Creating and configuring Virtual Machines for your project

With REVEN v2, you can build RE projects where analyzed scenarios are recorded from Virtual Machines(VMs), either VirtualBox or QEMU. Although choosing one vs the other will depend on your work habits, we recommand:

  • Using VirtualBox when:

    • VM configuration and setup is a heavy job.
    • Some specific hardware must be studied.

  • Using QEMU in all other cases to experience replay high fidelity.

    IMPORTANT NOTE: replayers do NOT support VMs with too much RAM (strictly more than 3072MB for QEMU and 2048MB for Vbox). DO NOT record scenarios with more than these limits of RAM or the replay will fail.

Records can be started from VM snapshots. The Project Manager allows some control over those snapshots. Here are some keys to understand what's happening.

Introducing VM snapshots

Both QEMU and VirtualBox VMs use two kinds of snapshots:

  • Disk snapshots: contain no more than the content of the machine local filesystem. Restoring a disk snapshot brings you to the VM boot, which might not be convenient when recording a scenario.
  • Live snapshots: contain the full saved state of a running VM, including the RAM, CPU state, and filesystem. Restoring a live snapshot brings you to the exact VM running state where you took it.

NOTE: in case of modifications in the VM hardware parameters, a live snapshot will probably become unrecoverable.

Please refer to the dedicated VirtualBox and QEMU pages for more information on how to work with each system's snapshots.

Disk snapshot statuses

Disk snapshots can have the following statuses in the Project Manager, relating to OSSI availability:

: Prepared, means the OS Specific Information (OSSI) has been extracted from the snapshot, namely the filesystem content and kernel information.

: Inherited, means the snapshot "inherits" the OSSI of a parent snapshot. NOTE: If the current snapshot contains new binaries compared to its parent snapshot, OSSI may not be available for these binaries in the Analysis stage. Should you need this OSSI, launch a Prepare operation on the current snapshot.

: Not prepared, means no Prepare operation has occured for this snapshot. Therefore, no OSSI is available for this snapshot. Without OSSI, binary and symbol names will not be available in the Analysis stage.

Optimizing the VM system for analysis

In order to optimize scenario recording and replay performance, you will need to remove system features that are not useful to your scenarios.

As REVEN will record the entire system execution, the following VM system configuration steps will optimize the virtual machine characteristics and scenario recordings:

  1. Limit the virtual machine RAM to reduce disk footprint.
  2. Disable any non essential system features so as to reduce noise in the scenario recording, hence the replay duration, the trace size and complexity, which makes analysis easier and faster.

Microsoft Windows system preparation

On Windows systems, the following preparation steps are required to improve REVEN performance and to make all its features fully operational.

  • Disable desktop graphical effects.
  • Disable unnecessary services.
  • Disable KPTI protections (required to get OS Specific Information (OSSI) such as symbol names).
  • Disable the CompactOS option (required for performance and to get OSSI).

Disabling unnecessary services

Regarding Windows 10 VMs, the REVEN package comes with a sample Powershell script designed to lighten a Windows 10 system, so as to greatly improve its performance and reduce the size of REVEN traces. This script is available from the Downloads page of the Project Manager.

IMPORTANT: Please note that this script is provided to REVEN's users as-is, without any guarantee, as a convenient tool. Therefore, it must be considered for what it is - an example. It is strongly recommended to backup any VM before running the script on it. Besides, the script may require modifications to fit your specific configurations. For example, non-English VMs may require some translation in the script, such as administrator to administrateur in a French VM.

Before using the script, apply the following configuration:

  • Disable Windows Defender and optionally the firewall:
    • As an Administrator, launch gpedit.msc.
    • Navigate to "Local Computer Policy\Computer Configuration\Administrative Templates\Windows Components\Windows Defender\Turn off Windows Defender" and set the Enabled radio button.
    • Navigate to "Local Computer Policy\Computer Configuration\Windows Settings\Security Settings\Windows Firewall with Advanced Security" and set it to Off.

On Windows 10, in an administrator Powershell console, you can:

  • Get help about the script's capabilities and usage:
> Get-Help windows10_lightener.ps1
  • Run the script to disable a maximum of services:
> Set-ExecutionPolicy Unrestricted
(confirm)
> windows10_lightener.ps1 -All

IMPORTANT: AV disablement by this script is not persistent after a VM reboot, which is is why we recommended disabling it via groups policies above. Alternatively, the script may be executed after each reboot to disable the AV services again:

> Set-ExecutionPolicy Unrestricted
(confirm)
> windows10_lightener.ps1 -DisableAV

Manually disable the following services:

  • Print spooler
  • DPS
  • Themes
  • Workstation (SMB protocol)

In order to enable networking, reactivate the following services:

  • Windows Event Log

  • Network Connections

  • Network List Service

  • Run the script to disable basic services only:

> Set-ExecutionPolicy Unrestricted
(confirm)
> windows10_lightener.ps1 -Basic

Disabling the KPTI protections

KPTI (Kernel Page-Table Isolation) protections were introduced with the meltdown patches. If KPTI protections are enabled, OSSI will be available only on ring 0 or admin processes.

Microsoft provides the following steps to disable KPTI protections:

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 3 /f
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f
shutdown -r

Disabling the CompactOS Windows 10 option

On Windows 10, the CompactOS feature lets you run the operating system from compressed files to maintain a small footprint. However, this feature is not compatible with the Prepare stage of the REVEN workflow, which is required by the OSSI features.

Besides, uncompression routines may unnecessarily increase a scenario's trace size.

Therefore it is recommended to check the status of the Compact OS feature on a Windows 10 VM with the following command issued as the Administrator user:

> Compact.exe /CompactOS:query
The system is in the Compact state. It will remain in this state unless
an administrator changes it.
>

If the CompactOS feature is active, it is recommended to disable it:

> Compact.exe /CompactOS:never
Uncompressing OS binaries /
Completed uncompressing OS binaries.

15483 files within 11064 directories were uncompressed.
>

If necessary, it can be later re-enabled:

> Compact.exe /CompactOS:always
Completed Compressing OS binaries.

15483 files within 11064 directories were compressed.
4,454,521,157 total bytes of data are stored in 2,620,926,932 bytes.
The compression ratio is 1.7 to 1.
>

Linux systems optimizations

On Linux systems, common optimizations include:

  • Disabling Xorg server when not needed.
  • Disabling the console framebuffer if not needed. For example, on Debian systems, in file /etc/default/grub, add the line:
GRUB_TERMINAL=console
  • Disabling any unwanted background service.
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