github.com/sagernet/gvisor@v0.0.0-20240428053021-e691de28565f/pkg/tcpip/link/fdbased/mmap_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  //go:build (linux && amd64) || (linux && arm64)
    16  // +build linux,amd64 linux,arm64
    17  
    18  package fdbased
    19  
    20  import (
    21  	"fmt"
    22  	"unsafe"
    23  
    24  	"golang.org/x/sys/unix"
    25  	"github.com/sagernet/gvisor/pkg/atomicbitops"
    26  	"github.com/sagernet/gvisor/pkg/tcpip/link/stopfd"
    27  )
    28  
    29  // tPacketHdrlen is the TPACKET_HDRLEN variable defined in <linux/if_packet.h>.
    30  var tPacketHdrlen = tPacketAlign(unsafe.Sizeof(tPacketHdr{}) + unsafe.Sizeof(unix.RawSockaddrLinklayer{}))
    31  
    32  // tpStatus returns the frame status field.
    33  // The status is concurrently updated by the kernel as a result we must
    34  // use atomic operations to prevent races.
    35  func (t tPacketHdr) tpStatus() uint32 {
    36  	hdr := unsafe.Pointer(&t[0])
    37  	statusPtr := unsafe.Pointer(uintptr(hdr) + uintptr(tpStatusOffset))
    38  	return (*atomicbitops.Uint32)(statusPtr).Load()
    39  }
    40  
    41  // setTPStatus set's the frame status to the provided status.
    42  // The status is concurrently updated by the kernel as a result we must
    43  // use atomic operations to prevent races.
    44  func (t tPacketHdr) setTPStatus(status uint32) {
    45  	hdr := unsafe.Pointer(&t[0])
    46  	statusPtr := unsafe.Pointer(uintptr(hdr) + uintptr(tpStatusOffset))
    47  	(*atomicbitops.Uint32)(statusPtr).Store(status)
    48  }
    49  
    50  func newPacketMMapDispatcher(fd int, e *endpoint) (linkDispatcher, error) {
    51  	stopFD, err := stopfd.New()
    52  	if err != nil {
    53  		return nil, err
    54  	}
    55  	d := &packetMMapDispatcher{
    56  		StopFD: stopFD,
    57  		fd:     fd,
    58  		e:      e,
    59  	}
    60  	pageSize := unix.Getpagesize()
    61  	if tpBlockSize%pageSize != 0 {
    62  		return nil, fmt.Errorf("tpBlockSize: %d is not page aligned, pagesize: %d", tpBlockSize, pageSize)
    63  	}
    64  	tReq := tPacketReq{
    65  		tpBlockSize: uint32(tpBlockSize),
    66  		tpBlockNR:   uint32(tpBlockNR),
    67  		tpFrameSize: uint32(tpFrameSize),
    68  		tpFrameNR:   uint32(tpFrameNR),
    69  	}
    70  	// Setup PACKET_RX_RING.
    71  	if err := setsockopt(d.fd, unix.SOL_PACKET, unix.PACKET_RX_RING, unsafe.Pointer(&tReq), unsafe.Sizeof(tReq)); err != nil {
    72  		return nil, fmt.Errorf("failed to enable PACKET_RX_RING: %v", err)
    73  	}
    74  	// Let's mmap the blocks.
    75  	sz := tpBlockSize * tpBlockNR
    76  	buf, err := unix.Mmap(d.fd, 0, sz, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
    77  	if err != nil {
    78  		return nil, fmt.Errorf("unix.Mmap(...,0, %v, ...) failed = %v", sz, err)
    79  	}
    80  	d.ringBuffer = buf
    81  	return d, nil
    82  }
    83  
    84  func setsockopt(fd, level, name int, val unsafe.Pointer, vallen uintptr) error {
    85  	if _, _, errno := unix.Syscall6(unix.SYS_SETSOCKOPT, uintptr(fd), uintptr(level), uintptr(name), uintptr(val), vallen, 0); errno != 0 {
    86  		return error(errno)
    87  	}
    88  
    89  	return nil
    90  }