/
instruction.go
731 lines (608 loc) · 18.6 KB
/
instruction.go
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package asm
import (
"crypto/sha1"
"encoding/binary"
"encoding/hex"
"errors"
"fmt"
"io"
"math"
"strings"
"github.com/cilium/ebpf/internal/unix"
)
// InstructionSize is the size of a BPF instruction in bytes
const InstructionSize = 8
// RawInstructionOffset is an offset in units of raw BPF instructions.
type RawInstructionOffset uint64
var ErrUnsatisfiedMapReference = errors.New("unsatisfied map reference")
var ErrUnsatisfiedProgramReference = errors.New("unsatisfied program reference")
// Bytes returns the offset of an instruction in bytes.
func (rio RawInstructionOffset) Bytes() uint64 {
return uint64(rio) * InstructionSize
}
// Instruction is a single eBPF instruction.
type Instruction struct {
OpCode OpCode
Dst Register
Src Register
Offset int16
Constant int64
// Metadata contains optional metadata about this instruction
metadata *metadata
}
// WithSymbol marks the Instruction as a Symbol, which other Instructions
// can point to using corresponding calls to WithReference.
func (ins Instruction) WithSymbol(name string) Instruction {
if (ins.metadata != nil && ins.metadata.symbol == name) ||
(ins.metadata == nil && name == "") {
return ins
}
ins.metadata = ins.metadata.copy()
ins.metadata.symbol = name
return ins
}
// Sym creates a symbol.
//
// Deprecated: use WithSymbol instead.
func (ins Instruction) Sym(name string) Instruction {
return ins.WithSymbol(name)
}
// Symbol returns the value ins has been marked with using WithSymbol,
// otherwise returns an empty string. A symbol is often an Instruction
// at the start of a function body.
func (ins Instruction) Symbol() string {
if ins.metadata == nil {
return ""
}
return ins.metadata.symbol
}
// Unmarshal decodes a BPF instruction.
func (ins *Instruction) Unmarshal(r io.Reader, bo binary.ByteOrder) (uint64, error) {
data := make([]byte, InstructionSize)
if _, err := io.ReadFull(r, data); err != nil {
return 0, err
}
ins.OpCode = OpCode(data[0])
regs := data[1]
switch bo {
case binary.LittleEndian:
ins.Dst, ins.Src = Register(regs&0xF), Register(regs>>4)
case binary.BigEndian:
ins.Dst, ins.Src = Register(regs>>4), Register(regs&0xf)
}
ins.Offset = int16(bo.Uint16(data[2:4]))
// Convert to int32 before widening to int64
// to ensure the signed bit is carried over.
ins.Constant = int64(int32(bo.Uint32(data[4:8])))
if !ins.OpCode.IsDWordLoad() {
return InstructionSize, nil
}
// Pull another instruction from the stream to retrieve the second
// half of the 64-bit immediate value.
if _, err := io.ReadFull(r, data); err != nil {
// No Wrap, to avoid io.EOF clash
return 0, errors.New("64bit immediate is missing second half")
}
// Require that all fields other than the value are zero.
if bo.Uint32(data[0:4]) != 0 {
return 0, errors.New("64bit immediate has non-zero fields")
}
cons1 := uint32(ins.Constant)
cons2 := int32(bo.Uint32(data[4:8]))
ins.Constant = int64(cons2)<<32 | int64(cons1)
return 2 * InstructionSize, nil
}
// Marshal encodes a BPF instruction.
func (ins Instruction) Marshal(w io.Writer, bo binary.ByteOrder) (uint64, error) {
if ins.OpCode == InvalidOpCode {
return 0, errors.New("invalid opcode")
}
isDWordLoad := ins.OpCode.IsDWordLoad()
cons := int32(ins.Constant)
if isDWordLoad {
// Encode least significant 32bit first for 64bit operations.
cons = int32(uint32(ins.Constant))
}
regs, err := newBPFRegisters(ins.Dst, ins.Src, bo)
if err != nil {
return 0, fmt.Errorf("can't marshal registers: %s", err)
}
data := make([]byte, InstructionSize)
data[0] = byte(ins.OpCode)
data[1] = byte(regs)
bo.PutUint16(data[2:4], uint16(ins.Offset))
bo.PutUint32(data[4:8], uint32(cons))
if _, err := w.Write(data); err != nil {
return 0, err
}
if !isDWordLoad {
return InstructionSize, nil
}
// The first half of the second part of a double-wide instruction
// must be zero. The second half carries the value.
bo.PutUint32(data[0:4], 0)
bo.PutUint32(data[4:8], uint32(ins.Constant>>32))
if _, err := w.Write(data); err != nil {
return 0, err
}
return 2 * InstructionSize, nil
}
// RewriteMapPtr changes an instruction to use a new map fd.
//
// Returns an error if the instruction doesn't load a map.
func (ins *Instruction) RewriteMapPtr(fd int) error {
if !ins.OpCode.IsDWordLoad() {
return fmt.Errorf("%s is not a 64 bit load", ins.OpCode)
}
if ins.Src != PseudoMapFD && ins.Src != PseudoMapValue {
return errors.New("not a load from a map")
}
// Preserve the offset value for direct map loads.
offset := uint64(ins.Constant) & (math.MaxUint32 << 32)
rawFd := uint64(uint32(fd))
ins.Constant = int64(offset | rawFd)
return nil
}
// MapPtr returns the map fd for this instruction.
//
// The result is undefined if the instruction is not a load from a map,
// see IsLoadFromMap.
func (ins *Instruction) MapPtr() int {
return int(int32(uint64(ins.Constant) & math.MaxUint32))
}
// RewriteMapOffset changes the offset of a direct load from a map.
//
// Returns an error if the instruction is not a direct load.
func (ins *Instruction) RewriteMapOffset(offset uint32) error {
if !ins.OpCode.IsDWordLoad() {
return fmt.Errorf("%s is not a 64 bit load", ins.OpCode)
}
if ins.Src != PseudoMapValue {
return errors.New("not a direct load from a map")
}
fd := uint64(ins.Constant) & math.MaxUint32
ins.Constant = int64(uint64(offset)<<32 | fd)
return nil
}
func (ins *Instruction) mapOffset() uint32 {
return uint32(uint64(ins.Constant) >> 32)
}
// IsLoadFromMap returns true if the instruction loads from a map.
//
// This covers both loading the map pointer and direct map value loads.
func (ins *Instruction) IsLoadFromMap() bool {
return ins.OpCode == LoadImmOp(DWord) && (ins.Src == PseudoMapFD || ins.Src == PseudoMapValue)
}
// IsFunctionCall returns true if the instruction calls another BPF function.
//
// This is not the same thing as a BPF helper call.
func (ins *Instruction) IsFunctionCall() bool {
return ins.OpCode.JumpOp() == Call && ins.Src == PseudoCall
}
// IsLoadOfFunctionPointer returns true if the instruction loads a function pointer.
func (ins *Instruction) IsLoadOfFunctionPointer() bool {
return ins.OpCode.IsDWordLoad() && ins.Src == PseudoFunc
}
// IsFunctionReference returns true if the instruction references another BPF
// function, either by invoking a Call jump operation or by loading a function
// pointer.
func (ins *Instruction) IsFunctionReference() bool {
return ins.IsFunctionCall() || ins.IsLoadOfFunctionPointer()
}
// IsBuiltinCall returns true if the instruction is a built-in call, i.e. BPF helper call.
func (ins *Instruction) IsBuiltinCall() bool {
return ins.OpCode.JumpOp() == Call && ins.Src == R0 && ins.Dst == R0
}
// IsConstantLoad returns true if the instruction loads a constant of the
// given size.
func (ins *Instruction) IsConstantLoad(size Size) bool {
return ins.OpCode == LoadImmOp(size) && ins.Src == R0 && ins.Offset == 0
}
// Format implements fmt.Formatter.
func (ins Instruction) Format(f fmt.State, c rune) {
if c != 'v' {
fmt.Fprintf(f, "{UNRECOGNIZED: %c}", c)
return
}
op := ins.OpCode
if op == InvalidOpCode {
fmt.Fprint(f, "INVALID")
return
}
// Omit trailing space for Exit
if op.JumpOp() == Exit {
fmt.Fprint(f, op)
return
}
if ins.IsLoadFromMap() {
fd := ins.MapPtr()
switch ins.Src {
case PseudoMapFD:
fmt.Fprintf(f, "LoadMapPtr dst: %s fd: %d", ins.Dst, fd)
case PseudoMapValue:
fmt.Fprintf(f, "LoadMapValue dst: %s, fd: %d off: %d", ins.Dst, fd, ins.mapOffset())
}
goto ref
}
fmt.Fprintf(f, "%v ", op)
switch cls := op.Class(); {
case cls.isLoadOrStore():
switch op.Mode() {
case ImmMode:
fmt.Fprintf(f, "dst: %s imm: %d", ins.Dst, ins.Constant)
case AbsMode:
fmt.Fprintf(f, "imm: %d", ins.Constant)
case IndMode:
fmt.Fprintf(f, "dst: %s src: %s imm: %d", ins.Dst, ins.Src, ins.Constant)
case MemMode:
fmt.Fprintf(f, "dst: %s src: %s off: %d imm: %d", ins.Dst, ins.Src, ins.Offset, ins.Constant)
case XAddMode:
fmt.Fprintf(f, "dst: %s src: %s", ins.Dst, ins.Src)
}
case cls.IsALU():
fmt.Fprintf(f, "dst: %s ", ins.Dst)
if op.ALUOp() == Swap || op.Source() == ImmSource {
fmt.Fprintf(f, "imm: %d", ins.Constant)
} else {
fmt.Fprintf(f, "src: %s", ins.Src)
}
case cls.IsJump():
switch jop := op.JumpOp(); jop {
case Call:
if ins.Src == PseudoCall {
// bpf-to-bpf call
fmt.Fprint(f, ins.Constant)
} else {
fmt.Fprint(f, BuiltinFunc(ins.Constant))
}
default:
fmt.Fprintf(f, "dst: %s off: %d ", ins.Dst, ins.Offset)
if op.Source() == ImmSource {
fmt.Fprintf(f, "imm: %d", ins.Constant)
} else {
fmt.Fprintf(f, "src: %s", ins.Src)
}
}
}
ref:
if ins.Reference() != "" {
fmt.Fprintf(f, " <%s>", ins.Reference())
}
}
func (ins Instruction) equal(other Instruction) bool {
return ins.OpCode == other.OpCode &&
ins.Dst == other.Dst &&
ins.Src == other.Src &&
ins.Offset == other.Offset &&
ins.Constant == other.Constant
}
// Size returns the amount of bytes ins would occupy in binary form.
func (ins Instruction) Size() uint64 {
return uint64(InstructionSize * ins.OpCode.rawInstructions())
}
// WithReference makes ins reference another Instruction by name within the same
func (ins Instruction) WithReference(ref string) Instruction {
if (ins.metadata != nil && ins.metadata.reference == ref) ||
(ins.metadata == nil && ref == "") {
return ins
}
ins.metadata = ins.metadata.copy()
ins.metadata.reference = ref
return ins
}
// Reference returns a reference (e.g. a jump) to another symbol.
func (ins Instruction) Reference() string {
if ins.metadata == nil {
return ""
}
return ins.metadata.reference
}
// metadata holds metadata about an Instruction.
type metadata struct {
// reference denotes a reference (e.g. a jump) to another symbol.
reference string
// symbol denotes an instruction at the start of a function body.
symbol string
}
// copy returns a copy of metadata.
// Always returns a valid pointer, even when called on a nil metadata.
func (m *metadata) copy() *metadata {
var copy metadata
if m != nil {
copy = *m
}
return ©
}
// Instructions is an eBPF program.
type Instructions []Instruction
// Unmarshal unmarshals an Instructions from a binary instruction stream.
// All instructions in insns are replaced by instructions decoded from r.
func (insns *Instructions) Unmarshal(r io.Reader, bo binary.ByteOrder) error {
if len(*insns) > 0 {
*insns = nil
}
var offset uint64
for {
var ins Instruction
n, err := ins.Unmarshal(r, bo)
if errors.Is(err, io.EOF) {
break
}
if err != nil {
return fmt.Errorf("offset %d: %w", offset, err)
}
*insns = append(*insns, ins)
offset += n
}
return nil
}
// Name returns the name of the function insns belongs to, if any.
func (insns Instructions) Name() string {
if len(insns) == 0 {
return ""
}
return insns[0].Symbol()
}
func (insns Instructions) String() string {
return fmt.Sprint(insns)
}
// Size returns the amount of bytes insns would occupy in binary form.
func (insns Instructions) Size() uint64 {
var sum uint64
for _, ins := range insns {
sum += ins.Size()
}
return sum
}
// RewriteMapPtr rewrites all loads of a specific map pointer to a new fd.
//
// Returns an error if the symbol isn't used, see IsUnreferencedSymbol.
func (insns Instructions) RewriteMapPtr(symbol string, fd int) error {
if symbol == "" {
return errors.New("empty symbol")
}
found := false
for i := range insns {
ins := &insns[i]
if ins.Reference() != symbol {
continue
}
if err := ins.RewriteMapPtr(fd); err != nil {
return err
}
found = true
}
if !found {
return &unreferencedSymbolError{symbol}
}
return nil
}
// SymbolOffsets returns the set of symbols and their offset in
// the instructions.
func (insns Instructions) SymbolOffsets() (map[string]int, error) {
offsets := make(map[string]int)
for i, ins := range insns {
if ins.Symbol() == "" {
continue
}
if _, ok := offsets[ins.Symbol()]; ok {
return nil, fmt.Errorf("duplicate symbol %s", ins.Symbol())
}
offsets[ins.Symbol()] = i
}
return offsets, nil
}
// FunctionReferences returns a set of symbol names these Instructions make
// bpf-to-bpf calls to.
func (insns Instructions) FunctionReferences() map[string]bool {
calls := make(map[string]bool)
for _, ins := range insns {
if ins.Constant != -1 {
// BPF-to-BPF calls have -1 constants.
continue
}
if ins.Reference() == "" {
continue
}
if !ins.IsFunctionReference() {
continue
}
calls[ins.Reference()] = true
}
return calls
}
// ReferenceOffsets returns the set of references and their offset in
// the instructions.
func (insns Instructions) ReferenceOffsets() map[string][]int {
offsets := make(map[string][]int)
for i, ins := range insns {
if ins.Reference() == "" {
continue
}
offsets[ins.Reference()] = append(offsets[ins.Reference()], i)
}
return offsets
}
// Format implements fmt.Formatter.
//
// You can control indentation of symbols by
// specifying a width. Setting a precision controls the indentation of
// instructions.
// The default character is a tab, which can be overridden by specifying
// the ' ' space flag.
func (insns Instructions) Format(f fmt.State, c rune) {
if c != 's' && c != 'v' {
fmt.Fprintf(f, "{UNKNOWN FORMAT '%c'}", c)
return
}
// Precision is better in this case, because it allows
// specifying 0 padding easily.
padding, ok := f.Precision()
if !ok {
padding = 1
}
indent := strings.Repeat("\t", padding)
if f.Flag(' ') {
indent = strings.Repeat(" ", padding)
}
symPadding, ok := f.Width()
if !ok {
symPadding = padding - 1
}
if symPadding < 0 {
symPadding = 0
}
symIndent := strings.Repeat("\t", symPadding)
if f.Flag(' ') {
symIndent = strings.Repeat(" ", symPadding)
}
// Guess how many digits we need at most, by assuming that all instructions
// are double wide.
highestOffset := len(insns) * 2
offsetWidth := int(math.Ceil(math.Log10(float64(highestOffset))))
iter := insns.Iterate()
for iter.Next() {
if iter.Ins.Symbol() != "" {
fmt.Fprintf(f, "%s%s:\n", symIndent, iter.Ins.Symbol())
}
fmt.Fprintf(f, "%s%*d: %v\n", indent, offsetWidth, iter.Offset, iter.Ins)
}
}
// Marshal encodes a BPF program into the kernel format.
//
// Returns ErrUnsatisfiedProgramReference if there is a Reference Instruction
// without a matching Symbol Instruction within insns.
func (insns Instructions) Marshal(w io.Writer, bo binary.ByteOrder) error {
if err := insns.resolveFunctionReferences(); err != nil {
return err
}
for i, ins := range insns {
if _, err := ins.Marshal(w, bo); err != nil {
return fmt.Errorf("instruction %d: %w", i, err)
}
}
return nil
}
// Tag calculates the kernel tag for a series of instructions.
//
// It mirrors bpf_prog_calc_tag in the kernel and so can be compared
// to ProgramInfo.Tag to figure out whether a loaded program matches
// certain instructions.
func (insns Instructions) Tag(bo binary.ByteOrder) (string, error) {
h := sha1.New()
for i, ins := range insns {
if ins.IsLoadFromMap() {
ins.Constant = 0
}
_, err := ins.Marshal(h, bo)
if err != nil {
return "", fmt.Errorf("instruction %d: %w", i, err)
}
}
return hex.EncodeToString(h.Sum(nil)[:unix.BPF_TAG_SIZE]), nil
}
// resolveFunctionReferences populates the Offset (or Constant, depending on
// the instruction type) field of instructions with a Reference field to point
// to the offset of the corresponding instruction with a matching Symbol field.
//
// Only Reference Instructions that are either jumps or BPF function references
// (calls or function pointer loads) are populated.
//
// Returns ErrUnsatisfiedProgramReference if there is a Reference Instruction
// without at least one corresponding Symbol Instruction within insns.
func (insns Instructions) resolveFunctionReferences() error {
// Index the offsets of instructions tagged as a symbol.
symbolOffsets := make(map[string]RawInstructionOffset)
iter := insns.Iterate()
for iter.Next() {
ins := iter.Ins
if ins.Symbol() == "" {
continue
}
if _, ok := symbolOffsets[ins.Symbol()]; ok {
return fmt.Errorf("duplicate symbol %s", ins.Symbol())
}
symbolOffsets[ins.Symbol()] = iter.Offset
}
// Find all instructions tagged as references to other symbols.
// Depending on the instruction type, populate their constant or offset
// fields to point to the symbol they refer to within the insn stream.
iter = insns.Iterate()
for iter.Next() {
i := iter.Index
offset := iter.Offset
ins := iter.Ins
if ins.Reference() == "" {
continue
}
switch {
case ins.IsFunctionReference() && ins.Constant == -1:
symOffset, ok := symbolOffsets[ins.Reference()]
if !ok {
return fmt.Errorf("%s at insn %d: symbol %q: %w", ins.OpCode, i, ins.Reference(), ErrUnsatisfiedProgramReference)
}
ins.Constant = int64(symOffset - offset - 1)
case ins.OpCode.Class().IsJump() && ins.Offset == -1:
symOffset, ok := symbolOffsets[ins.Reference()]
if !ok {
return fmt.Errorf("%s at insn %d: symbol %q: %w", ins.OpCode, i, ins.Reference(), ErrUnsatisfiedProgramReference)
}
ins.Offset = int16(symOffset - offset - 1)
}
}
return nil
}
// Iterate allows iterating a BPF program while keeping track of
// various offsets.
//
// Modifying the instruction slice will lead to undefined behaviour.
func (insns Instructions) Iterate() *InstructionIterator {
return &InstructionIterator{insns: insns}
}
// InstructionIterator iterates over a BPF program.
type InstructionIterator struct {
insns Instructions
// The instruction in question.
Ins *Instruction
// The index of the instruction in the original instruction slice.
Index int
// The offset of the instruction in raw BPF instructions. This accounts
// for double-wide instructions.
Offset RawInstructionOffset
}
// Next returns true as long as there are any instructions remaining.
func (iter *InstructionIterator) Next() bool {
if len(iter.insns) == 0 {
return false
}
if iter.Ins != nil {
iter.Index++
iter.Offset += RawInstructionOffset(iter.Ins.OpCode.rawInstructions())
}
iter.Ins = &iter.insns[0]
iter.insns = iter.insns[1:]
return true
}
type bpfRegisters uint8
func newBPFRegisters(dst, src Register, bo binary.ByteOrder) (bpfRegisters, error) {
switch bo {
case binary.LittleEndian:
return bpfRegisters((src << 4) | (dst & 0xF)), nil
case binary.BigEndian:
return bpfRegisters((dst << 4) | (src & 0xF)), nil
default:
return 0, fmt.Errorf("unrecognized ByteOrder %T", bo)
}
}
type unreferencedSymbolError struct {
symbol string
}
func (use *unreferencedSymbolError) Error() string {
return fmt.Sprintf("unreferenced symbol %s", use.symbol)
}
// IsUnreferencedSymbol returns true if err was caused by
// an unreferenced symbol.
func IsUnreferencedSymbol(err error) bool {
_, ok := err.(*unreferencedSymbolError)
return ok
}