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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 "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:
if ri.K > extOffset+0xffffffff {
return LoadExtension{Num: Extension(-extOffset + ri.K)}
}
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:
switch operand := opOperand(ri.Op & opMaskOperand); operand {
case opOperandX:
return ALUOpX{Op: op}
case opOperandConstant:
return ALUOpConstant{Op: op, Val: ri.K}
default:
return ri
}
case aluOpNeg:
return NegateA{}
default:
return ri
}
case opClsJump:
switch op := jumpOp(ri.Op & opMaskOperator); op {
case opJumpAlways:
return Jump{Skip: ri.K}
case opJumpEqual, opJumpGT, opJumpGE, opJumpSet:
cond, skipTrue, skipFalse := jumpOpToTest(op, ri.Jt, ri.Jf)
switch operand := opOperand(ri.Op & opMaskOperand); operand {
case opOperandX:
return JumpIfX{Cond: cond, SkipTrue: skipTrue, SkipFalse: skipFalse}
case opOperandConstant:
return JumpIf{Cond: cond, Val: ri.K, SkipTrue: skipTrue, SkipFalse: skipFalse}
default:
return ri
}
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
}
}
func jumpOpToTest(op jumpOp, skipTrue uint8, skipFalse uint8) (JumpTest, uint8, uint8) {
var test JumpTest
// Decode "fake" jump conditions that don't appear in machine code
// Ensures the Assemble -> Disassemble stage recreates the same instructions
// See https://github.com/golang/go/issues/18470
if skipTrue == 0 {
switch op {
case opJumpEqual:
test = JumpNotEqual
case opJumpGT:
test = JumpLessOrEqual
case opJumpGE:
test = JumpLessThan
case opJumpSet:
test = JumpBitsNotSet
}
return test, skipFalse, 0
}
switch op {
case opJumpEqual:
test = JumpEqual
case opJumpGT:
test = JumpGreaterThan
case opJumpGE:
test = JumpGreaterOrEqual
case opJumpSet:
test = JumpBitsSet
}
return test, skipTrue, skipFalse
}
// 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)
}
// String returns the instruction in assembler notation.
func (a LoadConstant) String() string {
switch a.Dst {
case RegA:
return fmt.Sprintf("ld #%d", a.Val)
case RegX:
return fmt.Sprintf("ldx #%d", a.Val)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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))
}
// String returns the instruction in assembler notation.
func (a LoadScratch) String() string {
switch a.Dst {
case RegA:
return fmt.Sprintf("ld M[%d]", a.N)
case RegX:
return fmt.Sprintf("ldx M[%d]", a.N)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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)
}
// String returns the instruction in assembler notation.
func (a LoadAbsolute) String() string {
switch a.Size {
case 1: // byte
return fmt.Sprintf("ldb [%d]", a.Off)
case 2: // half word
return fmt.Sprintf("ldh [%d]", a.Off)
case 4: // word
if a.Off > extOffset+0xffffffff {
return LoadExtension{Num: Extension(a.Off + 0x1000)}.String()
}
return fmt.Sprintf("ld [%d]", a.Off)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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)
}
// String returns the instruction in assembler notation.
func (a LoadIndirect) String() string {
switch a.Size {
case 1: // byte
return fmt.Sprintf("ldb [x + %d]", a.Off)
case 2: // half word
return fmt.Sprintf("ldh [x + %d]", a.Off)
case 4: // word
return fmt.Sprintf("ld [x + %d]", a.Off)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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)
}
// String returns the instruction in assembler notation.
func (a LoadMemShift) String() string {
return fmt.Sprintf("ldx 4*([%d]&0xf)", 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(extOffset+a.Num))
}
// String returns the instruction in assembler notation.
func (a LoadExtension) String() string {
switch a.Num {
case ExtLen:
return "ld #len"
case ExtProto:
return "ld #proto"
case ExtType:
return "ld #type"
case ExtPayloadOffset:
return "ld #poff"
case ExtInterfaceIndex:
return "ld #ifidx"
case ExtNetlinkAttr:
return "ld #nla"
case ExtNetlinkAttrNested:
return "ld #nlan"
case ExtMark:
return "ld #mark"
case ExtQueue:
return "ld #queue"
case ExtLinkLayerType:
return "ld #hatype"
case ExtRXHash:
return "ld #rxhash"
case ExtCPUID:
return "ld #cpu"
case ExtVLANTag:
return "ld #vlan_tci"
case ExtVLANTagPresent:
return "ld #vlan_avail"
case ExtVLANProto:
return "ld #vlan_tpid"
case ExtRand:
return "ld #rand"
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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
}
// String returns the instruction in assembler notation.
func (a StoreScratch) String() string {
switch a.Src {
case RegA:
return fmt.Sprintf("st M[%d]", a.N)
case RegX:
return fmt.Sprintf("stx M[%d]", a.N)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// ALUOpConstant executes A = A Val.
type ALUOpConstant struct {
Op ALUOp
Val uint32
}
// Assemble implements the Instruction Assemble method.
func (a ALUOpConstant) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsALU | uint16(opOperandConstant) | uint16(a.Op),
K: a.Val,
}, nil
}
// String returns the instruction in assembler notation.
func (a ALUOpConstant) String() string {
switch a.Op {
case ALUOpAdd:
return fmt.Sprintf("add #%d", a.Val)
case ALUOpSub:
return fmt.Sprintf("sub #%d", a.Val)
case ALUOpMul:
return fmt.Sprintf("mul #%d", a.Val)
case ALUOpDiv:
return fmt.Sprintf("div #%d", a.Val)
case ALUOpMod:
return fmt.Sprintf("mod #%d", a.Val)
case ALUOpAnd:
return fmt.Sprintf("and #%d", a.Val)
case ALUOpOr:
return fmt.Sprintf("or #%d", a.Val)
case ALUOpXor:
return fmt.Sprintf("xor #%d", a.Val)
case ALUOpShiftLeft:
return fmt.Sprintf("lsh #%d", a.Val)
case ALUOpShiftRight:
return fmt.Sprintf("rsh #%d", a.Val)
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// ALUOpX executes A = A X
type ALUOpX struct {
Op ALUOp
}
// Assemble implements the Instruction Assemble method.
func (a ALUOpX) Assemble() (RawInstruction, error) {
return RawInstruction{
Op: opClsALU | uint16(opOperandX) | uint16(a.Op),
}, nil
}
// String returns the instruction in assembler notation.
func (a ALUOpX) String() string {
switch a.Op {
case ALUOpAdd:
return "add x"
case ALUOpSub:
return "sub x"
case ALUOpMul:
return "mul x"
case ALUOpDiv:
return "div x"
case ALUOpMod:
return "mod x"
case ALUOpAnd:
return "and x"
case ALUOpOr:
return "or x"
case ALUOpXor:
return "xor x"
case ALUOpShiftLeft:
return "lsh x"
case ALUOpShiftRight:
return "rsh x"
default:
return fmt.Sprintf("unknown instruction: %#v", a)
}
}
// 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
}
// String returns the instruction in assembler notation.
func (a NegateA) String() string {
return fmt.Sprintf("neg")
}
// 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 | uint16(opJumpAlways),
K: a.Skip,
}, nil
}
// String returns the instruction in assembler notation.
func (a Jump) String() string {
return fmt.Sprintf("ja %d", a.Skip)
}
// JumpIf skips the following Skip instructions in the program if A
// 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) {
return jumpToRaw(a.Cond, opOperandConstant, a.Val, a.SkipTrue, a.SkipFalse)
}
// String returns the instruction in assembler notation.
func (a JumpIf) String() string {
return jumpToString(a.Cond, fmt.Sprintf("#%d", a.Val), a.SkipTrue, a.SkipFalse)
}
// JumpIfX skips the following Skip instructions in the program if A
// X is true.
type JumpIfX struct {
Cond JumpTest
SkipTrue uint8
SkipFalse uint8
}
// Assemble implements the Instruction Assemble method.
func (a JumpIfX) Assemble() (RawInstruction, error) {
return jumpToRaw(a.Cond, opOperandX, 0, a.SkipTrue, a.SkipFalse)
}
// String returns the instruction in assembler notation.
func (a JumpIfX) String() string {
return jumpToString(a.Cond, "x", a.SkipTrue, a.SkipFalse)
}
// jumpToRaw assembles a jump instruction into a RawInstruction
func jumpToRaw(test JumpTest, operand opOperand, k uint32, skipTrue, skipFalse uint8) (RawInstruction, error) {
var (
cond jumpOp
flip bool
)
switch test {
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", test)
}
jt, jf := skipTrue, skipFalse
if flip {
jt, jf = jf, jt
}
return RawInstruction{
Op: opClsJump | uint16(cond) | uint16(operand),
Jt: jt,
Jf: jf,
K: k,
}, nil
}
// jumpToString converts a jump instruction to assembler notation
func jumpToString(cond JumpTest, operand string, skipTrue, skipFalse uint8) string {
switch cond {
// K == A
case JumpEqual:
return conditionalJump(operand, skipTrue, skipFalse, "jeq", "jneq")
// K != A
case JumpNotEqual:
return fmt.Sprintf("jneq %s,%d", operand, skipTrue)
// K > A
case JumpGreaterThan:
return conditionalJump(operand, skipTrue, skipFalse, "jgt", "jle")
// K < A
case JumpLessThan:
return fmt.Sprintf("jlt %s,%d", operand, skipTrue)
// K >= A
case JumpGreaterOrEqual:
return conditionalJump(operand, skipTrue, skipFalse, "jge", "jlt")
// K <= A
case JumpLessOrEqual:
return fmt.Sprintf("jle %s,%d", operand, skipTrue)
// K & A != 0
case JumpBitsSet:
if skipFalse > 0 {
return fmt.Sprintf("jset %s,%d,%d", operand, skipTrue, skipFalse)
}
return fmt.Sprintf("jset %s,%d", operand, skipTrue)
// K & A == 0, there is no assembler instruction for JumpBitNotSet, use JumpBitSet and invert skips
case JumpBitsNotSet:
return jumpToString(JumpBitsSet, operand, skipFalse, skipTrue)
default:
return fmt.Sprintf("unknown JumpTest %#v", cond)
}
}
func conditionalJump(operand string, skipTrue, skipFalse uint8, positiveJump, negativeJump string) string {
if skipTrue > 0 {
if skipFalse > 0 {
return fmt.Sprintf("%s %s,%d,%d", positiveJump, operand, skipTrue, skipFalse)
}
return fmt.Sprintf("%s %s,%d", positiveJump, operand, skipTrue)
}
return fmt.Sprintf("%s %s,%d", negativeJump, operand, skipFalse)
}
// 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
}
// String returns the instruction in assembler notation.
func (a RetA) String() string {
return fmt.Sprintf("ret a")
}
// 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
}
// String returns the instruction in assembler notation.
func (a RetConstant) String() string {
return fmt.Sprintf("ret #%d", a.Val)
}
// 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
}
// String returns the instruction in assembler notation.
func (a TXA) String() string {
return fmt.Sprintf("txa")
}
// 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
}
// String returns the instruction in assembler notation.
func (a TAX) String() string {
return fmt.Sprintf("tax")
}
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
}