David K. Bainbridge | 215e024 | 2017-09-05 23:18:24 -0700 | [diff] [blame] | 1 | // Copyright 2016 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package bpf |
| 6 | |
| 7 | import ( |
| 8 | "encoding/binary" |
| 9 | "fmt" |
| 10 | ) |
| 11 | |
| 12 | func aluOpConstant(ins ALUOpConstant, regA uint32) uint32 { |
| 13 | return aluOpCommon(ins.Op, regA, ins.Val) |
| 14 | } |
| 15 | |
| 16 | func aluOpX(ins ALUOpX, regA uint32, regX uint32) (uint32, bool) { |
| 17 | // Guard against division or modulus by zero by terminating |
| 18 | // the program, as the OS BPF VM does |
| 19 | if regX == 0 { |
| 20 | switch ins.Op { |
| 21 | case ALUOpDiv, ALUOpMod: |
| 22 | return 0, false |
| 23 | } |
| 24 | } |
| 25 | |
| 26 | return aluOpCommon(ins.Op, regA, regX), true |
| 27 | } |
| 28 | |
| 29 | func aluOpCommon(op ALUOp, regA uint32, value uint32) uint32 { |
| 30 | switch op { |
| 31 | case ALUOpAdd: |
| 32 | return regA + value |
| 33 | case ALUOpSub: |
| 34 | return regA - value |
| 35 | case ALUOpMul: |
| 36 | return regA * value |
| 37 | case ALUOpDiv: |
| 38 | // Division by zero not permitted by NewVM and aluOpX checks |
| 39 | return regA / value |
| 40 | case ALUOpOr: |
| 41 | return regA | value |
| 42 | case ALUOpAnd: |
| 43 | return regA & value |
| 44 | case ALUOpShiftLeft: |
| 45 | return regA << value |
| 46 | case ALUOpShiftRight: |
| 47 | return regA >> value |
| 48 | case ALUOpMod: |
| 49 | // Modulus by zero not permitted by NewVM and aluOpX checks |
| 50 | return regA % value |
| 51 | case ALUOpXor: |
| 52 | return regA ^ value |
| 53 | default: |
| 54 | return regA |
| 55 | } |
| 56 | } |
| 57 | |
| 58 | func jumpIf(ins JumpIf, value uint32) int { |
| 59 | var ok bool |
| 60 | inV := uint32(ins.Val) |
| 61 | |
| 62 | switch ins.Cond { |
| 63 | case JumpEqual: |
| 64 | ok = value == inV |
| 65 | case JumpNotEqual: |
| 66 | ok = value != inV |
| 67 | case JumpGreaterThan: |
| 68 | ok = value > inV |
| 69 | case JumpLessThan: |
| 70 | ok = value < inV |
| 71 | case JumpGreaterOrEqual: |
| 72 | ok = value >= inV |
| 73 | case JumpLessOrEqual: |
| 74 | ok = value <= inV |
| 75 | case JumpBitsSet: |
| 76 | ok = (value & inV) != 0 |
| 77 | case JumpBitsNotSet: |
| 78 | ok = (value & inV) == 0 |
| 79 | } |
| 80 | |
| 81 | if ok { |
| 82 | return int(ins.SkipTrue) |
| 83 | } |
| 84 | |
| 85 | return int(ins.SkipFalse) |
| 86 | } |
| 87 | |
| 88 | func loadAbsolute(ins LoadAbsolute, in []byte) (uint32, bool) { |
| 89 | offset := int(ins.Off) |
| 90 | size := int(ins.Size) |
| 91 | |
| 92 | return loadCommon(in, offset, size) |
| 93 | } |
| 94 | |
| 95 | func loadConstant(ins LoadConstant, regA uint32, regX uint32) (uint32, uint32) { |
| 96 | switch ins.Dst { |
| 97 | case RegA: |
| 98 | regA = ins.Val |
| 99 | case RegX: |
| 100 | regX = ins.Val |
| 101 | } |
| 102 | |
| 103 | return regA, regX |
| 104 | } |
| 105 | |
| 106 | func loadExtension(ins LoadExtension, in []byte) uint32 { |
| 107 | switch ins.Num { |
| 108 | case ExtLen: |
| 109 | return uint32(len(in)) |
| 110 | default: |
| 111 | panic(fmt.Sprintf("unimplemented extension: %d", ins.Num)) |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | func loadIndirect(ins LoadIndirect, in []byte, regX uint32) (uint32, bool) { |
| 116 | offset := int(ins.Off) + int(regX) |
| 117 | size := int(ins.Size) |
| 118 | |
| 119 | return loadCommon(in, offset, size) |
| 120 | } |
| 121 | |
| 122 | func loadMemShift(ins LoadMemShift, in []byte) (uint32, bool) { |
| 123 | offset := int(ins.Off) |
| 124 | |
| 125 | if !inBounds(len(in), offset, 0) { |
| 126 | return 0, false |
| 127 | } |
| 128 | |
| 129 | // Mask off high 4 bits and multiply low 4 bits by 4 |
| 130 | return uint32(in[offset]&0x0f) * 4, true |
| 131 | } |
| 132 | |
| 133 | func inBounds(inLen int, offset int, size int) bool { |
| 134 | return offset+size <= inLen |
| 135 | } |
| 136 | |
| 137 | func loadCommon(in []byte, offset int, size int) (uint32, bool) { |
| 138 | if !inBounds(len(in), offset, size) { |
| 139 | return 0, false |
| 140 | } |
| 141 | |
| 142 | switch size { |
| 143 | case 1: |
| 144 | return uint32(in[offset]), true |
| 145 | case 2: |
| 146 | return uint32(binary.BigEndian.Uint16(in[offset : offset+size])), true |
| 147 | case 4: |
| 148 | return uint32(binary.BigEndian.Uint32(in[offset : offset+size])), true |
| 149 | default: |
| 150 | panic(fmt.Sprintf("invalid load size: %d", size)) |
| 151 | } |
| 152 | } |
| 153 | |
| 154 | func loadScratch(ins LoadScratch, regScratch [16]uint32, regA uint32, regX uint32) (uint32, uint32) { |
| 155 | switch ins.Dst { |
| 156 | case RegA: |
| 157 | regA = regScratch[ins.N] |
| 158 | case RegX: |
| 159 | regX = regScratch[ins.N] |
| 160 | } |
| 161 | |
| 162 | return regA, regX |
| 163 | } |
| 164 | |
| 165 | func storeScratch(ins StoreScratch, regScratch [16]uint32, regA uint32, regX uint32) [16]uint32 { |
| 166 | switch ins.Src { |
| 167 | case RegA: |
| 168 | regScratch[ins.N] = regA |
| 169 | case RegX: |
| 170 | regScratch[ins.N] = regX |
| 171 | } |
| 172 | |
| 173 | return regScratch |
| 174 | } |