CSE543 - Computer and Network Security Module:...

CSE543 - Introduction to Computer and Network Security Page

CSE543 - Computer and Network Security

Module: Virtualization

Professor Trent Jaeger

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CSE543 - Computer and Network Security Page

Operating System Quandary• Q: What is the primary goal of system security?• OS enables multiple users/programs to share resources

on a physical device‣ OS’s now have millions of lines of code

‣ Access control policies of OS become complex• E.g., SELinux

• What can we say about security?

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Virtual Machines• Instead of using system software

to control sharing, use system software to enable isolation

• Virtualization‣ “a technique for hiding the physical

characteristics of computing resources from the way in which others systems, applications, and end users interact with those resources”

• Virtual Machines‣ Single physical resource can

appear as multiple logical resources

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Virtualization Architectures• Full system simulation (QEMU)

‣ CPU can be simulated

• Paravirtualization (Xen) ‣ VM has a special API

‣ Requires OS changes

• Native virtualization (VMware) ‣ Simulate enough HW to run OS

‣ OS is for same CPU

• Application virtualization (JVM) ‣ Application API

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Virtual Machine Types• Type I

‣ Lowest layer of software is VMM

‣ E.g., Xen, VAX VMM, etc.

• Type II ‣ Runs on a host operating system

‣ E.g., VMWare, JVM, etc.

• Q: What are the trust model issues with Type II compared to Type I?

5Penn State Systems and Internet Infrastructure Security Lab Page

Virtual Machine Monitor Approaches

Hardware!

Host OS!

VMM!

Guest OS 1! Guest OS 2!

App! App!

Hardware!

Host OS! VMM!


App! App!

Hardware!

VMM!


App! App!

Type 2 VMM! Type 1 VMM!Hybrid VMM!

JVM!CLR!

VMware Workstation!

MS Virtual Server!KVM!

VMware ESX!Xen!

MS Hyper-V!


How Can VMs Improve Security?• Isolation

‣ Separate two applications to run in two VMs

• Specialize‣ Run a hardened, specialized kernel for some applications

• Isolate groups of VMs‣ Like a VLAN

• Better IDS from outside the VM‣ VM Introspection

• Control data release to VMs‣ TCB can decide whether to release data to a new VM

• And more...

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What is Virtualized• What do you need to do to virtualize a system?• All sensitive instructions must be privileged‣ Sensitive: May impact security of VMs‣ Privileged: Must run in privileged domain (ring 0)

• VMs must still be able to use devices‣ Must be able to use host’s hardware devices despite

not being the “host’s” operating system‣ Without compromising the VMM

• Must control access to virtualized resources‣ Different granularity than typical OS access control

• Subjects: VMs; Objects: Disk volumes

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VAX VMM Security Kernel• A1 assured system that enforces MLS (circa 1991)

‣ Based on an assured virtual machine monitor (VMM)• AKA hypervisor

‣ Lessons from VAX/SVS for High-Assurance VM Systems, IEEE S&P Magazine, 2012

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Ultrix OS VMS OS

VMM Security Kernel

VMS OS

Applications(Top Secret)

Applications(Secret)

Applications(Unclassified)

MemoryDevice

DiskDevice

PrintDevice

DisplayDevice ...


VAX VMM Security Kernel• A1 assured virtual machine system• Virtualization‣ Provide isolation

• Sensitive instructions must be virtualized (i.e., require privilege)

• Access to sensitive data must be virtualized (ditto)

‣ MLS• Mandatory protection of VMs, volumes

‣ I/O Processing• Paravirtualization - modify OSes to call VMM• Special driver interface (all in VMM security kernel)

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Modern Virtualization• Modern Hardware‣ Native Virtualization Support‣ IOMMU

• Modern Hypervisors‣ Xen is 300K+ LOC‣ MAC enforcement in VMMs

• NetTop, sHype, Xen Security Modules

• Modern Assurance‣ Some advances, but small (seL4)‣ 10K LOC is max that has been assured

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Native Virtualization• What does virtualization hardware do?• Self-virtualization‣ All sensitive instructions are now privileged

• Device I/O‣ Paravirtualization improvements ‣ Direct device assignment (using IOMMU for

protection)

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IOMMU• Memory Management Unit for I/O• What does a tradition MMU do?• What does an IOMMU do?

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MAC for Modern VMMs• Xen, VMware, etc. provide ‣ Isolation and I/O: sensitive instructions are made

privileged‣ What about enforcing flexible MAC policies?

• This is something that VAXVMM did...

13Penn State Systems and Internet Infrastructure Security Lab Page

IOMMU Role In System

Application!

Application!

System !Software!

RAM!

Peripheral!

Peripheral!

Peripheral!

Application!

MMU!

IOM

MU!

control


Xen• Originally, Paravirtualized Hypervisor• Privileged VM

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VM: DomU VM: DomU

Xen Hypervisor

Guest OS’ Guest OS’

Partitioned Resources

DeviceRequestsDom 0

Host OS’Drivers

VM Services


MAC for Modern VMMs• Xen, VMware, etc. provide ‣ Isolation and I/O: sensitive instructions are made

privileged‣ What about enforcing flexible MAC policies?

• VAXVMM could do that…

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NetTop• Isolated networks of VMs• Alternative to “air gap” security

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VM: Secret VM: Public

SELinux Host OS


VMWareMLS

VM: Secret VM: Public

SELinux Host OS


VMWareMLS


Xen sHype• Controlled information flows among VMs

‣ Subjects (VMs) and Objects (VMs - via network)

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VM: DomU VM: DomU

Xen Hypervisor


Partitioned Resources

DeviceRequestsDom 0

Host OS’Drivers

VM Services

Ref Mon


Intrusion Detection w/ VMs• Can virtualization help in detecting an intrusion?

• Network intrusion detection‣ Can only track packets to and from host

‣ Cannot see what is running on the host

• Host intrusion detection‣ Can see processes on host

‣ But adversary can see HIDS too!

‣ Stuxnet took advantage of that

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Intrusion Detection w/ VMs• Garfinkel and Rosenblum paper (NDSS 2003)• Premise: Use VMM to enable introspection of one

VM from another‣ For antivirus or host intrusion detection

• Leverages 3 properties of VMM‣ Isolation: protect from target‣ Inspection: can see target’s memory‣ Interposition: can intercept privileged instructions

• Can then “checkpoint” target VM‣ What is the checkpoint algorithm in terms of above 3?

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Intrusion Detection w/ VMs

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Policy Framework

MetadataGuest OS

OS Interface Library

Guest OS

Guest Apps

Virtual Machine

Virtual Machine Monitor

callback orResponse

Policy Modules

Query Response

Hardware State

Config File

Policy Engine

IDS

Monitored Host

Command

Figure 1. A High-Level View of our VMI-Based IDS Architecture: On the right is the virtual machine (VM) thatruns the host being monitored. On the left is the VMI-based IDS with its major components: the OS interfacelibrary that provides an OS-level view of the VM by interpreting the hardware state exported by the VMM, the policyengine consisting of a common framework for building policies, and policy modules that implement specific intrusiondetection policies. The virtual machine monitor provides a substrate that isolates the IDS from the monitored VM andallows the IDS to inspect the state of the VM. The VMM also allows the IDS to interpose on interactions between theguest OS/guest applications and the virtual hardware.

INSPECTION COMMANDS are used to directly examineVM state such as memory and register contents, and I/Odevices’ flags.MONITOR COMMANDS are used to sense when certain

machine events occur and request notification through anevent delivery mechanism. For example, it is possible fora VMI to get notified when a certain range of memorychanges, a privileged register changes, or a device statechange occurs (e.g. Ethernet interface address is changed).ADMINISTRATIVE COMMANDS allow the VMI IDS to

control the execution of a VM. This interface allows theVMI IDS to suspend a VM’s execution, resume a sus-pended VM, checkpoint the VM, and reboot the VM.These commands are primarily useful for bootstrappingthe system and for automating response to a compromise.A VMI IDS is only given administrative control over theVM that it is monitoring.The VMM can reply to commands synchronously

(e.g. when the value of a register is queried) or asyn-chronously (e.g. to notify the VMI IDS that there has beena change to a portion of memory).

4.3 The VMI IDS

The VMI IDS is responsible for implementing intrusiondetection policies by analyzing machine state and ma-

chine events through the VMM interface. The VMI IDSis divided into two parts, the OS interface library and thepolicy engine. The OS interface library’s job is to providean OS-level view of the virtual machine’s state in orderto facilitate easy policy development and implementation.The policy engine’s job is purely to execute IDS policiesby using the OS interface library and the VMM interface.

4.3.1 The OS Interface Library

VMMs manage state strictly at the hardware level, butprefer to reason about intrusion detection in terms of OS-level semantics. Consider a situation where we want todetect tampering with our sshd process by periodicallyperforming integrity checks on its code segment. A VMMcan provide us access to any page of physical memory ordisk block in a virtual machine, but discovering the con-tents of sshd’s code segment requires answering queriesabout machine state in the context of the OS running inthe VM: “where in virtual memory does sshd’s code seg-ment reside?”, “what part of the code segment is in mem-ory?”, and “what part is out on disk?”We need to provide some means of interpreting low-

level machine state from the VMM in terms of the higher-level OS structures. We would like to write the code todo this once and provide a common interface to it, instead


Introspection Challenges• Can you find what you are looking for?

‣ OS’s are complex and have important dynamic data• Lots of function pointers (data, but not really dynamic)

‣ Semantic gap gets larger when you want to inspect apps

• Can you monitor everything you need to?‣ Need to mediate at critical times

‣ Use privileged commands, hardware watchpoints, debuggers, or voluntary hooks (like paravirtualization)

‣ Too many interrupts impedes performance

• Can you protect yourself from adversary?‣ Adversary could try to compromise IDS from VM

‣ Adversary could try to compromise VMM from VM or IDS

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Virtual Machine Threats• How does the insertion of a virtual machine layer

change the threats against the system?

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Virtual Machine Rootkit• Rootkit

‣ Malicious software installed by an attacker on a system

‣ Enable it to run on each boot

• OS Rootkits‣ Kernel module, signal handler, ...

‣ When the kernel is booted, the module is installed and intercepts user process requests, interrupts, etc.

‣ E.g., keylogger

• VM Rootkit‣ Research project from Michigan and Microsoft

‣ If security service runs in VM, then a rootkit in VMM can evade security

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Java Virtual Machine• Interpret Java bytecodes

‣ Machine specification defined by bytecode

‣ On all architectures, run same bytecodes• Write once, run anywhere

• Can run multiple programs w/i JVM simultaneously‣ Different ‘classloaders’ can result in different protection

domains

• How do we enforce access control?

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Java Security Architecture• Java 1.0: Applets and Applications• Java 1.1: Signed code (trusted remote -- think

Authenticode)

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Java Security Architecture

• Java 1.2: Flexible access control, included in Java 2

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Stack Inspection• Authorize based on protection domains on the stack

‣ Intersection of permissions all sources• All must have permission

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Do Privileged• doPrivileged terminates backtrace • Like setuid, with similar risks

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Take Away• VM systems focus on isolation between VMs

‣ Useful for coarse-grained security

• VM systems sometimes provide MAC to allow controlled interaction‣ Same kind of policies as for OS, coarse-grained objects (VMs)

• Can use for VM introspection‣ Watch out for VMM rootkits...

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