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-rw-r--r--vendor/golang.org/x/net/bpf/vm.go140
1 files changed, 140 insertions, 0 deletions
diff --git a/vendor/golang.org/x/net/bpf/vm.go b/vendor/golang.org/x/net/bpf/vm.go
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+++ b/vendor/golang.org/x/net/bpf/vm.go
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+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package bpf
+
+import (
+ "errors"
+ "fmt"
+)
+
+// A VM is an emulated BPF virtual machine.
+type VM struct {
+ filter []Instruction
+}
+
+// NewVM returns a new VM using the input BPF program.
+func NewVM(filter []Instruction) (*VM, error) {
+ if len(filter) == 0 {
+ return nil, errors.New("one or more Instructions must be specified")
+ }
+
+ for i, ins := range filter {
+ check := len(filter) - (i + 1)
+ switch ins := ins.(type) {
+ // Check for out-of-bounds jumps in instructions
+ case Jump:
+ if check <= int(ins.Skip) {
+ return nil, fmt.Errorf("cannot jump %d instructions; jumping past program bounds", ins.Skip)
+ }
+ case JumpIf:
+ if check <= int(ins.SkipTrue) {
+ return nil, fmt.Errorf("cannot jump %d instructions in true case; jumping past program bounds", ins.SkipTrue)
+ }
+ if check <= int(ins.SkipFalse) {
+ return nil, fmt.Errorf("cannot jump %d instructions in false case; jumping past program bounds", ins.SkipFalse)
+ }
+ // Check for division or modulus by zero
+ case ALUOpConstant:
+ if ins.Val != 0 {
+ break
+ }
+
+ switch ins.Op {
+ case ALUOpDiv, ALUOpMod:
+ return nil, errors.New("cannot divide by zero using ALUOpConstant")
+ }
+ // Check for unknown extensions
+ case LoadExtension:
+ switch ins.Num {
+ case ExtLen:
+ default:
+ return nil, fmt.Errorf("extension %d not implemented", ins.Num)
+ }
+ }
+ }
+
+ // Make sure last instruction is a return instruction
+ switch filter[len(filter)-1].(type) {
+ case RetA, RetConstant:
+ default:
+ return nil, errors.New("BPF program must end with RetA or RetConstant")
+ }
+
+ // Though our VM works using disassembled instructions, we
+ // attempt to assemble the input filter anyway to ensure it is compatible
+ // with an operating system VM.
+ _, err := Assemble(filter)
+
+ return &VM{
+ filter: filter,
+ }, err
+}
+
+// Run runs the VM's BPF program against the input bytes.
+// Run returns the number of bytes accepted by the BPF program, and any errors
+// which occurred while processing the program.
+func (v *VM) Run(in []byte) (int, error) {
+ var (
+ // Registers of the virtual machine
+ regA uint32
+ regX uint32
+ regScratch [16]uint32
+
+ // OK is true if the program should continue processing the next
+ // instruction, or false if not, causing the loop to break
+ ok = true
+ )
+
+ // TODO(mdlayher): implement:
+ // - NegateA:
+ // - would require a change from uint32 registers to int32
+ // registers
+
+ // TODO(mdlayher): add interop tests that check signedness of ALU
+ // operations against kernel implementation, and make sure Go
+ // implementation matches behavior
+
+ for i := 0; i < len(v.filter) && ok; i++ {
+ ins := v.filter[i]
+
+ switch ins := ins.(type) {
+ case ALUOpConstant:
+ regA = aluOpConstant(ins, regA)
+ case ALUOpX:
+ regA, ok = aluOpX(ins, regA, regX)
+ case Jump:
+ i += int(ins.Skip)
+ case JumpIf:
+ jump := jumpIf(ins, regA)
+ i += jump
+ case LoadAbsolute:
+ regA, ok = loadAbsolute(ins, in)
+ case LoadConstant:
+ regA, regX = loadConstant(ins, regA, regX)
+ case LoadExtension:
+ regA = loadExtension(ins, in)
+ case LoadIndirect:
+ regA, ok = loadIndirect(ins, in, regX)
+ case LoadMemShift:
+ regX, ok = loadMemShift(ins, in)
+ case LoadScratch:
+ regA, regX = loadScratch(ins, regScratch, regA, regX)
+ case RetA:
+ return int(regA), nil
+ case RetConstant:
+ return int(ins.Val), nil
+ case StoreScratch:
+ regScratch = storeScratch(ins, regScratch, regA, regX)
+ case TAX:
+ regX = regA
+ case TXA:
+ regA = regX
+ default:
+ return 0, fmt.Errorf("unknown Instruction at index %d: %T", i, ins)
+ }
+ }
+
+ return 0, nil
+}