mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-05 01:52:46 +00:00
395 lines
12 KiB
Go
395 lines
12 KiB
Go
|
package link
|
||
|
|
||
|
import (
|
||
|
"bytes"
|
||
|
"errors"
|
||
|
"fmt"
|
||
|
"os"
|
||
|
"path/filepath"
|
||
|
"runtime"
|
||
|
"strconv"
|
||
|
"strings"
|
||
|
"unsafe"
|
||
|
|
||
|
"github.com/cilium/ebpf"
|
||
|
"github.com/cilium/ebpf/asm"
|
||
|
"github.com/cilium/ebpf/internal"
|
||
|
"github.com/cilium/ebpf/internal/sys"
|
||
|
"github.com/cilium/ebpf/internal/unix"
|
||
|
)
|
||
|
|
||
|
// Getting the terminology right is usually the hardest part. For posterity and
|
||
|
// for staying sane during implementation:
|
||
|
//
|
||
|
// - trace event: Representation of a kernel runtime hook. Filesystem entries
|
||
|
// under <tracefs>/events. Can be tracepoints (static), kprobes or uprobes.
|
||
|
// Can be instantiated into perf events (see below).
|
||
|
// - tracepoint: A predetermined hook point in the kernel. Exposed as trace
|
||
|
// events in (sub)directories under <tracefs>/events. Cannot be closed or
|
||
|
// removed, they are static.
|
||
|
// - k(ret)probe: Ephemeral trace events based on entry or exit points of
|
||
|
// exported kernel symbols. kprobe-based (tracefs) trace events can be
|
||
|
// created system-wide by writing to the <tracefs>/kprobe_events file, or
|
||
|
// they can be scoped to the current process by creating PMU perf events.
|
||
|
// - u(ret)probe: Ephemeral trace events based on user provides ELF binaries
|
||
|
// and offsets. uprobe-based (tracefs) trace events can be
|
||
|
// created system-wide by writing to the <tracefs>/uprobe_events file, or
|
||
|
// they can be scoped to the current process by creating PMU perf events.
|
||
|
// - perf event: An object instantiated based on an existing trace event or
|
||
|
// kernel symbol. Referred to by fd in userspace.
|
||
|
// Exactly one eBPF program can be attached to a perf event. Multiple perf
|
||
|
// events can be created from a single trace event. Closing a perf event
|
||
|
// stops any further invocations of the attached eBPF program.
|
||
|
|
||
|
var (
|
||
|
tracefsPath = "/sys/kernel/debug/tracing"
|
||
|
|
||
|
errInvalidInput = errors.New("invalid input")
|
||
|
)
|
||
|
|
||
|
const (
|
||
|
perfAllThreads = -1
|
||
|
)
|
||
|
|
||
|
type perfEventType uint8
|
||
|
|
||
|
const (
|
||
|
tracepointEvent perfEventType = iota
|
||
|
kprobeEvent
|
||
|
kretprobeEvent
|
||
|
uprobeEvent
|
||
|
uretprobeEvent
|
||
|
)
|
||
|
|
||
|
// A perfEvent represents a perf event kernel object. Exactly one eBPF program
|
||
|
// can be attached to it. It is created based on a tracefs trace event or a
|
||
|
// Performance Monitoring Unit (PMU).
|
||
|
type perfEvent struct {
|
||
|
// The event type determines the types of programs that can be attached.
|
||
|
typ perfEventType
|
||
|
|
||
|
// Group and name of the tracepoint/kprobe/uprobe.
|
||
|
group string
|
||
|
name string
|
||
|
|
||
|
// PMU event ID read from sysfs. Valid IDs are non-zero.
|
||
|
pmuID uint64
|
||
|
// ID of the trace event read from tracefs. Valid IDs are non-zero.
|
||
|
tracefsID uint64
|
||
|
|
||
|
// User provided arbitrary value.
|
||
|
cookie uint64
|
||
|
|
||
|
// This is the perf event FD.
|
||
|
fd *sys.FD
|
||
|
}
|
||
|
|
||
|
func (pe *perfEvent) Close() error {
|
||
|
if err := pe.fd.Close(); err != nil {
|
||
|
return fmt.Errorf("closing perf event fd: %w", err)
|
||
|
}
|
||
|
|
||
|
switch pe.typ {
|
||
|
case kprobeEvent, kretprobeEvent:
|
||
|
// Clean up kprobe tracefs entry.
|
||
|
if pe.tracefsID != 0 {
|
||
|
return closeTraceFSProbeEvent(kprobeType, pe.group, pe.name)
|
||
|
}
|
||
|
case uprobeEvent, uretprobeEvent:
|
||
|
// Clean up uprobe tracefs entry.
|
||
|
if pe.tracefsID != 0 {
|
||
|
return closeTraceFSProbeEvent(uprobeType, pe.group, pe.name)
|
||
|
}
|
||
|
case tracepointEvent:
|
||
|
// Tracepoint trace events don't hold any extra resources.
|
||
|
return nil
|
||
|
}
|
||
|
|
||
|
return nil
|
||
|
}
|
||
|
|
||
|
// perfEventLink represents a bpf perf link.
|
||
|
type perfEventLink struct {
|
||
|
RawLink
|
||
|
pe *perfEvent
|
||
|
}
|
||
|
|
||
|
func (pl *perfEventLink) isLink() {}
|
||
|
|
||
|
// Pinning requires the underlying perf event FD to stay open.
|
||
|
//
|
||
|
// | PerfEvent FD | BpfLink FD | Works |
|
||
|
// |--------------|------------|-------|
|
||
|
// | Open | Open | Yes |
|
||
|
// | Closed | Open | No |
|
||
|
// | Open | Closed | No (Pin() -> EINVAL) |
|
||
|
// | Closed | Closed | No (Pin() -> EINVAL) |
|
||
|
//
|
||
|
// There is currently no pretty way to recover the perf event FD
|
||
|
// when loading a pinned link, so leave as not supported for now.
|
||
|
func (pl *perfEventLink) Pin(string) error {
|
||
|
return fmt.Errorf("perf event link pin: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
func (pl *perfEventLink) Unpin() error {
|
||
|
return fmt.Errorf("perf event link unpin: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
func (pl *perfEventLink) Close() error {
|
||
|
if err := pl.pe.Close(); err != nil {
|
||
|
return fmt.Errorf("perf event link close: %w", err)
|
||
|
}
|
||
|
return pl.fd.Close()
|
||
|
}
|
||
|
|
||
|
func (pl *perfEventLink) Update(prog *ebpf.Program) error {
|
||
|
return fmt.Errorf("perf event link update: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
// perfEventIoctl implements Link and handles the perf event lifecycle
|
||
|
// via ioctl().
|
||
|
type perfEventIoctl struct {
|
||
|
*perfEvent
|
||
|
}
|
||
|
|
||
|
func (pi *perfEventIoctl) isLink() {}
|
||
|
|
||
|
// Since 4.15 (e87c6bc3852b "bpf: permit multiple bpf attachments for a single perf event"),
|
||
|
// calling PERF_EVENT_IOC_SET_BPF appends the given program to a prog_array
|
||
|
// owned by the perf event, which means multiple programs can be attached
|
||
|
// simultaneously.
|
||
|
//
|
||
|
// Before 4.15, calling PERF_EVENT_IOC_SET_BPF more than once on a perf event
|
||
|
// returns EEXIST.
|
||
|
//
|
||
|
// Detaching a program from a perf event is currently not possible, so a
|
||
|
// program replacement mechanism cannot be implemented for perf events.
|
||
|
func (pi *perfEventIoctl) Update(prog *ebpf.Program) error {
|
||
|
return fmt.Errorf("perf event ioctl update: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
func (pi *perfEventIoctl) Pin(string) error {
|
||
|
return fmt.Errorf("perf event ioctl pin: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
func (pi *perfEventIoctl) Unpin() error {
|
||
|
return fmt.Errorf("perf event ioctl unpin: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
func (pi *perfEventIoctl) Info() (*Info, error) {
|
||
|
return nil, fmt.Errorf("perf event ioctl info: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
// attach the given eBPF prog to the perf event stored in pe.
|
||
|
// pe must contain a valid perf event fd.
|
||
|
// prog's type must match the program type stored in pe.
|
||
|
func attachPerfEvent(pe *perfEvent, prog *ebpf.Program) (Link, error) {
|
||
|
if prog == nil {
|
||
|
return nil, errors.New("cannot attach a nil program")
|
||
|
}
|
||
|
if prog.FD() < 0 {
|
||
|
return nil, fmt.Errorf("invalid program: %w", sys.ErrClosedFd)
|
||
|
}
|
||
|
|
||
|
switch pe.typ {
|
||
|
case kprobeEvent, kretprobeEvent, uprobeEvent, uretprobeEvent:
|
||
|
if t := prog.Type(); t != ebpf.Kprobe {
|
||
|
return nil, fmt.Errorf("invalid program type (expected %s): %s", ebpf.Kprobe, t)
|
||
|
}
|
||
|
case tracepointEvent:
|
||
|
if t := prog.Type(); t != ebpf.TracePoint {
|
||
|
return nil, fmt.Errorf("invalid program type (expected %s): %s", ebpf.TracePoint, t)
|
||
|
}
|
||
|
default:
|
||
|
return nil, fmt.Errorf("unknown perf event type: %d", pe.typ)
|
||
|
}
|
||
|
|
||
|
if err := haveBPFLinkPerfEvent(); err == nil {
|
||
|
return attachPerfEventLink(pe, prog)
|
||
|
}
|
||
|
return attachPerfEventIoctl(pe, prog)
|
||
|
}
|
||
|
|
||
|
func attachPerfEventIoctl(pe *perfEvent, prog *ebpf.Program) (*perfEventIoctl, error) {
|
||
|
if pe.cookie != 0 {
|
||
|
return nil, fmt.Errorf("cookies are not supported: %w", ErrNotSupported)
|
||
|
}
|
||
|
|
||
|
// Assign the eBPF program to the perf event.
|
||
|
err := unix.IoctlSetInt(pe.fd.Int(), unix.PERF_EVENT_IOC_SET_BPF, prog.FD())
|
||
|
if err != nil {
|
||
|
return nil, fmt.Errorf("setting perf event bpf program: %w", err)
|
||
|
}
|
||
|
|
||
|
// PERF_EVENT_IOC_ENABLE and _DISABLE ignore their given values.
|
||
|
if err := unix.IoctlSetInt(pe.fd.Int(), unix.PERF_EVENT_IOC_ENABLE, 0); err != nil {
|
||
|
return nil, fmt.Errorf("enable perf event: %s", err)
|
||
|
}
|
||
|
|
||
|
pi := &perfEventIoctl{pe}
|
||
|
|
||
|
// Close the perf event when its reference is lost to avoid leaking system resources.
|
||
|
runtime.SetFinalizer(pi, (*perfEventIoctl).Close)
|
||
|
return pi, nil
|
||
|
}
|
||
|
|
||
|
// Use the bpf api to attach the perf event (BPF_LINK_TYPE_PERF_EVENT, 5.15+).
|
||
|
//
|
||
|
// https://github.com/torvalds/linux/commit/b89fbfbb854c9afc3047e8273cc3a694650b802e
|
||
|
func attachPerfEventLink(pe *perfEvent, prog *ebpf.Program) (*perfEventLink, error) {
|
||
|
fd, err := sys.LinkCreatePerfEvent(&sys.LinkCreatePerfEventAttr{
|
||
|
ProgFd: uint32(prog.FD()),
|
||
|
TargetFd: pe.fd.Uint(),
|
||
|
AttachType: sys.BPF_PERF_EVENT,
|
||
|
BpfCookie: pe.cookie,
|
||
|
})
|
||
|
if err != nil {
|
||
|
return nil, fmt.Errorf("cannot create bpf perf link: %v", err)
|
||
|
}
|
||
|
|
||
|
pl := &perfEventLink{RawLink{fd: fd}, pe}
|
||
|
|
||
|
// Close the perf event when its reference is lost to avoid leaking system resources.
|
||
|
runtime.SetFinalizer(pl, (*perfEventLink).Close)
|
||
|
return pl, nil
|
||
|
}
|
||
|
|
||
|
// unsafeStringPtr returns an unsafe.Pointer to a NUL-terminated copy of str.
|
||
|
func unsafeStringPtr(str string) (unsafe.Pointer, error) {
|
||
|
p, err := unix.BytePtrFromString(str)
|
||
|
if err != nil {
|
||
|
return nil, err
|
||
|
}
|
||
|
return unsafe.Pointer(p), nil
|
||
|
}
|
||
|
|
||
|
// getTraceEventID reads a trace event's ID from tracefs given its group and name.
|
||
|
// The kernel requires group and name to be alphanumeric or underscore.
|
||
|
//
|
||
|
// name automatically has its invalid symbols converted to underscores so the caller
|
||
|
// can pass a raw symbol name, e.g. a kernel symbol containing dots.
|
||
|
func getTraceEventID(group, name string) (uint64, error) {
|
||
|
name = sanitizeSymbol(name)
|
||
|
tid, err := uint64FromFile(tracefsPath, "events", group, name, "id")
|
||
|
if errors.Is(err, os.ErrNotExist) {
|
||
|
return 0, fmt.Errorf("trace event %s/%s: %w", group, name, os.ErrNotExist)
|
||
|
}
|
||
|
if err != nil {
|
||
|
return 0, fmt.Errorf("reading trace event ID of %s/%s: %w", group, name, err)
|
||
|
}
|
||
|
|
||
|
return tid, nil
|
||
|
}
|
||
|
|
||
|
// getPMUEventType reads a Performance Monitoring Unit's type (numeric identifier)
|
||
|
// from /sys/bus/event_source/devices/<pmu>/type.
|
||
|
//
|
||
|
// Returns ErrNotSupported if the pmu type is not supported.
|
||
|
func getPMUEventType(typ probeType) (uint64, error) {
|
||
|
et, err := uint64FromFile("/sys/bus/event_source/devices", typ.String(), "type")
|
||
|
if errors.Is(err, os.ErrNotExist) {
|
||
|
return 0, fmt.Errorf("pmu type %s: %w", typ, ErrNotSupported)
|
||
|
}
|
||
|
if err != nil {
|
||
|
return 0, fmt.Errorf("reading pmu type %s: %w", typ, err)
|
||
|
}
|
||
|
|
||
|
return et, nil
|
||
|
}
|
||
|
|
||
|
// openTracepointPerfEvent opens a tracepoint-type perf event. System-wide
|
||
|
// [k,u]probes created by writing to <tracefs>/[k,u]probe_events are tracepoints
|
||
|
// behind the scenes, and can be attached to using these perf events.
|
||
|
func openTracepointPerfEvent(tid uint64, pid int) (*sys.FD, error) {
|
||
|
attr := unix.PerfEventAttr{
|
||
|
Type: unix.PERF_TYPE_TRACEPOINT,
|
||
|
Config: tid,
|
||
|
Sample_type: unix.PERF_SAMPLE_RAW,
|
||
|
Sample: 1,
|
||
|
Wakeup: 1,
|
||
|
}
|
||
|
|
||
|
fd, err := unix.PerfEventOpen(&attr, pid, 0, -1, unix.PERF_FLAG_FD_CLOEXEC)
|
||
|
if err != nil {
|
||
|
return nil, fmt.Errorf("opening tracepoint perf event: %w", err)
|
||
|
}
|
||
|
|
||
|
return sys.NewFD(fd)
|
||
|
}
|
||
|
|
||
|
// uint64FromFile reads a uint64 from a file. All elements of path are sanitized
|
||
|
// and joined onto base. Returns error if base no longer prefixes the path after
|
||
|
// joining all components.
|
||
|
func uint64FromFile(base string, path ...string) (uint64, error) {
|
||
|
l := filepath.Join(path...)
|
||
|
p := filepath.Join(base, l)
|
||
|
if !strings.HasPrefix(p, base) {
|
||
|
return 0, fmt.Errorf("path '%s' attempts to escape base path '%s': %w", l, base, errInvalidInput)
|
||
|
}
|
||
|
|
||
|
data, err := os.ReadFile(p)
|
||
|
if err != nil {
|
||
|
return 0, fmt.Errorf("reading file %s: %w", p, err)
|
||
|
}
|
||
|
|
||
|
et := bytes.TrimSpace(data)
|
||
|
return strconv.ParseUint(string(et), 10, 64)
|
||
|
}
|
||
|
|
||
|
// Probe BPF perf link.
|
||
|
//
|
||
|
// https://elixir.bootlin.com/linux/v5.16.8/source/kernel/bpf/syscall.c#L4307
|
||
|
// https://github.com/torvalds/linux/commit/b89fbfbb854c9afc3047e8273cc3a694650b802e
|
||
|
var haveBPFLinkPerfEvent = internal.FeatureTest("bpf_link_perf_event", "5.15", func() error {
|
||
|
prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
|
||
|
Name: "probe_bpf_perf_link",
|
||
|
Type: ebpf.Kprobe,
|
||
|
Instructions: asm.Instructions{
|
||
|
asm.Mov.Imm(asm.R0, 0),
|
||
|
asm.Return(),
|
||
|
},
|
||
|
License: "MIT",
|
||
|
})
|
||
|
if err != nil {
|
||
|
return err
|
||
|
}
|
||
|
defer prog.Close()
|
||
|
|
||
|
_, err = sys.LinkCreatePerfEvent(&sys.LinkCreatePerfEventAttr{
|
||
|
ProgFd: uint32(prog.FD()),
|
||
|
AttachType: sys.BPF_PERF_EVENT,
|
||
|
})
|
||
|
if errors.Is(err, unix.EINVAL) {
|
||
|
return internal.ErrNotSupported
|
||
|
}
|
||
|
if errors.Is(err, unix.EBADF) {
|
||
|
return nil
|
||
|
}
|
||
|
return err
|
||
|
})
|
||
|
|
||
|
// isValidTraceID implements the equivalent of a regex match
|
||
|
// against "^[a-zA-Z_][0-9a-zA-Z_]*$".
|
||
|
//
|
||
|
// Trace event groups, names and kernel symbols must adhere to this set
|
||
|
// of characters. Non-empty, first character must not be a number, all
|
||
|
// characters must be alphanumeric or underscore.
|
||
|
func isValidTraceID(s string) bool {
|
||
|
if len(s) < 1 {
|
||
|
return false
|
||
|
}
|
||
|
for i, c := range []byte(s) {
|
||
|
switch {
|
||
|
case c >= 'a' && c <= 'z':
|
||
|
case c >= 'A' && c <= 'Z':
|
||
|
case c == '_':
|
||
|
case i > 0 && c >= '0' && c <= '9':
|
||
|
|
||
|
default:
|
||
|
return false
|
||
|
}
|
||
|
}
|
||
|
|
||
|
return true
|
||
|
}
|