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link: (u|k)probe: don't treat EINVAL as os.ErrNotExist #751

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merged 2 commits into from Jul 29, 2022
Merged

link: (u|k)probe: don't treat EINVAL as os.ErrNotExist #751

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9bd82c7
link: don't treat EINVAL from perf_event_open as ENOENT
lmb Jul 20, 2022
375841a
link: sync PMU and tracefs error strings
ti-mo Jul 28, 2022
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50 changes: 29 additions & 21 deletions link/kprobe.go
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Expand Up @@ -123,6 +123,9 @@ func Kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error
// 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.
//
// On kernels 5.10 and earlier, setting a kretprobe on a nonexistent symbol
// incorrectly returns unix.EINVAL instead of os.ErrNotExist.
func Kretprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions) (Link, error) {
k, err := kprobe(symbol, prog, opts, true)
if err != nil {
Expand Down Expand Up @@ -194,7 +197,7 @@ func kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions, ret bool) (*

// Use kprobe PMU if the kernel has it available.
tp, err := pmuKprobe(args)
if errors.Is(err, os.ErrNotExist) {
if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
args.symbol = platformPrefix(symbol)
tp, err = pmuKprobe(args)
}
Expand All @@ -208,7 +211,7 @@ func kprobe(symbol string, prog *ebpf.Program, opts *KprobeOptions, ret bool) (*
// Use tracefs if kprobe PMU is missing.
args.symbol = symbol
tp, err = tracefsKprobe(args)
if errors.Is(err, os.ErrNotExist) {
if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
args.symbol = platformPrefix(symbol)
tp, err = tracefsKprobe(args)
}
Expand Down Expand Up @@ -250,8 +253,9 @@ func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
}

var (
attr unix.PerfEventAttr
sp unsafe.Pointer
attr unix.PerfEventAttr
sp unsafe.Pointer
token string
)
switch typ {
case kprobeType:
Expand All @@ -261,6 +265,8 @@ func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
return nil, err
}

token = kprobeToken(args)

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.
Expand All @@ -280,6 +286,8 @@ func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
config |= args.refCtrOffset << uprobeRefCtrOffsetShift
}

token = uprobeToken(args)

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
Expand All @@ -299,27 +307,27 @@ func pmuProbe(typ probeType, args probeArgs) (*perfEvent, error) {
// 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)
return nil, fmt.Errorf("token %s: older kernels don't accept dots: %w", token, 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)
// when trying to create a retprobe for a missing symbol.
if errors.Is(err, os.ErrNotExist) {
return nil, fmt.Errorf("token %s: not found: %w", token, err)
}
// Since commit ab105a4fb894, EILSEQ is returned when a kprobe sym+offset is resolved
// to an invalid insn boundary. The exact conditions that trigger this error are
// arch specific however.
if errors.Is(err, unix.EILSEQ) {
return nil, fmt.Errorf("symbol '%s+%#x' not found (bad insn boundary): %w", args.symbol, args.offset, os.ErrNotExist)
return nil, fmt.Errorf("token %s: bad insn boundary: %w", token, os.ErrNotExist)
}
// Since at least commit cb9a19fe4aa51, ENOTSUPP is returned
// when attempting to set a uprobe on a trap instruction.
if errors.Is(err, sys.ENOTSUPP) {
return nil, fmt.Errorf("failed setting uprobe on offset %#x (possible trap insn): %w", args.offset, err)
return nil, fmt.Errorf("token %s: failed setting uprobe on offset %#x (possible trap insn): %w", token, args.offset, err)
}

if err != nil {
return nil, fmt.Errorf("opening perf event: %w", err)
return nil, fmt.Errorf("token %s: opening perf event: %w", token, err)
}

// Ensure the string pointer is not collected before PerfEventOpen returns.
Expand Down Expand Up @@ -455,16 +463,15 @@ func createTraceFSProbeEvent(typ probeType, args probeArgs) error {
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)
// when trying to create a retprobe for a missing symbol.
if errors.Is(err, os.ErrNotExist) {
return fmt.Errorf("token %s: not found: %w", token, err)
}
// Since commit ab105a4fb894, -EILSEQ is returned when a kprobe sym+offset is resolved
// to an invalid insn boundary.
// Since commit ab105a4fb894, EILSEQ is returned when a kprobe sym+offset is resolved
// to an invalid insn boundary. The exact conditions that trigger this error are
// arch specific however.
if errors.Is(err, syscall.EILSEQ) {
return fmt.Errorf("token %s: bad insn boundary: %w", token, os.ErrNotExist)
}
Expand All @@ -473,8 +480,9 @@ func createTraceFSProbeEvent(typ probeType, args probeArgs) error {
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 fmt.Errorf("token %s: writing '%s': %w", token, pe, err)
}

return nil
Expand Down
8 changes: 6 additions & 2 deletions link/kprobe_test.go
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Expand Up @@ -86,7 +86,9 @@ func TestKretprobe(t *testing.T) {
c := qt.New(t)

k, err := Kretprobe("bogus", prog, nil)
c.Assert(err, qt.ErrorIs, os.ErrNotExist, qt.Commentf("got error: %s", err))
if !(errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL)) {
t.Fatal(err)
}
if k != nil {
k.Close()
}
Expand Down Expand Up @@ -215,7 +217,9 @@ func TestKprobeTraceFS(t *testing.T) {
// of ENOENT, but only for kretprobes.
args.ret = true
err = createTraceFSProbeEvent(kprobeType, args)
c.Assert(errors.Is(err, os.ErrNotExist), qt.IsTrue, qt.Commentf("got error: %s", err))
if !(errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL)) {
t.Fatal(err)
}
}

func BenchmarkKprobeCreateTraceFS(b *testing.B) {
Expand Down