+++ /dev/null
-// 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
-}
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