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// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// +build linux,amd64 linux,arm64
package fdbased
import (
"encoding/binary"
"syscall"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/link/rawfile"
)
const (
tPacketAlignment = uintptr(16)
tpStatusKernel = 0
tpStatusUser = 1
tpStatusCopy = 2
tpStatusLosing = 4
)
// We overallocate the frame size to accommodate space for the
// TPacketHdr+RawSockAddrLinkLayer+MAC header and any padding.
//
// Memory allocated for the ring buffer: tpBlockSize * tpBlockNR = 2 MiB
//
// NOTE:
// Frames need to be aligned at 16 byte boundaries.
// BlockSize needs to be page aligned.
//
// For details see PACKET_MMAP setting constraints in
// https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt
const (
tpFrameSize = 65536 + 128
tpBlockSize = tpFrameSize * 32
tpBlockNR = 1
tpFrameNR = (tpBlockSize * tpBlockNR) / tpFrameSize
)
// tPacketAlign aligns the pointer v at a tPacketAlignment boundary. Direct
// translation of the TPACKET_ALIGN macro in <linux/if_packet.h>.
func tPacketAlign(v uintptr) uintptr {
return (v + tPacketAlignment - 1) & uintptr(^(tPacketAlignment - 1))
}
// tPacketReq is the tpacket_req structure as described in
// https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt
type tPacketReq struct {
tpBlockSize uint32
tpBlockNR uint32
tpFrameSize uint32
tpFrameNR uint32
}
// tPacketHdr is tpacket_hdr structure as described in <linux/if_packet.h>
type tPacketHdr []byte
const (
tpStatusOffset = 0
tpLenOffset = 8
tpSnapLenOffset = 12
tpMacOffset = 16
tpNetOffset = 18
tpSecOffset = 20
tpUSecOffset = 24
)
func (t tPacketHdr) tpLen() uint32 {
return binary.LittleEndian.Uint32(t[tpLenOffset:])
}
func (t tPacketHdr) tpSnapLen() uint32 {
return binary.LittleEndian.Uint32(t[tpSnapLenOffset:])
}
func (t tPacketHdr) tpMac() uint16 {
return binary.LittleEndian.Uint16(t[tpMacOffset:])
}
func (t tPacketHdr) tpNet() uint16 {
return binary.LittleEndian.Uint16(t[tpNetOffset:])
}
func (t tPacketHdr) tpSec() uint32 {
return binary.LittleEndian.Uint32(t[tpSecOffset:])
}
func (t tPacketHdr) tpUSec() uint32 {
return binary.LittleEndian.Uint32(t[tpUSecOffset:])
}
func (t tPacketHdr) Payload() []byte {
return t[uint32(t.tpMac()) : uint32(t.tpMac())+t.tpSnapLen()]
}
// packetMMapDispatcher uses PACKET_RX_RING's to read/dispatch inbound packets.
// See: mmap_amd64_unsafe.go for implementation details.
type packetMMapDispatcher struct {
// fd is the file descriptor used to send and receive packets.
fd int
// e is the endpoint this dispatcher is attached to.
e *endpoint
// ringBuffer is only used when PacketMMap dispatcher is used and points
// to the start of the mmapped PACKET_RX_RING buffer.
ringBuffer []byte
// ringOffset is the current offset into the ring buffer where the next
// inbound packet will be placed by the kernel.
ringOffset int
}
func (d *packetMMapDispatcher) readMMappedPacket() ([]byte, *tcpip.Error) {
hdr := tPacketHdr(d.ringBuffer[d.ringOffset*tpFrameSize:])
for hdr.tpStatus()&tpStatusUser == 0 {
event := rawfile.PollEvent{
FD: int32(d.fd),
Events: unix.POLLIN | unix.POLLERR,
}
if _, errno := rawfile.BlockingPoll(&event, 1, nil); errno != 0 {
if errno == syscall.EINTR {
continue
}
return nil, rawfile.TranslateErrno(errno)
}
if hdr.tpStatus()&tpStatusCopy != 0 {
// This frame is truncated so skip it after flipping the
// buffer to the kernel.
hdr.setTPStatus(tpStatusKernel)
d.ringOffset = (d.ringOffset + 1) % tpFrameNR
hdr = (tPacketHdr)(d.ringBuffer[d.ringOffset*tpFrameSize:])
continue
}
}
// Copy out the packet from the mmapped frame to a locally owned buffer.
pkt := make([]byte, hdr.tpSnapLen())
copy(pkt, hdr.Payload())
// Release packet to kernel.
hdr.setTPStatus(tpStatusKernel)
d.ringOffset = (d.ringOffset + 1) % tpFrameNR
return pkt, nil
}
// dispatch reads packets from an mmaped ring buffer and dispatches them to the
// network stack.
func (d *packetMMapDispatcher) dispatch() (bool, *tcpip.Error) {
pkt, err := d.readMMappedPacket()
if err != nil {
return false, err
}
var (
p tcpip.NetworkProtocolNumber
remote, local tcpip.LinkAddress
eth header.Ethernet
)
if d.e.hdrSize > 0 {
eth = header.Ethernet(pkt)
p = eth.Type()
remote = eth.SourceAddress()
local = eth.DestinationAddress()
} else {
// We don't get any indication of what the packet is, so try to guess
// if it's an IPv4 or IPv6 packet.
switch header.IPVersion(pkt) {
case header.IPv4Version:
p = header.IPv4ProtocolNumber
case header.IPv6Version:
p = header.IPv6ProtocolNumber
default:
return true, nil
}
}
pkt = pkt[d.e.hdrSize:]
d.e.dispatcher.DeliverNetworkPacket(d.e, remote, local, p, buffer.NewVectorisedView(len(pkt), []buffer.View{buffer.View(pkt)}), buffer.View(eth))
return true, nil
}
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