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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"
// Assemble converts insts into raw instructions suitable for loading
// into a BPF virtual machine.
//
// Currently, no optimization is attempted, the assembled program flow
// is exactly as provided.
func Assemble(insts []Instruction) ([]RawInstruction, error) {
ret := make([]RawInstruction, len(insts))
var err error
for i, inst := range insts {
ret[i], err = inst.Assemble()
if err != nil {
return nil, fmt.Errorf("assembling instruction %d: %s", i+1, err)
}
}
return ret, nil
}
// Disassemble attempts to parse raw back into
// Instructions. Unrecognized RawInstructions are assumed to be an
// extension not implemented by this package, and are passed through
// unchanged to the output. The allDecoded value reports whether insts
// contains no RawInstructions.
func Disassemble(raw []RawInstruction) (insts []Instruction, allDecoded bool) {
insts = make([]Instruction, len(raw))
allDecoded = true
for i, r := range raw {
insts[i] = r.Disassemble()
if _, ok := insts[i].(RawInstruction); ok {
allDecoded = false
}
}
return insts, allDecoded
}

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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
// A Register is a register of the BPF virtual machine.
type Register uint16
const (
// RegA is the accumulator register. RegA is always the
// destination register of ALU operations.
RegA Register = iota
// RegX is the indirection register, used by LoadIndirect
// operations.
RegX
)
// An ALUOp is an arithmetic or logic operation.
type ALUOp uint16
// ALU binary operation types.
const (
ALUOpAdd ALUOp = iota << 4
ALUOpSub
ALUOpMul
ALUOpDiv
ALUOpOr
ALUOpAnd
ALUOpShiftLeft
ALUOpShiftRight
aluOpNeg // Not exported because it's the only unary ALU operation, and gets its own instruction type.
ALUOpMod
ALUOpXor
)
// A JumpTest is a comparison operator used in conditional jumps.
type JumpTest uint16
// Supported operators for conditional jumps.
// K can be RegX for JumpIfX
const (
// K == A
JumpEqual JumpTest = iota
// K != A
JumpNotEqual
// K > A
JumpGreaterThan
// K < A
JumpLessThan
// K >= A
JumpGreaterOrEqual
// K <= A
JumpLessOrEqual
// K & A != 0
JumpBitsSet
// K & A == 0
JumpBitsNotSet
)
// An Extension is a function call provided by the kernel that
// performs advanced operations that are expensive or impossible
// within the BPF virtual machine.
//
// Extensions are only implemented by the Linux kernel.
//
// TODO: should we prune this list? Some of these extensions seem
// either broken or near-impossible to use correctly, whereas other
// (len, random, ifindex) are quite useful.
type Extension int
// Extension functions available in the Linux kernel.
const (
// extOffset is the negative maximum number of instructions used
// to load instructions by overloading the K argument.
extOffset = -0x1000
// ExtLen returns the length of the packet.
ExtLen Extension = 1
// ExtProto returns the packet's L3 protocol type.
ExtProto Extension = 0
// ExtType returns the packet's type (skb->pkt_type in the kernel)
//
// TODO: better documentation. How nice an API do we want to
// provide for these esoteric extensions?
ExtType Extension = 4
// ExtPayloadOffset returns the offset of the packet payload, or
// the first protocol header that the kernel does not know how to
// parse.
ExtPayloadOffset Extension = 52
// ExtInterfaceIndex returns the index of the interface on which
// the packet was received.
ExtInterfaceIndex Extension = 8
// ExtNetlinkAttr returns the netlink attribute of type X at
// offset A.
ExtNetlinkAttr Extension = 12
// ExtNetlinkAttrNested returns the nested netlink attribute of
// type X at offset A.
ExtNetlinkAttrNested Extension = 16
// ExtMark returns the packet's mark value.
ExtMark Extension = 20
// ExtQueue returns the packet's assigned hardware queue.
ExtQueue Extension = 24
// ExtLinkLayerType returns the packet's hardware address type
// (e.g. Ethernet, Infiniband).
ExtLinkLayerType Extension = 28
// ExtRXHash returns the packets receive hash.
//
// TODO: figure out what this rxhash actually is.
ExtRXHash Extension = 32
// ExtCPUID returns the ID of the CPU processing the current
// packet.
ExtCPUID Extension = 36
// ExtVLANTag returns the packet's VLAN tag.
ExtVLANTag Extension = 44
// ExtVLANTagPresent returns non-zero if the packet has a VLAN
// tag.
//
// TODO: I think this might be a lie: it reads bit 0x1000 of the
// VLAN header, which changed meaning in recent revisions of the
// spec - this extension may now return meaningless information.
ExtVLANTagPresent Extension = 48
// ExtVLANProto returns 0x8100 if the frame has a VLAN header,
// 0x88a8 if the frame has a "Q-in-Q" double VLAN header, or some
// other value if no VLAN information is present.
ExtVLANProto Extension = 60
// ExtRand returns a uniformly random uint32.
ExtRand Extension = 56
)
// The following gives names to various bit patterns used in opcode construction.
const (
opMaskCls uint16 = 0x7
// opClsLoad masks
opMaskLoadDest = 0x01
opMaskLoadWidth = 0x18
opMaskLoadMode = 0xe0
// opClsALU & opClsJump
opMaskOperand = 0x08
opMaskOperator = 0xf0
)
const (
// +---------------+-----------------+---+---+---+
// | AddrMode (3b) | LoadWidth (2b) | 0 | 0 | 0 |
// +---------------+-----------------+---+---+---+
opClsLoadA uint16 = iota
// +---------------+-----------------+---+---+---+
// | AddrMode (3b) | LoadWidth (2b) | 0 | 0 | 1 |
// +---------------+-----------------+---+---+---+
opClsLoadX
// +---+---+---+---+---+---+---+---+
// | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
// +---+---+---+---+---+---+---+---+
opClsStoreA
// +---+---+---+---+---+---+---+---+
// | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
// +---+---+---+---+---+---+---+---+
opClsStoreX
// +---------------+-----------------+---+---+---+
// | Operator (4b) | OperandSrc (1b) | 1 | 0 | 0 |
// +---------------+-----------------+---+---+---+
opClsALU
// +-----------------------------+---+---+---+---+
// | TestOperator (4b) | 0 | 1 | 0 | 1 |
// +-----------------------------+---+---+---+---+
opClsJump
// +---+-------------------------+---+---+---+---+
// | 0 | 0 | 0 | RetSrc (1b) | 0 | 1 | 1 | 0 |
// +---+-------------------------+---+---+---+---+
opClsReturn
// +---+-------------------------+---+---+---+---+
// | 0 | 0 | 0 | TXAorTAX (1b) | 0 | 1 | 1 | 1 |
// +---+-------------------------+---+---+---+---+
opClsMisc
)
const (
opAddrModeImmediate uint16 = iota << 5
opAddrModeAbsolute
opAddrModeIndirect
opAddrModeScratch
opAddrModePacketLen // actually an extension, not an addressing mode.
opAddrModeMemShift
)
const (
opLoadWidth4 uint16 = iota << 3
opLoadWidth2
opLoadWidth1
)
// Operand for ALU and Jump instructions
type opOperand uint16
// Supported operand sources.
const (
opOperandConstant opOperand = iota << 3
opOperandX
)
// An jumpOp is a conditional jump condition.
type jumpOp uint16
// Supported jump conditions.
const (
opJumpAlways jumpOp = iota << 4
opJumpEqual
opJumpGT
opJumpGE
opJumpSet
)
const (
opRetSrcConstant uint16 = iota << 4
opRetSrcA
)
const (
opMiscTAX = 0x00
opMiscTXA = 0x80
)

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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 implements marshaling and unmarshaling of programs for the
Berkeley Packet Filter virtual machine, and provides a Go implementation
of the virtual machine.
BPF's main use is to specify a packet filter for network taps, so that
the kernel doesn't have to expensively copy every packet it sees to
userspace. However, it's been repurposed to other areas where running
user code in-kernel is needed. For example, Linux's seccomp uses BPF
to apply security policies to system calls. For simplicity, this
documentation refers only to packets, but other uses of BPF have their
own data payloads.
BPF programs run in a restricted virtual machine. It has almost no
access to kernel functions, and while conditional branches are
allowed, they can only jump forwards, to guarantee that there are no
infinite loops.
# The virtual machine
The BPF VM is an accumulator machine. Its main register, called
register A, is an implicit source and destination in all arithmetic
and logic operations. The machine also has 16 scratch registers for
temporary storage, and an indirection register (register X) for
indirect memory access. All registers are 32 bits wide.
Each run of a BPF program is given one packet, which is placed in the
VM's read-only "main memory". LoadAbsolute and LoadIndirect
instructions can fetch up to 32 bits at a time into register A for
examination.
The goal of a BPF program is to produce and return a verdict (uint32),
which tells the kernel what to do with the packet. In the context of
packet filtering, the returned value is the number of bytes of the
packet to forward to userspace, or 0 to ignore the packet. Other
contexts like seccomp define their own return values.
In order to simplify programs, attempts to read past the end of the
packet terminate the program execution with a verdict of 0 (ignore
packet). This means that the vast majority of BPF programs don't need
to do any explicit bounds checking.
In addition to the bytes of the packet, some BPF programs have access
to extensions, which are essentially calls to kernel utility
functions. Currently, the only extensions supported by this package
are the Linux packet filter extensions.
# Examples
This packet filter selects all ARP packets.
bpf.Assemble([]bpf.Instruction{
// Load "EtherType" field from the ethernet header.
bpf.LoadAbsolute{Off: 12, Size: 2},
// Skip over the next instruction if EtherType is not ARP.
bpf.JumpIf{Cond: bpf.JumpNotEqual, Val: 0x0806, SkipTrue: 1},
// Verdict is "send up to 4k of the packet to userspace."
bpf.RetConstant{Val: 4096},
// Verdict is "ignore packet."
bpf.RetConstant{Val: 0},
})
This packet filter captures a random 1% sample of traffic.
bpf.Assemble([]bpf.Instruction{
// Get a 32-bit random number from the Linux kernel.
bpf.LoadExtension{Num: bpf.ExtRand},
// 1% dice roll?
bpf.JumpIf{Cond: bpf.JumpLessThan, Val: 2^32/100, SkipFalse: 1},
// Capture.
bpf.RetConstant{Val: 4096},
// Ignore.
bpf.RetConstant{Val: 0},
})
*/
package bpf // import "golang.org/x/net/bpf"

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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 <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 | 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 <Op> 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
// <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) {
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
// <Cond> 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
}

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vendor/golang.org/x/net/bpf/setter.go generated vendored Normal file
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// Copyright 2017 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
// A Setter is a type which can attach a compiled BPF filter to itself.
type Setter interface {
SetBPF(filter []RawInstruction) error
}

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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)
}
case JumpIfX:
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 JumpIfX:
jump := jumpIfX(ins, regA, regX)
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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vendor/golang.org/x/net/bpf/vm_instructions.go generated vendored Normal file
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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 (
"encoding/binary"
"fmt"
)
func aluOpConstant(ins ALUOpConstant, regA uint32) uint32 {
return aluOpCommon(ins.Op, regA, ins.Val)
}
func aluOpX(ins ALUOpX, regA uint32, regX uint32) (uint32, bool) {
// Guard against division or modulus by zero by terminating
// the program, as the OS BPF VM does
if regX == 0 {
switch ins.Op {
case ALUOpDiv, ALUOpMod:
return 0, false
}
}
return aluOpCommon(ins.Op, regA, regX), true
}
func aluOpCommon(op ALUOp, regA uint32, value uint32) uint32 {
switch op {
case ALUOpAdd:
return regA + value
case ALUOpSub:
return regA - value
case ALUOpMul:
return regA * value
case ALUOpDiv:
// Division by zero not permitted by NewVM and aluOpX checks
return regA / value
case ALUOpOr:
return regA | value
case ALUOpAnd:
return regA & value
case ALUOpShiftLeft:
return regA << value
case ALUOpShiftRight:
return regA >> value
case ALUOpMod:
// Modulus by zero not permitted by NewVM and aluOpX checks
return regA % value
case ALUOpXor:
return regA ^ value
default:
return regA
}
}
func jumpIf(ins JumpIf, regA uint32) int {
return jumpIfCommon(ins.Cond, ins.SkipTrue, ins.SkipFalse, regA, ins.Val)
}
func jumpIfX(ins JumpIfX, regA uint32, regX uint32) int {
return jumpIfCommon(ins.Cond, ins.SkipTrue, ins.SkipFalse, regA, regX)
}
func jumpIfCommon(cond JumpTest, skipTrue, skipFalse uint8, regA uint32, value uint32) int {
var ok bool
switch cond {
case JumpEqual:
ok = regA == value
case JumpNotEqual:
ok = regA != value
case JumpGreaterThan:
ok = regA > value
case JumpLessThan:
ok = regA < value
case JumpGreaterOrEqual:
ok = regA >= value
case JumpLessOrEqual:
ok = regA <= value
case JumpBitsSet:
ok = (regA & value) != 0
case JumpBitsNotSet:
ok = (regA & value) == 0
}
if ok {
return int(skipTrue)
}
return int(skipFalse)
}
func loadAbsolute(ins LoadAbsolute, in []byte) (uint32, bool) {
offset := int(ins.Off)
size := ins.Size
return loadCommon(in, offset, size)
}
func loadConstant(ins LoadConstant, regA uint32, regX uint32) (uint32, uint32) {
switch ins.Dst {
case RegA:
regA = ins.Val
case RegX:
regX = ins.Val
}
return regA, regX
}
func loadExtension(ins LoadExtension, in []byte) uint32 {
switch ins.Num {
case ExtLen:
return uint32(len(in))
default:
panic(fmt.Sprintf("unimplemented extension: %d", ins.Num))
}
}
func loadIndirect(ins LoadIndirect, in []byte, regX uint32) (uint32, bool) {
offset := int(ins.Off) + int(regX)
size := ins.Size
return loadCommon(in, offset, size)
}
func loadMemShift(ins LoadMemShift, in []byte) (uint32, bool) {
offset := int(ins.Off)
// Size of LoadMemShift is always 1 byte
if !inBounds(len(in), offset, 1) {
return 0, false
}
// Mask off high 4 bits and multiply low 4 bits by 4
return uint32(in[offset]&0x0f) * 4, true
}
func inBounds(inLen int, offset int, size int) bool {
return offset+size <= inLen
}
func loadCommon(in []byte, offset int, size int) (uint32, bool) {
if !inBounds(len(in), offset, size) {
return 0, false
}
switch size {
case 1:
return uint32(in[offset]), true
case 2:
return uint32(binary.BigEndian.Uint16(in[offset : offset+size])), true
case 4:
return uint32(binary.BigEndian.Uint32(in[offset : offset+size])), true
default:
panic(fmt.Sprintf("invalid load size: %d", size))
}
}
func loadScratch(ins LoadScratch, regScratch [16]uint32, regA uint32, regX uint32) (uint32, uint32) {
switch ins.Dst {
case RegA:
regA = regScratch[ins.N]
case RegX:
regX = regScratch[ins.N]
}
return regA, regX
}
func storeScratch(ins StoreScratch, regScratch [16]uint32, regA uint32, regX uint32) [16]uint32 {
switch ins.Src {
case RegA:
regScratch[ins.N] = regA
case RegX:
regScratch[ins.N] = regX
}
return regScratch
}