GoToSocial/vendor/github.com/cilium/ebpf/link/kprobe.go

569 lines
17 KiB
Go

package link
import (
"bytes"
"crypto/rand"
"errors"
"fmt"
"os"
"path/filepath"
"runtime"
"strings"
"sync"
"syscall"
"unsafe"
"github.com/cilium/ebpf"
"github.com/cilium/ebpf/internal/sys"
"github.com/cilium/ebpf/internal/unix"
)
var (
kprobeEventsPath = filepath.Join(tracefsPath, "kprobe_events")
kprobeRetprobeBit = struct {
once sync.Once
value uint64
err error
}{}
)
type probeType uint8
type probeArgs struct {
symbol, group, path string
offset, refCtrOffset, cookie uint64
pid int
ret bool
}
// KprobeOptions defines additional parameters that will be used
// when loading Kprobes.
type KprobeOptions struct {
// Arbitrary value that can be fetched from an eBPF program
// via `bpf_get_attach_cookie()`.
//
// Needs kernel 5.15+.
Cookie uint64
// Offset of the kprobe relative to the traced symbol.
// Can be used to insert kprobes at arbitrary offsets in kernel functions,
// e.g. in places where functions have been inlined.
Offset uint64
}
const (
kprobeType probeType = iota
uprobeType
)
func (pt probeType) String() string {
if pt == kprobeType {
return "kprobe"
}
return "uprobe"
}
func (pt probeType) EventsPath() string {
if pt == kprobeType {
return kprobeEventsPath
}
return uprobeEventsPath
}
func (pt probeType) PerfEventType(ret bool) perfEventType {
if pt == kprobeType {
if ret {
return kretprobeEvent
}
return kprobeEvent
}
if ret {
return uretprobeEvent
}
return uprobeEvent
}
func (pt probeType) RetprobeBit() (uint64, error) {
if pt == kprobeType {
return kretprobeBit()
}
return uretprobeBit()
}
// Kprobe attaches the given eBPF program to a perf event that fires when the
// given kernel symbol starts executing. See /proc/kallsyms for available
// symbols. For example, printk():
//
// kp, err := Kprobe("printk", prog, nil)
//
// Losing the reference to the resulting Link (kp) will close the Kprobe
// and prevent further execution of prog. The Link must be Closed during
// program shutdown to avoid leaking system resources.
func Kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error) {
k, err := kprobe(symbol, prog, opts, false)
if err != nil {
return nil, err
}
lnk, err := attachPerfEvent(k, prog)
if err != nil {
k.Close()
return nil, err
}
return lnk, nil
}
// Kretprobe attaches the given eBPF program to a perf event that fires right
// before the given kernel symbol exits, with the function stack left intact.
// See /proc/kallsyms for available symbols. For example, printk():
//
// kp, err := Kretprobe("printk", prog, nil)
//
// Losing the reference to the resulting Link (kp) will close the Kretprobe
// and prevent further execution of prog. The Link must be Closed during
// program shutdown to avoid leaking system resources.
func Kretprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error) {
k, err := kprobe(symbol, prog, opts, true)
if err != nil {
return nil, err
}
lnk, err := attachPerfEvent(k, prog)
if err != nil {
k.Close()
return nil, err
}
return lnk, nil
}
// isValidKprobeSymbol implements the equivalent of a regex match
// against "^[a-zA-Z_][0-9a-zA-Z_.]*$".
func isValidKprobeSymbol(s string) bool {
if len(s) < 1 {
return false
}
for i, c := range []byte(s) {
switch {
case c >= 'a' && c <= 'z':
case c >= 'A' && c <= 'Z':
case c == '_':
case i > 0 && c >= '0' && c <= '9':
// Allow `.` in symbol name. GCC-compiled kernel may change symbol name
// to have a `.isra.$n` suffix, like `udp_send_skb.isra.52`.
// See: https://gcc.gnu.org/gcc-10/changes.html
case i > 0 && c == '.':
default:
return false
}
}
return true
}
// kprobe opens a perf event on the given symbol and attaches prog to it.
// If ret is true, create a kretprobe.
func kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions, ret bool) (*perfEvent, error) {
if symbol == "" {
return nil, fmt.Errorf("symbol name cannot be empty: %w", errInvalidInput)
}
if prog == nil {
return nil, fmt.Errorf("prog cannot be nil: %w", errInvalidInput)
}
if !isValidKprobeSymbol(symbol) {
return nil, fmt.Errorf("symbol '%s' must be a valid symbol in /proc/kallsyms: %w", symbol, errInvalidInput)
}
if prog.Type() != ebpf.Kprobe {
return nil, fmt.Errorf("eBPF program type %s is not a Kprobe: %w", prog.Type(), errInvalidInput)
}
args := probeArgs{
pid: perfAllThreads,
symbol: symbol,
ret: ret,
}
if opts != nil {
args.cookie = opts.Cookie
args.offset = opts.Offset
}
// Use kprobe PMU if the kernel has it available.
tp, err := pmuKprobe(args)
if errors.Is(err, os.ErrNotExist) {
args.symbol = platformPrefix(symbol)
tp, err = pmuKprobe(args)
}
if err == nil {
return tp, nil
}
if err != nil && !errors.Is(err, ErrNotSupported) {
return nil, fmt.Errorf("creating perf_kprobe PMU: %w", err)
}
// Use tracefs if kprobe PMU is missing.
args.symbol = symbol
tp, err = tracefsKprobe(args)
if errors.Is(err, os.ErrNotExist) {
args.symbol = platformPrefix(symbol)
tp, err = tracefsKprobe(args)
}
if err != nil {
return nil, fmt.Errorf("creating trace event '%s' in tracefs: %w", symbol, err)
}
return tp, nil
}
// pmuKprobe opens a perf event based on the kprobe PMU.
// Returns os.ErrNotExist if the given symbol does not exist in the kernel.
func pmuKprobe(args probeArgs) (*perfEvent, error) {
return pmuProbe(kprobeType, args)
}
// pmuProbe opens a perf event based on a Performance Monitoring Unit.
//
// Requires at least a 4.17 kernel.
// e12f03d7031a "perf/core: Implement the 'perf_kprobe' PMU"
// 33ea4b24277b "perf/core: Implement the 'perf_uprobe' PMU"
//
// Returns ErrNotSupported if the kernel doesn't support perf_[k,u]probe PMU
func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
// Getting the PMU type will fail if the kernel doesn't support
// the perf_[k,u]probe PMU.
et, err := getPMUEventType(typ)
if err != nil {
return nil, err
}
var config uint64
if args.ret {
bit, err := typ.RetprobeBit()
if err != nil {
return nil, err
}
config |= 1 << bit
}
var (
attr unix.PerfEventAttr
sp unsafe.Pointer
)
switch typ {
case kprobeType:
// Create a pointer to a NUL-terminated string for the kernel.
sp, err = unsafeStringPtr(args.symbol)
if err != nil {
return nil, err
}
attr = unix.PerfEventAttr{
// The minimum size required for PMU kprobes is PERF_ATTR_SIZE_VER1,
// since it added the config2 (Ext2) field. Use Ext2 as probe_offset.
Size: unix.PERF_ATTR_SIZE_VER1,
Type: uint32(et), // PMU event type read from sysfs
Ext1: uint64(uintptr(sp)), // Kernel symbol to trace
Ext2: args.offset, // Kernel symbol offset
Config: config, // Retprobe flag
}
case uprobeType:
sp, err = unsafeStringPtr(args.path)
if err != nil {
return nil, err
}
if args.refCtrOffset != 0 {
config |= args.refCtrOffset << uprobeRefCtrOffsetShift
}
attr = unix.PerfEventAttr{
// The minimum size required for PMU uprobes is PERF_ATTR_SIZE_VER1,
// since it added the config2 (Ext2) field. The Size field controls the
// size of the internal buffer the kernel allocates for reading the
// perf_event_attr argument from userspace.
Size: unix.PERF_ATTR_SIZE_VER1,
Type: uint32(et), // PMU event type read from sysfs
Ext1: uint64(uintptr(sp)), // Uprobe path
Ext2: args.offset, // Uprobe offset
Config: config, // RefCtrOffset, Retprobe flag
}
}
rawFd, err := unix.PerfEventOpen(&attr, args.pid, 0, -1, unix.PERF_FLAG_FD_CLOEXEC)
// On some old kernels, kprobe PMU doesn't allow `.` in symbol names and
// return -EINVAL. Return ErrNotSupported to allow falling back to tracefs.
// https://github.com/torvalds/linux/blob/94710cac0ef4/kernel/trace/trace_kprobe.c#L340-L343
if errors.Is(err, unix.EINVAL) && strings.Contains(args.symbol, ".") {
return nil, fmt.Errorf("symbol '%s+%#x': older kernels don't accept dots: %w", args.symbol, args.offset, ErrNotSupported)
}
// 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.
if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
return nil, fmt.Errorf("symbol '%s+%#x' not found: %w", args.symbol, args.offset, 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 nil, fmt.Errorf("symbol '%s+%#x' not found (bad insn boundary): %w", args.symbol, args.offset, os.ErrNotExist)
}
// Since at least commit cb9a19fe4aa51, ENOTSUPP is returned
// when attempting to set a uprobe on a trap instruction.
if errors.Is(err, unix.ENOTSUPP) {
return nil, fmt.Errorf("failed setting uprobe on offset %#x (possible trap insn): %w", args.offset, err)
}
if err != nil {
return nil, fmt.Errorf("opening perf event: %w", err)
}
// Ensure the string pointer is not collected before PerfEventOpen returns.
runtime.KeepAlive(sp)
fd, err := sys.NewFD(rawFd)
if err != nil {
return nil, err
}
// Kernel has perf_[k,u]probe PMU available, initialize perf event.
return &perfEvent{
typ: typ.PerfEventType(args.ret),
name: args.symbol,
pmuID: et,
cookie: args.cookie,
fd: fd,
}, nil
}
// tracefsKprobe creates a Kprobe tracefs entry.
func tracefsKprobe(args probeArgs) (*perfEvent, error) {
return tracefsProbe(kprobeType, args)
}
// tracefsProbe creates a trace event by writing an entry to <tracefs>/[k,u]probe_events.
// A new trace event group name is generated on every call to support creating
// multiple trace events for the same kernel or userspace symbol.
// Path and offset are only set in the case of uprobe(s) and are used to set
// the executable/library path on the filesystem and the offset where the probe is inserted.
// A perf event is then opened on the newly-created trace event and returned to the caller.
func tracefsProbe(typ probeType, args probeArgs) (_ *perfEvent, err error) {
// Generate a random string for each trace event we attempt to create.
// This value is used as the 'group' token in tracefs to allow creating
// multiple kprobe trace events with the same name.
group, err := randomGroup("ebpf")
if err != nil {
return nil, fmt.Errorf("randomizing group name: %w", err)
}
args.group = group
// Before attempting to create a trace event through tracefs,
// check if an event with the same group and name already exists.
// Kernels 4.x and earlier don't return os.ErrExist on writing a duplicate
// entry, so we need to rely on reads for detecting uniqueness.
_, err = getTraceEventID(group, args.symbol)
if err == nil {
return nil, fmt.Errorf("trace event already exists: %s/%s", group, args.symbol)
}
if err != nil && !errors.Is(err, os.ErrNotExist) {
return nil, fmt.Errorf("checking trace event %s/%s: %w", group, args.symbol, err)
}
// Create the [k,u]probe trace event using tracefs.
if err := createTraceFSProbeEvent(typ, args); err != nil {
return nil, fmt.Errorf("creating probe entry on tracefs: %w", err)
}
defer func() {
if err != nil {
// Make sure we clean up the created tracefs event when we return error.
// If a livepatch handler is already active on the symbol, the write to
// tracefs will succeed, a trace event will show up, but creating the
// perf event will fail with EBUSY.
_ = closeTraceFSProbeEvent(typ, args.group, args.symbol)
}
}()
// Get the newly-created trace event's id.
tid, err := getTraceEventID(group, args.symbol)
if err != nil {
return nil, fmt.Errorf("getting trace event id: %w", err)
}
// Kprobes are ephemeral tracepoints and share the same perf event type.
fd, err := openTracepointPerfEvent(tid, args.pid)
if err != nil {
return nil, err
}
return &perfEvent{
typ: typ.PerfEventType(args.ret),
group: group,
name: args.symbol,
tracefsID: tid,
cookie: args.cookie,
fd: fd,
}, nil
}
// createTraceFSProbeEvent creates a new ephemeral trace event by writing to
// <tracefs>/[k,u]probe_events. Returns os.ErrNotExist if symbol is not a valid
// kernel symbol, or if it is not traceable with kprobes. Returns os.ErrExist
// if a probe with the same group and symbol already exists.
func createTraceFSProbeEvent(typ probeType, args probeArgs) error {
// Open the kprobe_events file in tracefs.
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()
var pe, token string
switch typ {
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
}