case Len:
w.WriteString("len")
case Msh:
w.WriteString(fmt.Sprintf("4*(P[%v:1]&0xf)", inst.K))
default:
return fmt.Errorf("invalid BPF LDX instruction: %v", inst)
}
return nil
}
// A <- A + k
func decodeAlu(inst linux.BPFInstruction, w *bytes.Buffer) error {
code := inst.OpCode & aluMask
if code == Neg {
w.WriteString("A <- -A")
return nil
}
w.WriteString("A <- A ")
switch code {
case Add:
w.WriteString("+ ")
case Sub:
w.WriteString("- ")
case Mul:
w.WriteString("* ")
case Div:
w.WriteString("/ ")
case Or:
w.WriteString("| ")
case And:
w.WriteString("& ")
case Lsh:
w.WriteString("<< ")
case Rsh:
w.WriteString(">> ")
case Mod:
w.WriteString("% ")
case Xor:
w.WriteString("^ ")
default:
return fmt.Errorf("invalid BPF ALU instruction: %v", inst)
}
return decodeSource(inst, w)
}
func decodeSource(inst linux.BPFInstruction, w *bytes.Buffer) error {
switch inst.OpCode & srcAluJmpMask {
case K:
w.WriteString(fmt.Sprintf("%v", inst.K))
case X:
w.WriteString("X")
default:
return fmt.Errorf("invalid BPF ALU/JMP source instruction: %v", inst)
}
return nil
}
// pc += (A > k) ? jt : jf
func decodeJmp(inst linux.BPFInstruction, line int, w *bytes.Buffer) error {
code := inst.OpCode & jmpMask
w.WriteString("pc += ")
if code == Ja {
w.WriteString(printJmpTarget(inst.K, line))
} else {
w.WriteString("(A ")
switch code {
case Jeq:
w.WriteString("== ")
case Jgt:
w.WriteString("> ")
case Jge:
w.WriteString(">= ")
case Jset:
w.WriteString("& ")
default:
return fmt.Errorf("invalid BPF ALU instruction: %v", inst)
}
if err := decodeSource(inst, w); err != nil {
return err
}
w.WriteString(
fmt.Sprintf(") ? %s : %s",
printJmpTarget(uint32(inst.JumpIfTrue), line),
printJmpTarget(uint32(inst.JumpIfFalse), line)))
}
return nil
}
func printJmpTarget(target uint32, line int) string {
if line == -1 {
return fmt.Sprintf("%v", target)
}
return fmt.Sprintf("%v [%v]", target, int(target)+line+1)
}
// ret k
func decodeRet(inst linux.BPFInstruction, w *bytes.Buffer) error {
w.WriteString("ret ")
code := inst.OpCode & srcRetMask
switch code {
case K:
w.WriteString(fmt.Sprintf("%v", inst.K))
case A:
w.WriteString("A")
default:
return fmt.Errorf("invalid BPF RET source instruction: %v", inst)
}
return nil
}
func decodeMisc(inst linux.BPFInstruction, w *bytes.Buffer) error {
code := inst.OpCode & miscMask
switch code {
case Tax:
w.WriteString("X <- A")
case Txa:
w.WriteString("A <- X")
default:
return fmt.Errorf("invalid BPF ALU/JMP source instruction: %v", inst)
}
return nil
}
|
