github.com/nicocha30/gvisor-ligolo@v0.0.0-20230726075806-989fa2c0a413/pkg/flipcall/flipcall_unsafe.go (about)

     1  // Copyright 2019 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package flipcall
    16  
    17  import (
    18  	"reflect"
    19  	"unsafe"
    20  
    21  	"github.com/nicocha30/gvisor-ligolo/pkg/atomicbitops"
    22  	"github.com/nicocha30/gvisor-ligolo/pkg/sync"
    23  )
    24  
    25  // Packets consist of a 16-byte header followed by an arbitrarily-sized
    26  // datagram. The header consists of:
    27  //
    28  //   - A 4-byte native-endian connection state.
    29  //
    30  //   - A 4-byte native-endian datagram length in bytes.
    31  //
    32  //   - 8 reserved bytes.
    33  const (
    34  	// PacketHeaderBytes is the size of a flipcall packet header in bytes. The
    35  	// maximum datagram size supported by a flipcall connection is equal to the
    36  	// length of the packet window minus PacketHeaderBytes.
    37  	//
    38  	// PacketHeaderBytes is exported to support its use in constant
    39  	// expressions. Non-constant expressions may prefer to use
    40  	// PacketWindowLengthForDataCap().
    41  	PacketHeaderBytes = 16
    42  )
    43  
    44  func (ep *Endpoint) connState() *atomicbitops.Uint32 {
    45  	return (*atomicbitops.Uint32)(unsafe.Pointer(ep.packet))
    46  }
    47  
    48  func (ep *Endpoint) dataLen() *atomicbitops.Uint32 {
    49  	return (*atomicbitops.Uint32)(unsafe.Pointer(ep.packet + 4))
    50  }
    51  
    52  // Data returns the datagram part of ep's packet window as a byte slice.
    53  //
    54  // Note that the packet window is shared with the potentially-untrusted peer
    55  // Endpoint, which may concurrently mutate the contents of the packet window.
    56  // Thus:
    57  //
    58  //   - Readers must not assume that two reads of the same byte in Data() will
    59  //     return the same result. In other words, readers should read any given byte
    60  //     in Data() at most once.
    61  //
    62  //   - Writers must not assume that they will read back the same data that they
    63  //     have written. In other words, writers should avoid reading from Data() at
    64  //     all.
    65  func (ep *Endpoint) Data() (bs []byte) {
    66  	bshdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
    67  	bshdr.Data = ep.packet + PacketHeaderBytes
    68  	bshdr.Len = int(ep.dataCap)
    69  	bshdr.Cap = int(ep.dataCap)
    70  	return
    71  }
    72  
    73  // ioSync is a dummy variable used to indicate synchronization to the Go race
    74  // detector. Compare syscall.ioSync.
    75  var ioSync int64
    76  
    77  func raceBecomeActive() {
    78  	if sync.RaceEnabled {
    79  		sync.RaceAcquire(unsafe.Pointer(&ioSync))
    80  	}
    81  }
    82  
    83  func raceBecomeInactive() {
    84  	if sync.RaceEnabled {
    85  		sync.RaceReleaseMerge(unsafe.Pointer(&ioSync))
    86  	}
    87  }