569 lines
17 KiB
Go
569 lines
17 KiB
Go
package link
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import (
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"bytes"
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"crypto/rand"
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"errors"
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"fmt"
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"os"
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"path/filepath"
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"runtime"
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"strings"
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"sync"
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"syscall"
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"unsafe"
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"github.com/cilium/ebpf"
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"github.com/cilium/ebpf/internal/sys"
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"github.com/cilium/ebpf/internal/unix"
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)
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var (
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kprobeEventsPath = filepath.Join(tracefsPath, "kprobe_events")
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kprobeRetprobeBit = struct {
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once sync.Once
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value uint64
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err error
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}{}
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)
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type probeType uint8
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type probeArgs struct {
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symbol, group, path string
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offset, refCtrOffset, cookie uint64
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pid int
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ret bool
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}
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// KprobeOptions defines additional parameters that will be used
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// when loading Kprobes.
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type KprobeOptions struct {
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// Arbitrary value that can be fetched from an eBPF program
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// via `bpf_get_attach_cookie()`.
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//
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// Needs kernel 5.15+.
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Cookie uint64
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// Offset of the kprobe relative to the traced symbol.
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// Can be used to insert kprobes at arbitrary offsets in kernel functions,
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// e.g. in places where functions have been inlined.
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Offset uint64
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}
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const (
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kprobeType probeType = iota
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uprobeType
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)
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func (pt probeType) String() string {
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if pt == kprobeType {
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return "kprobe"
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}
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return "uprobe"
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}
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func (pt probeType) EventsPath() string {
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if pt == kprobeType {
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return kprobeEventsPath
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}
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return uprobeEventsPath
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}
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func (pt probeType) PerfEventType(ret bool) perfEventType {
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if pt == kprobeType {
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if ret {
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return kretprobeEvent
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}
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return kprobeEvent
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}
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if ret {
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return uretprobeEvent
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}
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return uprobeEvent
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}
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func (pt probeType) RetprobeBit() (uint64, error) {
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if pt == kprobeType {
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return kretprobeBit()
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}
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return uretprobeBit()
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}
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// Kprobe attaches the given eBPF program to a perf event that fires when the
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// given kernel symbol starts executing. See /proc/kallsyms for available
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// symbols. For example, printk():
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//
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// kp, err := Kprobe("printk", prog, nil)
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//
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// Losing the reference to the resulting Link (kp) will close the Kprobe
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// and prevent further execution of prog. The Link must be Closed during
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// program shutdown to avoid leaking system resources.
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func Kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error) {
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k, err := kprobe(symbol, prog, opts, false)
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if err != nil {
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return nil, err
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}
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lnk, err := attachPerfEvent(k, prog)
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if err != nil {
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k.Close()
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return nil, err
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}
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return lnk, nil
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}
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// Kretprobe attaches the given eBPF program to a perf event that fires right
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// before the given kernel symbol exits, with the function stack left intact.
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// See /proc/kallsyms for available symbols. For example, printk():
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//
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// kp, err := Kretprobe("printk", prog, nil)
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//
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// Losing the reference to the resulting Link (kp) will close the Kretprobe
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// and prevent further execution of prog. The Link must be Closed during
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// program shutdown to avoid leaking system resources.
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func Kretprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error) {
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k, err := kprobe(symbol, prog, opts, true)
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if err != nil {
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return nil, err
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}
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lnk, err := attachPerfEvent(k, prog)
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if err != nil {
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k.Close()
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return nil, err
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}
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return lnk, nil
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}
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// isValidKprobeSymbol implements the equivalent of a regex match
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// against "^[a-zA-Z_][0-9a-zA-Z_.]*$".
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func isValidKprobeSymbol(s string) bool {
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if len(s) < 1 {
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return false
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}
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for i, c := range []byte(s) {
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switch {
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case c >= 'a' && c <= 'z':
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case c >= 'A' && c <= 'Z':
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case c == '_':
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case i > 0 && c >= '0' && c <= '9':
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// Allow `.` in symbol name. GCC-compiled kernel may change symbol name
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// to have a `.isra.$n` suffix, like `udp_send_skb.isra.52`.
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// See: https://gcc.gnu.org/gcc-10/changes.html
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case i > 0 && c == '.':
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default:
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return false
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}
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}
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return true
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}
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// kprobe opens a perf event on the given symbol and attaches prog to it.
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// If ret is true, create a kretprobe.
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func kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions, ret bool) (*perfEvent, error) {
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if symbol == "" {
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return nil, fmt.Errorf("symbol name cannot be empty: %w", errInvalidInput)
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}
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if prog == nil {
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return nil, fmt.Errorf("prog cannot be nil: %w", errInvalidInput)
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}
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if !isValidKprobeSymbol(symbol) {
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return nil, fmt.Errorf("symbol '%s' must be a valid symbol in /proc/kallsyms: %w", symbol, errInvalidInput)
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}
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if prog.Type() != ebpf.Kprobe {
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return nil, fmt.Errorf("eBPF program type %s is not a Kprobe: %w", prog.Type(), errInvalidInput)
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}
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args := probeArgs{
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pid: perfAllThreads,
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symbol: symbol,
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ret: ret,
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}
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if opts != nil {
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args.cookie = opts.Cookie
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args.offset = opts.Offset
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}
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// Use kprobe PMU if the kernel has it available.
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tp, err := pmuKprobe(args)
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if errors.Is(err, os.ErrNotExist) {
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args.symbol = platformPrefix(symbol)
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tp, err = pmuKprobe(args)
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}
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if err == nil {
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return tp, nil
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}
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if err != nil && !errors.Is(err, ErrNotSupported) {
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return nil, fmt.Errorf("creating perf_kprobe PMU: %w", err)
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}
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// Use tracefs if kprobe PMU is missing.
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args.symbol = symbol
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tp, err = tracefsKprobe(args)
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if errors.Is(err, os.ErrNotExist) {
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args.symbol = platformPrefix(symbol)
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tp, err = tracefsKprobe(args)
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}
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if err != nil {
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return nil, fmt.Errorf("creating trace event '%s' in tracefs: %w", symbol, err)
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}
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return tp, nil
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}
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// pmuKprobe opens a perf event based on the kprobe PMU.
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// Returns os.ErrNotExist if the given symbol does not exist in the kernel.
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func pmuKprobe(args probeArgs) (*perfEvent, error) {
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return pmuProbe(kprobeType, args)
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}
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// pmuProbe opens a perf event based on a Performance Monitoring Unit.
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//
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// Requires at least a 4.17 kernel.
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// e12f03d7031a "perf/core: Implement the 'perf_kprobe' PMU"
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// 33ea4b24277b "perf/core: Implement the 'perf_uprobe' PMU"
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//
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// Returns ErrNotSupported if the kernel doesn't support perf_[k,u]probe PMU
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func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
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// Getting the PMU type will fail if the kernel doesn't support
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// the perf_[k,u]probe PMU.
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et, err := getPMUEventType(typ)
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if err != nil {
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return nil, err
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}
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var config uint64
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if args.ret {
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bit, err := typ.RetprobeBit()
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if err != nil {
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return nil, err
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}
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config |= 1 << bit
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}
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var (
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attr unix.PerfEventAttr
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sp unsafe.Pointer
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)
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switch typ {
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case kprobeType:
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// Create a pointer to a NUL-terminated string for the kernel.
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sp, err = unsafeStringPtr(args.symbol)
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if err != nil {
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return nil, err
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}
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attr = unix.PerfEventAttr{
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// The minimum size required for PMU kprobes is PERF_ATTR_SIZE_VER1,
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// since it added the config2 (Ext2) field. Use Ext2 as probe_offset.
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Size: unix.PERF_ATTR_SIZE_VER1,
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Type: uint32(et), // PMU event type read from sysfs
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Ext1: uint64(uintptr(sp)), // Kernel symbol to trace
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Ext2: args.offset, // Kernel symbol offset
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Config: config, // Retprobe flag
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}
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case uprobeType:
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sp, err = unsafeStringPtr(args.path)
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if err != nil {
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return nil, err
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}
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if args.refCtrOffset != 0 {
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config |= args.refCtrOffset << uprobeRefCtrOffsetShift
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}
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attr = unix.PerfEventAttr{
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// The minimum size required for PMU uprobes is PERF_ATTR_SIZE_VER1,
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// since it added the config2 (Ext2) field. The Size field controls the
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// size of the internal buffer the kernel allocates for reading the
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// perf_event_attr argument from userspace.
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Size: unix.PERF_ATTR_SIZE_VER1,
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Type: uint32(et), // PMU event type read from sysfs
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Ext1: uint64(uintptr(sp)), // Uprobe path
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Ext2: args.offset, // Uprobe offset
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Config: config, // RefCtrOffset, Retprobe flag
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}
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}
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rawFd, err := unix.PerfEventOpen(&attr, args.pid, 0, -1, unix.PERF_FLAG_FD_CLOEXEC)
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// On some old kernels, kprobe PMU doesn't allow `.` in symbol names and
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// return -EINVAL. Return ErrNotSupported to allow falling back to tracefs.
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// https://github.com/torvalds/linux/blob/94710cac0ef4/kernel/trace/trace_kprobe.c#L340-L343
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if errors.Is(err, unix.EINVAL) && strings.Contains(args.symbol, ".") {
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return nil, fmt.Errorf("symbol '%s+%#x': older kernels don't accept dots: %w", args.symbol, args.offset, ErrNotSupported)
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}
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// Since commit 97c753e62e6c, ENOENT is correctly returned instead of EINVAL
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// when trying to create a kretprobe for a missing symbol. Make sure ENOENT
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// is returned to the caller.
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if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
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return nil, fmt.Errorf("symbol '%s+%#x' not found: %w", args.symbol, args.offset, os.ErrNotExist)
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}
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// Since commit ab105a4fb894, -EILSEQ is returned when a kprobe sym+offset is resolved
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// to an invalid insn boundary.
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if errors.Is(err, syscall.EILSEQ) {
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return nil, fmt.Errorf("symbol '%s+%#x' not found (bad insn boundary): %w", args.symbol, args.offset, os.ErrNotExist)
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}
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// Since at least commit cb9a19fe4aa51, ENOTSUPP is returned
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// when attempting to set a uprobe on a trap instruction.
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if errors.Is(err, unix.ENOTSUPP) {
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return nil, fmt.Errorf("failed setting uprobe on offset %#x (possible trap insn): %w", args.offset, err)
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}
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if err != nil {
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return nil, fmt.Errorf("opening perf event: %w", err)
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}
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// Ensure the string pointer is not collected before PerfEventOpen returns.
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runtime.KeepAlive(sp)
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fd, err := sys.NewFD(rawFd)
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if err != nil {
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return nil, err
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}
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// Kernel has perf_[k,u]probe PMU available, initialize perf event.
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return &perfEvent{
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typ: typ.PerfEventType(args.ret),
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name: args.symbol,
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pmuID: et,
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cookie: args.cookie,
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fd: fd,
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}, nil
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}
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// tracefsKprobe creates a Kprobe tracefs entry.
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func tracefsKprobe(args probeArgs) (*perfEvent, error) {
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return tracefsProbe(kprobeType, args)
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}
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// tracefsProbe creates a trace event by writing an entry to <tracefs>/[k,u]probe_events.
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// A new trace event group name is generated on every call to support creating
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// multiple trace events for the same kernel or userspace symbol.
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// Path and offset are only set in the case of uprobe(s) and are used to set
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// the executable/library path on the filesystem and the offset where the probe is inserted.
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// A perf event is then opened on the newly-created trace event and returned to the caller.
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func tracefsProbe(typ probeType, args probeArgs) (_ *perfEvent, err error) {
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// Generate a random string for each trace event we attempt to create.
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// This value is used as the 'group' token in tracefs to allow creating
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// multiple kprobe trace events with the same name.
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group, err := randomGroup("ebpf")
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if err != nil {
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return nil, fmt.Errorf("randomizing group name: %w", err)
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}
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args.group = group
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// Before attempting to create a trace event through tracefs,
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// check if an event with the same group and name already exists.
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// Kernels 4.x and earlier don't return os.ErrExist on writing a duplicate
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// entry, so we need to rely on reads for detecting uniqueness.
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_, err = getTraceEventID(group, args.symbol)
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if err == nil {
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return nil, fmt.Errorf("trace event already exists: %s/%s", group, args.symbol)
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}
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if err != nil && !errors.Is(err, os.ErrNotExist) {
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return nil, fmt.Errorf("checking trace event %s/%s: %w", group, args.symbol, err)
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}
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// Create the [k,u]probe trace event using tracefs.
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if err := createTraceFSProbeEvent(typ, args); err != nil {
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return nil, fmt.Errorf("creating probe entry on tracefs: %w", err)
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}
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defer func() {
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if err != nil {
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// Make sure we clean up the created tracefs event when we return error.
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// If a livepatch handler is already active on the symbol, the write to
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// tracefs will succeed, a trace event will show up, but creating the
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// perf event will fail with EBUSY.
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_ = closeTraceFSProbeEvent(typ, args.group, args.symbol)
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}
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}()
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// Get the newly-created trace event's id.
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tid, err := getTraceEventID(group, args.symbol)
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if err != nil {
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return nil, fmt.Errorf("getting trace event id: %w", err)
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}
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|
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// Kprobes are ephemeral tracepoints and share the same perf event type.
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fd, err := openTracepointPerfEvent(tid, args.pid)
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if err != nil {
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return nil, err
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}
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return &perfEvent{
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typ: typ.PerfEventType(args.ret),
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group: group,
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name: args.symbol,
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tracefsID: tid,
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cookie: args.cookie,
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fd: fd,
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}, nil
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}
|
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|
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// createTraceFSProbeEvent creates a new ephemeral trace event by writing to
|
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// <tracefs>/[k,u]probe_events. Returns os.ErrNotExist if symbol is not a valid
|
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// kernel symbol, or if it is not traceable with kprobes. Returns os.ErrExist
|
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// if a probe with the same group and symbol already exists.
|
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func createTraceFSProbeEvent(typ probeType, args probeArgs) error {
|
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// Open the kprobe_events file in tracefs.
|
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f, err := os.OpenFile(typ.EventsPath(), os.O_APPEND|os.O_WRONLY, 0666)
|
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if err != nil {
|
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return fmt.Errorf("error opening '%s': %w", typ.EventsPath(), err)
|
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}
|
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defer f.Close()
|
|
|
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var pe, token string
|
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switch typ {
|
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case kprobeType:
|
|
// The kprobe_events syntax is as follows (see Documentation/trace/kprobetrace.txt):
|
|
// p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
|
|
// r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
|
|
// -:[GRP/]EVENT : Clear a probe
|
|
//
|
|
// Some examples:
|
|
// r:ebpf_1234/r_my_kretprobe nf_conntrack_destroy
|
|
// p:ebpf_5678/p_my_kprobe __x64_sys_execve
|
|
//
|
|
// Leaving the kretprobe's MAXACTIVE set to 0 (or absent) will make the
|
|
// kernel default to NR_CPUS. This is desired in most eBPF cases since
|
|
// subsampling or rate limiting logic can be more accurately implemented in
|
|
// the eBPF program itself.
|
|
// See Documentation/kprobes.txt for more details.
|
|
token = kprobeToken(args)
|
|
pe = fmt.Sprintf("%s:%s/%s %s", probePrefix(args.ret), args.group, sanitizeSymbol(args.symbol), token)
|
|
case uprobeType:
|
|
// The uprobe_events syntax is as follows:
|
|
// p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a probe
|
|
// r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return probe
|
|
// -:[GRP/]EVENT : Clear a probe
|
|
//
|
|
// Some examples:
|
|
// r:ebpf_1234/readline /bin/bash:0x12345
|
|
// p:ebpf_5678/main_mySymbol /bin/mybin:0x12345(0x123)
|
|
//
|
|
// See Documentation/trace/uprobetracer.txt for more details.
|
|
token = uprobeToken(args)
|
|
pe = fmt.Sprintf("%s:%s/%s %s", probePrefix(args.ret), args.group, args.symbol, token)
|
|
}
|
|
_, err = f.WriteString(pe)
|
|
// Since commit 97c753e62e6c, ENOENT is correctly returned instead of EINVAL
|
|
// when trying to create a kretprobe for a missing symbol. Make sure ENOENT
|
|
// is returned to the caller.
|
|
// EINVAL is also returned on pre-5.2 kernels when the `SYM[+offs]` token
|
|
// is resolved to an invalid insn boundary.
|
|
if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
|
|
return fmt.Errorf("token %s: %w", token, os.ErrNotExist)
|
|
}
|
|
// Since commit ab105a4fb894, -EILSEQ is returned when a kprobe sym+offset is resolved
|
|
// to an invalid insn boundary.
|
|
if errors.Is(err, syscall.EILSEQ) {
|
|
return fmt.Errorf("token %s: bad insn boundary: %w", token, os.ErrNotExist)
|
|
}
|
|
// ERANGE is returned when the `SYM[+offs]` token is too big and cannot
|
|
// be resolved.
|
|
if errors.Is(err, syscall.ERANGE) {
|
|
return fmt.Errorf("token %s: offset too big: %w", token, os.ErrNotExist)
|
|
}
|
|
if err != nil {
|
|
return fmt.Errorf("writing '%s' to '%s': %w", pe, typ.EventsPath(), err)
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// closeTraceFSProbeEvent removes the [k,u]probe with the given type, group and symbol
|
|
// from <tracefs>/[k,u]probe_events.
|
|
func closeTraceFSProbeEvent(typ probeType, group, symbol string) error {
|
|
f, err := os.OpenFile(typ.EventsPath(), os.O_APPEND|os.O_WRONLY, 0666)
|
|
if err != nil {
|
|
return fmt.Errorf("error opening %s: %w", typ.EventsPath(), err)
|
|
}
|
|
defer f.Close()
|
|
|
|
// See [k,u]probe_events syntax above. The probe type does not need to be specified
|
|
// for removals.
|
|
pe := fmt.Sprintf("-:%s/%s", group, sanitizeSymbol(symbol))
|
|
if _, err = f.WriteString(pe); err != nil {
|
|
return fmt.Errorf("writing '%s' to '%s': %w", pe, typ.EventsPath(), err)
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// randomGroup generates a pseudorandom string for use as a tracefs group name.
|
|
// Returns an error when the output string would exceed 63 characters (kernel
|
|
// limitation), when rand.Read() fails or when prefix contains characters not
|
|
// allowed by isValidTraceID.
|
|
func randomGroup(prefix string) (string, error) {
|
|
if !isValidTraceID(prefix) {
|
|
return "", fmt.Errorf("prefix '%s' must be alphanumeric or underscore: %w", prefix, errInvalidInput)
|
|
}
|
|
|
|
b := make([]byte, 8)
|
|
if _, err := rand.Read(b); err != nil {
|
|
return "", fmt.Errorf("reading random bytes: %w", err)
|
|
}
|
|
|
|
group := fmt.Sprintf("%s_%x", prefix, b)
|
|
if len(group) > 63 {
|
|
return "", fmt.Errorf("group name '%s' cannot be longer than 63 characters: %w", group, errInvalidInput)
|
|
}
|
|
|
|
return group, nil
|
|
}
|
|
|
|
func probePrefix(ret bool) string {
|
|
if ret {
|
|
return "r"
|
|
}
|
|
return "p"
|
|
}
|
|
|
|
// determineRetprobeBit reads a Performance Monitoring Unit's retprobe bit
|
|
// from /sys/bus/event_source/devices/<pmu>/format/retprobe.
|
|
func determineRetprobeBit(typ probeType) (uint64, error) {
|
|
p := filepath.Join("/sys/bus/event_source/devices/", typ.String(), "/format/retprobe")
|
|
|
|
data, err := os.ReadFile(p)
|
|
if err != nil {
|
|
return 0, err
|
|
}
|
|
|
|
var rp uint64
|
|
n, err := fmt.Sscanf(string(bytes.TrimSpace(data)), "config:%d", &rp)
|
|
if err != nil {
|
|
return 0, fmt.Errorf("parse retprobe bit: %w", err)
|
|
}
|
|
if n != 1 {
|
|
return 0, fmt.Errorf("parse retprobe bit: expected 1 item, got %d", n)
|
|
}
|
|
|
|
return rp, nil
|
|
}
|
|
|
|
func kretprobeBit() (uint64, error) {
|
|
kprobeRetprobeBit.once.Do(func() {
|
|
kprobeRetprobeBit.value, kprobeRetprobeBit.err = determineRetprobeBit(kprobeType)
|
|
})
|
|
return kprobeRetprobeBit.value, kprobeRetprobeBit.err
|
|
}
|
|
|
|
// kprobeToken creates the SYM[+offs] token for the tracefs api.
|
|
func kprobeToken(args probeArgs) string {
|
|
po := args.symbol
|
|
|
|
if args.offset != 0 {
|
|
po += fmt.Sprintf("+%#x", args.offset)
|
|
}
|
|
|
|
return po
|
|
}
|