syncthing/vendor/golang.org/x/net/bpf/instructions.go
2016-09-13 21:56:33 +02:00

435 lines
9.9 KiB
Go

// 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 "fmt"
// An Instruction is one instruction executed by the BPF virtual
// machine.
type Instruction interface {
// Assemble assembles the Instruction into a RawInstruction.
Assemble() (RawInstruction, error)
}
// A RawInstruction is a raw BPF virtual machine instruction.
type RawInstruction struct {
// Operation to execute.
Op uint16
// For conditional jump instructions, the number of instructions
// to skip if the condition is true/false.
Jt uint8
Jf uint8
// Constant parameter. The meaning depends on the Op.
K uint32
}
// Assemble implements the Instruction Assemble method.
func (ri RawInstruction) Assemble() (RawInstruction, error) { return ri, nil }
// Disassemble parses ri into an Instruction and returns it. If ri is
// not recognized by this package, ri itself is returned.
func (ri RawInstruction) Disassemble() Instruction {
switch ri.Op & opMaskCls {
case opClsLoadA, opClsLoadX:
reg := Register(ri.Op & opMaskLoadDest)
sz := 0
switch ri.Op & opMaskLoadWidth {
case opLoadWidth4:
sz = 4
case opLoadWidth2:
sz = 2
case opLoadWidth1:
sz = 1
default:
return ri
}
switch ri.Op & opMaskLoadMode {
case opAddrModeImmediate:
if sz != 4 {
return ri
}
return LoadConstant{Dst: reg, Val: ri.K}
case opAddrModeScratch:
if sz != 4 || ri.K > 15 {
return ri
}
return LoadScratch{Dst: reg, N: int(ri.K)}
case opAddrModeAbsolute:
return LoadAbsolute{Size: sz, Off: ri.K}
case opAddrModeIndirect:
return LoadIndirect{Size: sz, Off: ri.K}
case opAddrModePacketLen:
if sz != 4 {
return ri
}
return LoadExtension{Num: ExtLen}
case opAddrModeMemShift:
return LoadMemShift{Off: ri.K}
default:
return ri
}
case opClsStoreA:
if ri.Op != opClsStoreA || ri.K > 15 {
return ri
}
return StoreScratch{Src: RegA, N: int(ri.K)}
case opClsStoreX:
if ri.Op != opClsStoreX || ri.K > 15 {
return ri
}
return StoreScratch{Src: RegX, N: int(ri.K)}
case opClsALU:
switch op := ALUOp(ri.Op & opMaskOperator); op {
case ALUOpAdd, ALUOpSub, ALUOpMul, ALUOpDiv, ALUOpOr, ALUOpAnd, ALUOpShiftLeft, ALUOpShiftRight, ALUOpMod, ALUOpXor:
if ri.Op&opMaskOperandSrc != 0 {
return ALUOpX{Op: op}
}
return ALUOpConstant{Op: op, Val: ri.K}
case aluOpNeg:
return NegateA{}
default:
return ri
}
case opClsJump:
if ri.Op&opMaskJumpConst != opClsJump {
return ri
}
switch ri.Op & opMaskJumpCond {
case opJumpAlways:
return Jump{Skip: ri.K}
case opJumpEqual:
return JumpIf{
Cond: JumpEqual,
Val: ri.K,
SkipTrue: ri.Jt,
SkipFalse: ri.Jf,
}
case opJumpGT:
return JumpIf{
Cond: JumpGreaterThan,
Val: ri.K,
SkipTrue: ri.Jt,
SkipFalse: ri.Jf,
}
case opJumpGE:
return JumpIf{
Cond: JumpGreaterOrEqual,
Val: ri.K,
SkipTrue: ri.Jt,
SkipFalse: ri.Jf,
}
case opJumpSet:
return JumpIf{
Cond: JumpBitsSet,
Val: ri.K,
SkipTrue: ri.Jt,
SkipFalse: ri.Jf,
}
default:
return ri
}
case opClsReturn:
switch ri.Op {
case opClsReturn | opRetSrcA:
return RetA{}
case opClsReturn | opRetSrcConstant:
return RetConstant{Val: ri.K}
default:
return ri
}
case opClsMisc:
switch ri.Op {
case opClsMisc | opMiscTAX:
return TAX{}
case opClsMisc | opMiscTXA:
return TXA{}
default:
return ri
}
default:
panic("unreachable") // switch is exhaustive on the bit pattern
}
}
// LoadConstant loads Val into register Dst.
type LoadConstant struct {
Dst Register
Val uint32
}
// Assemble implements the Instruction Assemble method.
func (a LoadConstant) Assemble() (RawInstruction, error) {
return assembleLoad(a.Dst, 4, opAddrModeImmediate, a.Val)
}
// LoadScratch loads scratch[N] into register Dst.
type LoadScratch struct {
Dst Register
N int // 0-15
}
// Assemble implements the Instruction Assemble method.
func (a LoadScratch) Assemble() (RawInstruction, error) {
if a.N < 0 || a.N > 15 {
return RawInstruction{}, fmt.Errorf("invalid scratch slot %d", a.N)
}
return assembleLoad(a.Dst, 4, opAddrModeScratch, uint32(a.N))
}
// LoadAbsolute loads packet[Off:Off+Size] as an integer value into
// register A.
type LoadAbsolute struct {
Off uint32
Size int // 1, 2 or 4
}
// Assemble implements the Instruction Assemble method.
func (a LoadAbsolute) Assemble() (RawInstruction, error) {
return assembleLoad(RegA, a.Size, opAddrModeAbsolute, a.Off)
}
// LoadIndirect loads packet[X+Off:X+Off+Size] as an integer value
// into register A.
type LoadIndirect struct {
Off uint32
Size int // 1, 2 or 4
}
// Assemble implements the Instruction Assemble method.
func (a LoadIndirect) Assemble() (RawInstruction, error) {
return assembleLoad(RegA, a.Size, opAddrModeIndirect, a.Off)
}
// LoadMemShift multiplies the first 4 bits of the byte at packet[Off]
// by 4 and stores the result in register X.
//
// This instruction is mainly useful to load into X the length of an
// IPv4 packet header in a single instruction, rather than have to do
// the arithmetic on the header's first byte by hand.
type LoadMemShift struct {
Off uint32
}
// Assemble implements the Instruction Assemble method.
func (a LoadMemShift) Assemble() (RawInstruction, error) {
return assembleLoad(RegX, 1, opAddrModeMemShift, a.Off)
}
// LoadExtension invokes a linux-specific extension and stores the
// result in register A.
type LoadExtension struct {
Num Extension
}
// Assemble implements the Instruction Assemble method.
func (a LoadExtension) Assemble() (RawInstruction, error) {
if a.Num == ExtLen {
return assembleLoad(RegA, 4, opAddrModePacketLen, 0)
}
return assembleLoad(RegA, 4, opAddrModeAbsolute, uint32(-0x1000+a.Num))
}
// StoreScratch stores register Src into scratch[N].
type StoreScratch struct {
Src Register
N int // 0-15
}
// Assemble implements the Instruction Assemble method.
func (a StoreScratch) Assemble() (RawInstruction, error) {
if a.N < 0 || a.N > 15 {
return RawInstruction{}, fmt.Errorf("invalid scratch slot %d", a.N)
}
var op uint16
switch a.Src {
case RegA:
op = opClsStoreA
case RegX:
op = opClsStoreX
default:
return RawInstruction{}, fmt.Errorf("invalid source register %v", a.Src)
}
return RawInstruction{
Op: op,
K: uint32(a.N),
}, nil
}
// ALUOpConstant executes A = A <Op> Val.
type ALUOpConstant struct {
Op ALUOp
Val uint32
}
// Assemble implements the Instruction Assemble method.
func (a ALUOpConstant) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsALU | opALUSrcConstant | uint16(a.Op),
K: a.Val,
}, nil
}
// ALUOpX executes A = A <Op> X
type ALUOpX struct {
Op ALUOp
}
// Assemble implements the Instruction Assemble method.
func (a ALUOpX) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsALU | opALUSrcX | uint16(a.Op),
}, nil
}
// NegateA executes A = -A.
type NegateA struct{}
// Assemble implements the Instruction Assemble method.
func (a NegateA) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsALU | uint16(aluOpNeg),
}, nil
}
// Jump skips the following Skip instructions in the program.
type Jump struct {
Skip uint32
}
// Assemble implements the Instruction Assemble method.
func (a Jump) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsJump | opJumpAlways,
K: a.Skip,
}, nil
}
// JumpIf skips the following Skip instructions in the program if A
// <Cond> Val is true.
type JumpIf struct {
Cond JumpTest
Val uint32
SkipTrue uint8
SkipFalse uint8
}
// Assemble implements the Instruction Assemble method.
func (a JumpIf) Assemble() (RawInstruction, error) {
var (
cond uint16
flip bool
)
switch a.Cond {
case JumpEqual:
cond = opJumpEqual
case JumpNotEqual:
cond, flip = opJumpEqual, true
case JumpGreaterThan:
cond = opJumpGT
case JumpLessThan:
cond, flip = opJumpGE, true
case JumpGreaterOrEqual:
cond = opJumpGE
case JumpLessOrEqual:
cond, flip = opJumpGT, true
case JumpBitsSet:
cond = opJumpSet
case JumpBitsNotSet:
cond, flip = opJumpSet, true
default:
return RawInstruction{}, fmt.Errorf("unknown JumpTest %v", a.Cond)
}
jt, jf := a.SkipTrue, a.SkipFalse
if flip {
jt, jf = jf, jt
}
return RawInstruction{
Op: opClsJump | cond,
Jt: jt,
Jf: jf,
K: a.Val,
}, nil
}
// RetA exits the BPF program, returning the value of register A.
type RetA struct{}
// Assemble implements the Instruction Assemble method.
func (a RetA) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsReturn | opRetSrcA,
}, nil
}
// RetConstant exits the BPF program, returning a constant value.
type RetConstant struct {
Val uint32
}
// Assemble implements the Instruction Assemble method.
func (a RetConstant) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsReturn | opRetSrcConstant,
K: a.Val,
}, nil
}
// TXA copies the value of register X to register A.
type TXA struct{}
// Assemble implements the Instruction Assemble method.
func (a TXA) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsMisc | opMiscTXA,
}, nil
}
// TAX copies the value of register A to register X.
type TAX struct{}
// Assemble implements the Instruction Assemble method.
func (a TAX) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsMisc | opMiscTAX,
}, nil
}
func assembleLoad(dst Register, loadSize int, mode uint16, k uint32) (RawInstruction, error) {
var (
cls uint16
sz uint16
)
switch dst {
case RegA:
cls = opClsLoadA
case RegX:
cls = opClsLoadX
default:
return RawInstruction{}, fmt.Errorf("invalid target register %v", dst)
}
switch loadSize {
case 1:
sz = opLoadWidth1
case 2:
sz = opLoadWidth2
case 4:
sz = opLoadWidth4
default:
return RawInstruction{}, fmt.Errorf("invalid load byte length %d", sz)
}
return RawInstruction{
Op: cls | sz | mode,
K: k,
}, nil
}