hypervisor framework

79

Click here to load reader

Upload: edgar-barbosa

Post on 04-Jun-2015

1.858 views

Category:

Technology


3 download

DESCRIPTION

SyScan 2009 talk about hypervisors.

TRANSCRIPT

Page 1: Hypervisor Framework

Private & Confidential Property of COSEINC

Page 2: Hypervisor Framework

Who am I?

• Senior Security Researcher at COSEINC

• One of the developers of BluePill, a hardware-based virtualization rootkit.

• Creator of one of the most effective methods to detect virtualization rootkits.

• Experience with systems programming (kernel, device drivers) and reverse engineering for x86/x64 architectures.

Private & Confidential Property of COSEINC

Page 3: Hypervisor Framework

1. Review of the implementation methods for virtualization of the x86 architecture.

2. Show the complexity of using hardware supported virtualization instructions to implement virtual machines.

3. Present a framework that makes easy the task of creation of hypervisors.

4. Applications of the framework

5. Security aspects

Private & Confidential Property of COSEINC

Page 4: Hypervisor Framework

X86 VIRTUALIZATION The COSEINC Hypervisor Framework

Private & Confidential Property of COSEINC

Page 5: Hypervisor Framework

• System Virtual Machines: VM able to run multiple operating systems concurrently

• The code responsible for the virtualization is called (VMM).

• Provides isolation between the guest OS

• Physical hardware resources are shared between the multiple virtual machines

Private & Confidential Property of COSEINC

Page 6: Hypervisor Framework

IA-32 processor

VMM

Windows guest

Linux guest

1. Type I (native) The VMM runs directly on the host’s hardware.

Hardware resources controlled by the VMM. Examples: VMware ESX, Microsoft Hyper-V

Private & Confidential Property of COSEINC

Page 7: Hypervisor Framework

IA-32 processor

VMM

Windows guest

Linux guest

Operating System

• Type II – Hosted The VMM runs as an application. Hardware

resources controlled by the host OS. The COSEINC hypervisor framework creates a Type-II VMM.

Examples: VMware Workstation.

Private & Confidential Property of COSEINC

Page 8: Hypervisor Framework

• When the guest VM uses the same Instruction Set Architecture (ISA) of the host machine, the guest instructions can be executed in 2 ways:

– Emulation

– Direct native execution

Private & Confidential Property of COSEINC

Page 9: Hypervisor Framework

• The VMM must read and interpret each guest instruction

• Can be implemented using code interpretation or binary translation

• Performance penalty

Private & Confidential Property of COSEINC

Page 10: Hypervisor Framework

• The guest instructions are executed directly on the CPU.

• Great performance.

• Some instructions still need to be emulated.

• How to decide which instructions can be used for direct native execution?

Private & Confidential Property of COSEINC

Page 11: Hypervisor Framework

• Popek and Goldberg published a paper which formally defines the requirements of an ISA for the implementation of virtual machines.

• The VMMs must have 3 properties:

– 1. Equivalence

– 2. Resource control

– 3. Efficiency

Private & Confidential Property of COSEINC

Page 12: Hypervisor Framework

• Basically all the VMM detection methods are based on violations of the Equivalence property.

Private & Confidential Property of COSEINC

Page 13: Hypervisor Framework

• Violation: VMM bug exploitation.

Private & Confidential Property of COSEINC

Page 14: Hypervisor Framework

• Depends on the features of the host ISA.

• How to implement efficient virtual machines on the x86 architecture?

Private & Confidential Property of COSEINC

Page 15: Hypervisor Framework

Private & Confidential Property of COSEINC

Page 16: Hypervisor Framework

• Innocuous instructions are instructions which doesn’t change or affect system configuration or resources.

• A efficient VMM allows the direct execution of innocuous instructions.

• Examples: – mov eax, 00204012h

– shr ebx, 03

– xor eax, eax

– cmp ebx, ecx

Private & Confidential Property of COSEINC

Page 17: Hypervisor Framework

• Sensitive instructions affect system resources or behavior

• The VMM must the direct execution of sensitive instructions!

• The IA-32 instruction set contains 17 sensitive instructions [2]

• Examples: – wrmsr – mov CR3, eax – out dx, eax

Private & Confidential Property of COSEINC

Page 18: Hypervisor Framework

• All the VMM need now is a way to intercept the execution of the sensitive instructions.

• This is easy when the sensitive instruction is privileged!

• A sensitive instruction is if it traps if the machine is executing in user mode and does not trap in system mode.

• In the x86 architecture, system mode = CPL zero (ring 0)

Private & Confidential Property of COSEINC

Page 19: Hypervisor Framework

INNOCUOUS INSTRUCTIONS

KERNEL code

cmp eax, ebx jnz 8c0dab00 xor edx, edx mov eax, 030h

wrmsr

cmp eax, 020Fh jnz 08000bc00 shr eax, 8

SENSITIVE INSTRUCTION

Private & Confidential Property of COSEINC

Page 20: Hypervisor Framework

Set CPL to RING 3 and execute the code directly on

the cpu

KERNEL code

cmp eax, ebx jnz 8c0dab00 xor edx, edx mov eax, 030h

wrmsr

cmp eax, 020Fh jnz 08000bc00 shr eax, 8

#GENERAL PROTECTION

FAULT

VMM trap handler routine

(emulation)

Private & Confidential Property of COSEINC

Page 21: Hypervisor Framework

• Virtualization of guest instruction would be very easy if all sensitive instructions generates a fault in ring 3.

• There are sensitive but non-privileged instructions in the x86 architecture!

• A sensitive non-privileged instruction will not generate an exception in ring 3!

Private & Confidential Property of COSEINC

Page 22: Hypervisor Framework

• POPFD instruction writes a DWORD value in the EFLAGS register.

• It’s a sensitive instruction because it can be used to set the IF flag.

• The IF (Interrupt Flag) controls the hardware external interrupt mechanism.

Private & Confidential Property of COSEINC

Page 23: Hypervisor Framework

• Problem: Executing POPFD in ring3 will not generate a fault! The CPU just ignores the IF flag modification attempt.

• How to virtualize sensitive non-privileged instructions?

Private & Confidential Property of COSEINC

Page 24: Hypervisor Framework

• How VMware Player VMM is able to prevent direct execution of non-privileged instructions?

• VMware Player is a Type II VMM

• The hypervisor is stored as a PE resource inside the vmware-vmx.exe executable.

• ELF executable loaded directly inside the Windows kernel memory by the vmx86.sys device driver

Private & Confidential Property of COSEINC

Page 25: Hypervisor Framework

vmplayer.exe

vmware-vmx.exe

USER MODE

KERNEL MODE

vmx86.sys

ntoskrnl.exe

Private & Confidential Property of COSEINC

Vmware Hypervisor

ELF executable stored as a PE resource

Page 26: Hypervisor Framework

• Solution: Scan all the guest code instructions and search for non-privileged instructions.

• Replace the non-privileged instructions by a privileged instruction.

• VMM handles the faults and emulates the execution of the non-privileded instruction.

Private & Confidential Property of COSEINC

Page 27: Hypervisor Framework

1. Review x86 virtualization implementation methods.

2. Show how to use the Intel VT® to implement virtual machines.

3. Present a framework to make easy the task of creation of hypervisors.

4. Applications of the framework

5. Security and detection discussion

Private & Confidential Property of COSEINC

Page 28: Hypervisor Framework

The COSEINC Hypervisor Framework

Private & Confidential Property of COSEINC

Page 29: Hypervisor Framework

• Virtualizable ISA

– If all sensitive instructions of some ISA are privileged, the processor is considered to be ‘virtualizable’[3]

• IA-32 is obviously not-virtualizable.

• New instruction sets created by Intel and AMD

– Intel Virtual Machine eXtensions (VMX)

– AMD Secure Virtual Machine (SVM)

Private & Confidential Property of COSEINC

Page 30: Hypervisor Framework

• Presentation focus on Intel VMX. AMD SVM concepts are very similar.

• New form of processor operation: the ‘VMX operation mode’

• VMX mode

– activated by the VMXON instruction.

Private & Confidential Property of COSEINC

Page 31: Hypervisor Framework

• VMXON fails if virtualization is locked.

• Locked by default in the BIOS for security reasons

• Ring -1.

• There’s no more need to move kernel guest code from ring 0 to ring 3. Guest kernel code can run directly in ring 0.

Private & Confidential Property of COSEINC

Page 32: Hypervisor Framework

• 2 types of VMX operation: – VMX root operation

– VMX non-root operation

• VMX root operation – New instructions available (VMX instructions)

– Used by the VMM (hypervisor)

• VMX non-root operation – Restricted mode of operation

– Certain instructions and events are intercepted to facilitate virtualization.

Private & Confidential Property of COSEINC

Page 33: Hypervisor Framework

• Transitions between VMX root operation and VMX non-root operation are called ‘VMX transitions’

• Transition from the VMM to the guest: VM-ENTRY.

• Transition from the Guest VM to the VMM: VMEXIT

Private & Confidential Property of COSEINC

Page 34: Hypervisor Framework

Hypervisor (vmx root operation)

VIRTUAL MACHINE

(vmx non-root operation)

VM-ENTRY – vmresume/vmlaunch

VM-EXIT event interception

Private & Confidential Property of COSEINC

Page 35: Hypervisor Framework

Creating a VMM with Intel VT® - first steps

• Detection of Intel VMX instruction support.

– CPUID

• Enable VMX (CR4)

– VMXE bit

• Check status of the Lock bit (rdmsr)

– More about in the security section

• Setup of the VMXON region

Private & Confidential Property of COSEINC

Page 36: Hypervisor Framework

Creating a VMM with Intel VT® - first steps

• Enable VMX instructions (VMXON)

• Create and configure the VMCS region of each guest VM.

• Launch the guest VM with VMLAUNCH instruction

• Wait for VM-exit events

Private & Confidential Property of COSEINC

Page 37: Hypervisor Framework

VMCS

• Virtual Machine Control Structure

• Most important vmx data structure

• One VMCS for each Virtual Machine and for each CPU core.

• It controls the behavior of VMX transitions

Private & Confidential Property of COSEINC

Page 38: Hypervisor Framework

VMCS

• VMM must not access the VMCS directly.

• Read and write access to the VMCS via VMREAD and VMWRITE instructions.

• Internal structure undocumented but reverse engineering it is easy.

Private & Confidential Property of COSEINC

Page 39: Hypervisor Framework

VMXON and VMCS areas VMXON region

CPU A

VM Linux

VM Windows

VMXON region CPU B

VMCS #1A

VMCS #2A

VMCS #1B

VMCS #2B

CPU A CPU B

Private & Confidential Property of COSEINC

Page 40: Hypervisor Framework

VMCS logical groups

Guest-state area

Host-state area

VM-execution control fields

VM-exit control fields

VM-entry control fields

VM-exit information fields

4K-aligned physical address

6 logical areas

Private & Confidential Property of COSEINC

Page 41: Hypervisor Framework

Guest-state area

• Area of the VMCS where guest context information is stored.

• On #VMEXIT, guest processor state is saved in this area.

• On VMENTRY this information is loaded. • Register state:

– Control Registers – Debug Registers – RSP, RIP, RFLAGS – LDTR, GDTR, IDTR – Segment selectors – Model Specific Registers

Private & Confidential Property of COSEINC

Page 42: Hypervisor Framework

Guest-state area

• Non-register state

– Activity State

– Interruptibility state

– VMCS link pointer

• For future expansions

Private & Confidential Property of COSEINC

Page 43: Hypervisor Framework

Host-state area

• Contains information about the host (VMM)

• Processor stated is loaded from this area after each #VMEXIT

• Registers:

– RIP (Entry-point address of the hypervisor routine responsible for handling #VMEXIT events)

– RSP, RFLAGS

– MSR

Private & Confidential Property of COSEINC

Page 44: Hypervisor Framework

VM-execution control fields

• Controls how the VM will be executed. • The instructions that the hypervisor wants to intercept are

specified in these control fields. – Example: HLT, INVLPG, MWAIT, RDPMC, RDTSC, MOV-DR

• Exception bitmap – Bitmap which controls interception of CPU interrupts like page

faults, debug exceptions, #GP, ...

• I/O bitmap – Can be used to control interception of I/O ports

• MSR bitmap – Interception of Model Specific Registers

• Some instructions wil unconditionally result in VMEXIT

Private & Confidential Property of COSEINC

Page 45: Hypervisor Framework

VM-entry control fields

• Controls the behavior of VM entries.

• Includes information about SMM, debug registers and some MSRs.

• Guest Event Injection:

– It’s possible to inject virtual interrupt or exception in the guest

– Types of interrupts allowed:

• External, NMI, Hardware exceptions, software interrupt.

Private & Confidential Property of COSEINC

Page 46: Hypervisor Framework

VM-exit fields

• `VM-exit control fields` which controls the behavior of VM exits.

• VM-exit information fields:

– Read-only fields with information about the most recent VM exit

– Exit reason

– Exit qualification

Private & Confidential Property of COSEINC

Page 47: Hypervisor Framework

Interception

• After configuring the VMCS, the hypervisor can launch the virtual machine and wait for a VMEXIT event.

• When a instruction is intercepted in the guest, the processor will: – Save the VM-exit reason information in the VMCS

– Save guest context information

– Load the host-state area

– Transfer control to the hypervisor

Private & Confidential Property of COSEINC

Page 48: Hypervisor Framework

VMX ROOT-MODE RING 0

VMM

#VMEXIT event handler

VMX NON-ROOT RING 0

mov eax, 23 inc edx

xor ebx, edx sub ecx

cmp eax, 1 jnz c080df00

retn

mov cr3, ebx #VMEXIT

VMLAUNCH

#VMRESUME

Private & Confidential Property of COSEINC

Page 49: Hypervisor Framework

1. Review x86 virtualization implementation methods.

2. Show how to use the Intel VT® to implement virtual machines.

3. Present a framework to make easy the task of creation of hypervisors.

4. Applications of the framework

5. Security and detection discussion

Private & Confidential Property of COSEINC

Page 50: Hypervisor Framework

• Creating a VMM using these new hardware virtualization ISA is complex – More complex features always comming: EPT for

nested paging

• Very hard to find and to fix bugs • No debugger • Intel VT error codes not very useful

– Code 33 = “VM-entry failure due to invalid guest state”

– What’s exactly invalid in the guest state? – More than 40 suspects!

Private & Confidential Property of COSEINC

Page 51: Hypervisor Framework

• The COSEINC Hypervisor Framework, referred from now as just the ‘framework’, enables you to easily create a Hosted Virtual Machine Monitor (Type II VMM) using the Windows Operating System.

• Simple and easy-to-use API exported

• Abstraction over the different hardware virtualization instruction sets (VMX-SVM)

Private & Confidential Property of COSEINC

Page 52: Hypervisor Framework

• 2 versions: – 32-bits Windows device driver

– 64-bits Windows device driver

• API exported methods: – Export table

– IOCTL codes for user-mode communication

• Initial version only for Windows, but porting to Mac/Linux should not be difficult.

• Release date: very soon!

Private & Confidential Property of COSEINC

Page 53: Hypervisor Framework

Features

• Automatic detection of the virtualization instruction sets.

• SMP support

• Evaluation of the lock bit

• Detailed error-status codes

• Plugin-like architecture

Private & Confidential Property of COSEINC

Page 54: Hypervisor Framework

Architecture

Framework

Ring 0 Operating System

Kernel

Ring -1

User applications Ring 3

Framework Client

Private & Confidential Property of COSEINC

Page 55: Hypervisor Framework

API

• The full documentation of the API will be released with the framework.

• Preliminary documentation. Subject to change.

• Function categories: – Virtual Machine management functions

• Creation and deletion of Virtual Machines.

• Executing and resuming a virtual machine.

– Interception Events functions • The framework call the registered client function callbacks.

– Root guest VM.

Private & Confidential Property of COSEINC

Page 56: Hypervisor Framework

Virtual Machine management

• VMSTATUS CreateVirtualMachine ( IN VMINFO *vminfo );

• This function creates a new virtual machine in the system.

• Fails if virtualization MSR is locked by the BIOS.

Private & Confidential Property of COSEINC

Page 57: Hypervisor Framework

VMINFO data structure

• Most important framework data structure

• Contains all the information needed to create and control a VM:

– all the GUEST context information

– GDT, LDT, Page Tables, Control Registers, ...

– Interception handler function callback address.

– Contains Event Injection information

– VMEXIT information

Private & Confidential Property of COSEINC

Page 58: Hypervisor Framework

GUEST_INFO

Registers

Segments

Descriptor Tables

Control

Debug

Model Specific

CONTROL_INFO

Interception

Event Injection

I/O

Interrupts

MSR

Virtual Machine

VMINFO data structure

VMEXIT info Extra info

Private & Confidential Property of COSEINC

Page 59: Hypervisor Framework

Interception Event management

• VMSTATUS VirtualMachineExec ( IN VMINFO *vminfo );

• This function controls the execution of the virtual machine. It can be called after the creation of the VM and to resume the execution of the VM after an intercept event.

• If the VMM must inject some event in the guest VM, the information is provided in the VMINFO data structure.

Private & Confidential Property of COSEINC

Page 60: Hypervisor Framework

x

VM creation and execution

Framework Client (VMM

plugin)

Framework

CreateVirtualMachine( )

Intercept event

handler

Intercept Event Message

VirtualMachineExec( )

VirtualMachineExec( )

Private & Confidential Property of COSEINC

VM

Page 61: Hypervisor Framework

VM Scheduler

VM message handler

Timer interrupt

VM Event Router

Virtual Machine

VM Event Manager

Hypervisor

Framework – Client communication

Page 62: Hypervisor Framework

Root guest VM

• One of the best features of the framework:

– Automatic conversion of the host operating system into a virtual machine in runtime!

• This guest VM is called ‘root VM’

• The creation of the root VM is optional and controlled by the api.

• Root VM is shared between all loaded plugins.

Private & Confidential Property of COSEINC

Page 63: Hypervisor Framework

1. Review x86 virtualization implementation methods.

2. Show how to use the Intel VT® to implement virtual machines.

3. Present a framework to make easy the task of creation of hypervisors.

4. Applications of the framework

5. Security and detection discussion

Private & Confidential Property of COSEINC

Page 64: Hypervisor Framework

The COSEINC Hypervisor Framework

Private & Confidential Property of COSEINC

Page 65: Hypervisor Framework

Applications of the framework

• Specially useful for education and research purposes

• Can abe used to create any type of small and fast VM. Not only system VMs.

• The best features are available when using the root guest VM.

Private & Confidential Property of COSEINC

Page 66: Hypervisor Framework

Process VM

• Whole virtualization of a process or a thread is possible with the framework.

• Normally achieved by interception of system calls.

• Additional functions will be added to the API for better memory virtualization.

• No support for EPT in the first version.

Private & Confidential Property of COSEINC

Page 67: Hypervisor Framework

Syscall hooking

• A great number of system monitoring and security tools are implemented using system call hooking methods.

• Old Windows OS uses INT 2eh

• Linux and newer Windows OS uses SYSENTER instructions

Private & Confidential Property of COSEINC

Page 68: Hypervisor Framework

Syscall mechanism - illustration

SYSENTER_EIP MSR

SYSENTER_CS MSR

mov edx, esp sysenter

mov ecx, 23h push 30h pop fs ...

nt!KiFastCallEntry

Ntdll.dll

Private & Confidential Property of COSEINC

Windows OS syscall mechanism

Page 69: Hypervisor Framework

Syscall hooking

• Syscall hooking methods includes:

– Patching syscall handler

– Patching of IDT table

– Patching the SYSENTER Model Specific registers

Private & Confidential Property of COSEINC

Page 70: Hypervisor Framework

Syscall interception

• Syscall interception using the root guest VM • No need to hook SSDT • No need to patch/modify guest kernel code • Virtualization of the SYSENTER MSR • Plugin (framework)

– VMINFO->ControlInfo->Interception->MSR

• Can also be applied to Linux guests • Virtualized IDTR for old guest operating systems

using INT xx instructions for syscall implementation.

Private & Confidential Property of COSEINC

Page 71: Hypervisor Framework

Instrumentation

• Instrumentation is also easy to implement using the Interruptibility controls in the VMCS.

• Performance registers are also virtualizable

• Tools:

– Optimization tools

– System statistics

Private & Confidential Property of COSEINC

Page 72: Hypervisor Framework

Nested virtualization

• The framework doesn’t provide support for nested virtualization

• But it is possible to add this feature via a VMM plugin.

• Also, a virtualization debugger could be implemented!

Private & Confidential Property of COSEINC

Page 73: Hypervisor Framework

1. Review x86 virtualization implementation methods.

2. Show how to use the Intel VT® to implement virtual machines.

3. Present a framework to make easy the task of creation of hypervisors.

4. Applications of the framework

5. Security and detection discussion

Private & Confidential Property of COSEINC

Page 74: Hypervisor Framework

64-bits

• The framework and the plugins must be digitally signed to run in 64-bit versions of Windows.

Private & Confidential Property of COSEINC

Page 75: Hypervisor Framework

• MSR IA32_FEATURE_CONTROL (Index 3Ah)

• Controls:

– SMX – Safer Mode eXtensions

• Disabled by default in the BIOS

Private & Confidential Property of COSEINC

Page 76: Hypervisor Framework

• “There is no software-visible bit whose setting indicates whether a logical processor is in VMX non-root operation. This fact may allow a VMM to prevent guest software from determining that it is running in a virtual machine.” – Intel manual 3 – 19.3

• VMX transitions are cpu-expensive operations.

• Thousand of cycles just for a simple VMEXIT.

• SyScan 2007 – Detecting BluePill

Private & Confidential Property of COSEINC

Page 77: Hypervisor Framework

QUESTIONS?

Page 78: Hypervisor Framework

THANK YOU FOR YOUR TIME!

Page 79: Hypervisor Framework

1. John Scott Robin and Cynthia E. Irvine (2000). "Analysis of the Intel Pentium's Ability to Support a Secure Virtual Machine Monitor". Proc. 9th USENIX Security Symposium.

2. Virtual Machines: Versatile Platforms for System and Processes – Jim Smith, Ravi Nair – Morgan Kaufmann - 2005

3. Intel manuals (www.intel.com)