When running a VM, Hard Disks should be opened ShareMode=0 to prevent other processes writing to them

[Mark Cranness]

While a VM is running, the Hard Disk file (VDI) is opened in a mode that allows shared read-write by other processes. The hard disk files should be opened in locked/exclusive write/no write sharing mode to ensure safe access.

e.g. In Windows, while a VM is running, the following test C code succesfully opens the VDI for writing (but should be blocked):

CreateFile(TEXT("Play.vdi")
  ,GENERIC_READ | GENERIC_WRITE
  ,FILE_SHARE_READ | FILE_SHARE_WRITE
  ,NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL)

Existing behaviour of allowing other processes write access allows another VM on a remote PC to boot a VDI on a network share, resulting in two VMs having concurrent access to the VDI which causes a BSOD. Instead an error message prevent starting of the second remote VM. See ​Windows XP Guest BSOD