1 files changed, 31 insertions, 3 deletions
diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index feb79fe0e..6fe2dd33c 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -45,7 +45,6 @@ import (
 	"sync/atomic"
 
 	"golang.org/x/sys/unix"
-	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/iovec"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -403,6 +402,35 @@ type virtioNetHdr struct {
 	csumOffset uint16
 }
 
+// marshal serializes h to a newly-allocated byte slice, in little-endian byte
+// order.
+//
+// Note: Virtio v1.0 onwards specifies little-endian as the byte ordering used
+// for general serialization. This makes it difficult to use go-marshal for
+// virtio types, as go-marshal implicitly uses the native byte ordering.
+func (h *virtioNetHdr) marshal() []byte {
+	buf := [virtioNetHdrSize]byte{
+		0: byte(h.flags),
+		1: byte(h.gsoType),
+
+		// Manually lay out the fields in little-endian byte order. Little endian =>
+		// least significant bit goes to the lower address.
+
+		2: byte(h.hdrLen),
+		3: byte(h.hdrLen >> 8),
+
+		4: byte(h.gsoSize),
+		5: byte(h.gsoSize >> 8),
+
+		6: byte(h.csumStart),
+		7: byte(h.csumStart >> 8),
+
+		8: byte(h.csumOffset),
+		9: byte(h.csumOffset >> 8),
+	}
+	return buf[:]
+}
+
 // These constants are declared in linux/virtio_net.h.
 const (
 	_VIRTIO_NET_HDR_F_NEEDS_CSUM = 1
@@ -463,7 +491,7 @@ func (e *endpoint) WritePacket(r stack.RouteInfo, protocol tcpip.NetworkProtocol
 			}
 		}
 
-		vnetHdrBuf := binary.Marshal(make([]byte, 0, virtioNetHdrSize), binary.LittleEndian, vnetHdr)
+		vnetHdrBuf := vnetHdr.marshal()
 		builder.Add(vnetHdrBuf)
 	}
 
@@ -503,7 +531,7 @@ func (e *endpoint) sendBatch(batchFD int, batch []*stack.PacketBuffer) (int, tcp
 					vnetHdr.gsoSize = pkt.GSOOptions.MSS
 				}
 			}
-			vnetHdrBuf = binary.Marshal(make([]byte, 0, virtioNetHdrSize), binary.LittleEndian, vnetHdr)
+			vnetHdrBuf = vnetHdr.marshal()
 		}
 
 		var builder iovec.Builder