wintun: ring management moved to wintun.dll

Signed-off-by: Simon Rozman <simon@rozman.si>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

4 files changed, 147 insertions, 214 deletions

diff --git a/tun/tun_windows.go b/tun/tun_windows.go
index 684d6f0..63eb812 100644
--- a/tun/tun_windows.go
+++ b/tun/tun_windows.go
@@ -9,10 +9,9 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"sync"
 	"sync/atomic"
 	"time"
-	"unsafe"
+	_ "unsafe"
 
 	"golang.org/x/sys/windows"
 
@@ -40,8 +39,8 @@ type NativeTun struct {
 	errors    chan error
 	forcedMTU int
 	rate      rateJuggler
-	rings     *wintun.RingDescriptor
-	writeLock sync.Mutex
+	session   wintun.Session
+	readWait  windows.Handle
 }
 
 var WintunPool *wintun.Pool
@@ -103,17 +102,13 @@ func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID, mtu
 		forcedMTU: forcedMTU,
 	}
 
-	tun.rings, err = wintun.NewRingDescriptor()
+	tun.session, err = wt.StartSession(0x800000) // Ring capacity, 8 MiB
 	if err != nil {
-		tun.Close()
-		return nil, fmt.Errorf("Error creating events: %v", err)
-	}
-
-	tun.handle, err = tun.wt.Register(tun.rings)
-	if err != nil {
-		tun.Close()
-		return nil, fmt.Errorf("Error registering rings: %v", err)
+		_, err = tun.wt.Delete(false)
+		close(tun.events)
+		return nil, fmt.Errorf("Error starting session: %v", err)
 	}
+	tun.readWait = tun.session.ReadWaitEvent()
 	return tun, nil
 }
 
@@ -131,13 +126,7 @@ func (tun *NativeTun) Events() chan Event {
 
 func (tun *NativeTun) Close() error {
 	tun.close = true
-	if tun.rings.Send.TailMoved != 0 {
-		windows.SetEvent(tun.rings.Send.TailMoved) // wake the reader if it's sleeping
-	}
-	if tun.handle != windows.InvalidHandle {
-		windows.CloseHandle(tun.handle)
-	}
-	tun.rings.Close()
+	tun.session.End()
 	var err error
 	if tun.wt != nil {
 		_, err = tun.wt.Delete(false)
@@ -164,56 +153,34 @@ retry:
 		return 0, err
 	default:
 	}
-	if tun.close {
-		return 0, os.ErrClosed
-	}
-
-	buffHead := atomic.LoadUint32(&tun.rings.Send.Ring.Head)
-	if buffHead >= wintun.PacketCapacity {
-		return 0, os.ErrClosed
-	}
-
 	start := nanotime()
 	shouldSpin := atomic.LoadUint64(&tun.rate.current) >= spinloopRateThreshold && uint64(start-atomic.LoadInt64(&tun.rate.nextStartTime)) <= rateMeasurementGranularity*2
-	var buffTail uint32
 	for {
-		buffTail = atomic.LoadUint32(&tun.rings.Send.Ring.Tail)
-		if buffHead != buffTail {
-			break
-		}
 		if tun.close {
 			return 0, os.ErrClosed
 		}
-		if !shouldSpin || uint64(nanotime()-start) >= spinloopDuration {
-			windows.WaitForSingleObject(tun.rings.Send.TailMoved, windows.INFINITE)
-			goto retry
+		packet, err := tun.session.ReceivePacket()
+		switch err {
+		case nil:
+			packetSize := len(packet)
+			copy(buff[offset:], packet)
+			tun.session.ReleaseReceivePacket(packet)
+			tun.rate.update(uint64(packetSize))
+			return packetSize, nil
+		case windows.ERROR_NO_MORE_ITEMS:
+			if !shouldSpin || uint64(nanotime()-start) >= spinloopDuration {
+				windows.WaitForSingleObject(tun.readWait, windows.INFINITE)
+				goto retry
+			}
+			procyield(1)
+			continue
+		case windows.ERROR_HANDLE_EOF:
+			return 0, os.ErrClosed
+		case windows.ERROR_INVALID_DATA:
+			return 0, errors.New("Send ring corrupt")
 		}
-		procyield(1)
-	}
-	if buffTail >= wintun.PacketCapacity {
-		return 0, os.ErrClosed
-	}
-
-	buffContent := tun.rings.Send.Ring.Wrap(buffTail - buffHead)
-	if buffContent < uint32(unsafe.Sizeof(wintun.PacketHeader{})) {
-		return 0, errors.New("incomplete packet header in send ring")
-	}
-
-	packet := (*wintun.Packet)(unsafe.Pointer(&tun.rings.Send.Ring.Data[buffHead]))
-	if packet.Size > wintun.PacketSizeMax {
-		return 0, errors.New("packet too big in send ring")
-	}
-
-	alignedPacketSize := wintun.PacketAlign(uint32(unsafe.Sizeof(wintun.PacketHeader{})) + packet.Size)
-	if alignedPacketSize > buffContent {
-		return 0, errors.New("incomplete packet in send ring")
+		return 0, fmt.Errorf("Read failed: %v", err)
 	}
-
-	copy(buff[offset:], packet.Data[:packet.Size])
-	buffHead = tun.rings.Send.Ring.Wrap(buffHead + alignedPacketSize)
-	atomic.StoreUint32(&tun.rings.Send.Ring.Head, buffHead)
-	tun.rate.update(uint64(packet.Size))
-	return int(packet.Size), nil
 }
 
 func (tun *NativeTun) Flush() error {
@@ -225,36 +192,22 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 		return 0, os.ErrClosed
 	}
 
-	packetSize := uint32(len(buff) - offset)
+	packetSize := len(buff) - offset
 	tun.rate.update(uint64(packetSize))
-	alignedPacketSize := wintun.PacketAlign(uint32(unsafe.Sizeof(wintun.PacketHeader{})) + packetSize)
 
-	tun.writeLock.Lock()
-	defer tun.writeLock.Unlock()
-
-	buffHead := atomic.LoadUint32(&tun.rings.Receive.Ring.Head)
-	if buffHead >= wintun.PacketCapacity {
-		return 0, os.ErrClosed
+	packet, err := tun.session.AllocateSendPacket(packetSize)
+	if err == nil {
+		copy(packet, buff[offset:])
+		tun.session.SendPacket(packet)
+		return packetSize, nil
 	}
-
-	buffTail := atomic.LoadUint32(&tun.rings.Receive.Ring.Tail)
-	if buffTail >= wintun.PacketCapacity {
+	switch err {
+	case windows.ERROR_HANDLE_EOF:
 		return 0, os.ErrClosed
-	}
-
-	buffSpace := tun.rings.Receive.Ring.Wrap(buffHead - buffTail - wintun.PacketAlignment)
-	if alignedPacketSize > buffSpace {
+	case windows.ERROR_BUFFER_OVERFLOW:
 		return 0, nil // Dropping when ring is full.
 	}
-
-	packet := (*wintun.Packet)(unsafe.Pointer(&tun.rings.Receive.Ring.Data[buffTail]))
-	packet.Size = packetSize
-	copy(packet.Data[:packetSize], buff[offset:])
-	atomic.StoreUint32(&tun.rings.Receive.Ring.Tail, tun.rings.Receive.Ring.Wrap(buffTail+alignedPacketSize))
-	if atomic.LoadInt32(&tun.rings.Receive.Ring.Alertable) != 0 {
-		windows.SetEvent(tun.rings.Receive.TailMoved)
-	}
-	return int(packetSize), nil
+	return 0, fmt.Errorf("Write failed: %v", err)
 }
 
 // LUID returns Windows interface instance ID.
diff --git a/tun/wintun/ring_windows.go b/tun/wintun/ring_windows.go
deleted file mode 100644
index ed460fb..0000000
--- a/tun/wintun/ring_windows.go
+++ /dev/null
@@ -1,117 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2020 WireGuard LLC. All Rights Reserved.
- */
-
-package wintun
-
-import (
-	"runtime"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-const (
-	PacketAlignment    = 4        // Number of bytes packets are aligned to in rings
-	PacketSizeMax      = 0xffff   // Maximum packet size
-	PacketCapacity     = 0x800000 // Ring capacity, 8MiB
-	PacketTrailingSize = uint32(unsafe.Sizeof(PacketHeader{})) + ((PacketSizeMax + (PacketAlignment - 1)) &^ (PacketAlignment - 1)) - PacketAlignment
-	ioctlRegisterRings = (51820 << 16) | (0x970 << 2) | 0 /*METHOD_BUFFERED*/ | (0x3 /*FILE_READ_DATA | FILE_WRITE_DATA*/ << 14)
-)
-
-type PacketHeader struct {
-	Size uint32
-}
-
-type Packet struct {
-	PacketHeader
-	Data [PacketSizeMax]byte
-}
-
-type Ring struct {
-	Head      uint32
-	Tail      uint32
-	Alertable int32
-	Data      [PacketCapacity + PacketTrailingSize]byte
-}
-
-type RingDescriptor struct {
-	Send, Receive struct {
-		Size      uint32
-		Ring      *Ring
-		TailMoved windows.Handle
-	}
-}
-
-// Wrap returns value modulo ring capacity
-func (rb *Ring) Wrap(value uint32) uint32 {
-	return value & (PacketCapacity - 1)
-}
-
-// Aligns a packet size to PacketAlignment
-func PacketAlign(size uint32) uint32 {
-	return (size + (PacketAlignment - 1)) &^ (PacketAlignment - 1)
-}
-
-func NewRingDescriptor() (descriptor *RingDescriptor, err error) {
-	descriptor = new(RingDescriptor)
-	allocatedRegion, err := windows.VirtualAlloc(0, unsafe.Sizeof(Ring{})*2, windows.MEM_COMMIT|windows.MEM_RESERVE, windows.PAGE_READWRITE)
-	if err != nil {
-		return
-	}
-	defer func() {
-		if err != nil {
-			descriptor.free()
-			descriptor = nil
-		}
-	}()
-	descriptor.Send.Size = uint32(unsafe.Sizeof(Ring{}))
-	descriptor.Send.Ring = (*Ring)(unsafe.Pointer(allocatedRegion))
-	descriptor.Send.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
-	if err != nil {
-		return
-	}
-
-	descriptor.Receive.Size = uint32(unsafe.Sizeof(Ring{}))
-	descriptor.Receive.Ring = (*Ring)(unsafe.Pointer(allocatedRegion + unsafe.Sizeof(Ring{})))
-	descriptor.Receive.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
-	if err != nil {
-		windows.CloseHandle(descriptor.Send.TailMoved)
-		return
-	}
-	runtime.SetFinalizer(descriptor, func(d *RingDescriptor) { d.free() })
-	return
-}
-
-func (descriptor *RingDescriptor) free() {
-	if descriptor.Send.Ring != nil {
-		windows.VirtualFree(uintptr(unsafe.Pointer(descriptor.Send.Ring)), 0, windows.MEM_RELEASE)
-		descriptor.Send.Ring = nil
-		descriptor.Receive.Ring = nil
-	}
-}
-
-func (descriptor *RingDescriptor) Close() {
-	if descriptor.Send.TailMoved != 0 {
-		windows.CloseHandle(descriptor.Send.TailMoved)
-		descriptor.Send.TailMoved = 0
-	}
-	if descriptor.Send.TailMoved != 0 {
-		windows.CloseHandle(descriptor.Receive.TailMoved)
-		descriptor.Receive.TailMoved = 0
-	}
-}
-
-func (wintun *Adapter) Register(descriptor *RingDescriptor) (windows.Handle, error) {
-	handle, err := wintun.OpenAdapterDeviceObject()
-	if err != nil {
-		return 0, err
-	}
-	var bytesReturned uint32
-	err = windows.DeviceIoControl(handle, ioctlRegisterRings, (*byte)(unsafe.Pointer(descriptor)), uint32(unsafe.Sizeof(*descriptor)), nil, 0, &bytesReturned, nil)
-	if err != nil {
-		return 0, err
-	}
-	return handle, nil
-}
diff --git a/tun/wintun/session_windows.go b/tun/wintun/session_windows.go
new file mode 100644
index 0000000..1619e5a
--- /dev/null
+++ b/tun/wintun/session_windows.go
@@ -0,0 +1,108 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2020 WireGuard LLC. All Rights Reserved.
+ */
+
+package wintun
+
+import (
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+type Session struct {
+	handle uintptr
+}
+
+const (
+	PacketSizeMax   = 0xffff    // Maximum packet size
+	RingCapacityMin = 0x20000   // Minimum ring capacity (128 kiB)
+	RingCapacityMax = 0x4000000 // Maximum ring capacity (64 MiB)
+)
+
+// Packet with data
+type Packet struct {
+	Next *Packet              // Pointer to next packet in queue
+	Size uint32               // Size of packet (max WINTUN_MAX_IP_PACKET_SIZE)
+	Data *[PacketSizeMax]byte // Pointer to layer 3 IPv4 or IPv6 packet
+}
+
+var (
+	procWintunAllocateSendPacket   = modwintun.NewProc("WintunAllocateSendPacket").Addr()
+	procWintunEndSession           = modwintun.NewProc("WintunEndSession")
+	procWintunGetReadWaitEvent     = modwintun.NewProc("WintunGetReadWaitEvent")
+	procWintunReceivePacket        = modwintun.NewProc("WintunReceivePacket").Addr()
+	procWintunReleaseReceivePacket = modwintun.NewProc("WintunReleaseReceivePacket").Addr()
+	procWintunSendPacket           = modwintun.NewProc("WintunSendPacket").Addr()
+	procWintunStartSession         = modwintun.NewProc("WintunStartSession")
+)
+
+func (wintun *Adapter) StartSession(capacity uint32) (session Session, err error) {
+	r0, _, e1 := syscall.Syscall(procWintunStartSession.Addr(), 2, uintptr(wintun.handle), uintptr(capacity), 0)
+	if r0 == 0 {
+		err = e1
+	} else {
+		session = Session{r0}
+	}
+	return
+}
+
+func (session Session) End() {
+	syscall.Syscall(procWintunEndSession.Addr(), 1, session.handle, 0, 0)
+	session.handle = 0
+}
+
+func (session Session) ReadWaitEvent() (handle windows.Handle) {
+	r0, _, _ := syscall.Syscall(procWintunGetReadWaitEvent.Addr(), 1, session.handle, 0, 0)
+	handle = windows.Handle(r0)
+	return
+}
+
+func (session Session) ReceivePacket() (packet []byte, err error) {
+	var packetSize uint32
+	r0, _, e1 := syscall.Syscall(procWintunReceivePacket, 2, session.handle, uintptr(unsafe.Pointer(&packetSize)), 0)
+	if r0 == 0 {
+		err = e1
+		return
+	}
+	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	return
+}
+
+func (session Session) ReleaseReceivePacket(packet []byte) {
+	syscall.Syscall(procWintunReleaseReceivePacket, 2, session.handle, uintptr(unsafe.Pointer(&packet[0])), 0)
+}
+
+func (session Session) AllocateSendPacket(packetSize int) (packet []byte, err error) {
+	r0, _, e1 := syscall.Syscall(procWintunAllocateSendPacket, 2, session.handle, uintptr(packetSize), 0)
+	if r0 == 0 {
+		err = e1
+		return
+	}
+	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	return
+}
+
+func (session Session) SendPacket(packet []byte) {
+	syscall.Syscall(procWintunSendPacket, 2, session.handle, uintptr(unsafe.Pointer(&packet[0])), 0)
+}
+
+// unsafeSlice updates the slice slicePtr to be a slice
+// referencing the provided data with its length & capacity set to
+// lenCap.
+//
+// TODO: when Go 1.16 or Go 1.17 is the minimum supported version,
+// update callers to use unsafe.Slice instead of this.
+func unsafeSlice(slicePtr, data unsafe.Pointer, lenCap int) {
+	type sliceHeader struct {
+		Data unsafe.Pointer
+		Len  int
+		Cap  int
+	}
+	h := (*sliceHeader)(slicePtr)
+	h.Data = data
+	h.Len = lenCap
+	h.Cap = lenCap
+}
diff --git a/tun/wintun/wintun_windows.go b/tun/wintun/wintun_windows.go
index ac33579..e7ba8b6 100644
--- a/tun/wintun/wintun_windows.go
+++ b/tun/wintun/wintun_windows.go
@@ -45,7 +45,6 @@ var (
 	procWintunGetAdapterLUID          = modwintun.NewProc("WintunGetAdapterLUID")
 	procWintunGetAdapterName          = modwintun.NewProc("WintunGetAdapterName")
 	procWintunGetRunningDriverVersion = modwintun.NewProc("WintunGetRunningDriverVersion")
-	procWintunOpenAdapterDeviceObject = modwintun.NewProc("WintunOpenAdapterDeviceObject")
 	procWintunSetAdapterName          = modwintun.NewProc("WintunSetAdapterName")
 	procWintunSetLogger               = modwintun.NewProc("WintunSetLogger")
 )
@@ -210,16 +209,6 @@ func RunningVersion() (version uint32, err error) {
 	return
 }
 
-// handle returns a handle to the adapter device object. Release handle with windows.CloseHandle
-func (wintun *Adapter) OpenAdapterDeviceObject() (handle windows.Handle, err error) {
-	r0, _, e1 := syscall.Syscall(procWintunOpenAdapterDeviceObject.Addr(), 1, uintptr(wintun.handle), 0, 0)
-	handle = windows.Handle(r0)
-	if handle == windows.InvalidHandle {
-		err = e1
-	}
-	return
-}
-
 // LUID returns the LUID of the adapter.
 func (wintun *Adapter) LUID() (luid uint64) {
 	syscall.Syscall(procWintunGetAdapterLUID.Addr(), 2, uintptr(wintun.handle), uintptr(unsafe.Pointer(&luid)), 0)