Joanna Rutkowska- Security Challenges in Virtualized Environments

8/3/2019 Joanna Rutkowska- Security Challenges in Virtualized Environments

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Security Challenges in

Virtualized Environments

Joanna Rutkowska,Invisible Things Lab

RSA Conference,San Francisco, April 8th 2008


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Virtualization-based MALWARE

Using Virtual Machines for ISOLATION

NESTED virtualization

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Virtualization-basedMALWARE


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AMD-V

Intel VTx


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NO HOOKS!Cannot be detected usingany integrity scanner

On the fly installationNo boot/BIOS/etcmodifications necessary

No I/O virtualizationNegligible performanceimpact (your brand new 3Dcard will still work!)


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Blue Pill detection

Detecting a VMM Detecting

virtualization based

malware


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VMM detection

Directtimingana

lysis

BlueC

hicke

n

CPUspecificbehavior

TLBprofiling

Guesttimevirtualization

HPETtimers


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VMM detection?

Everything is going to be virtualized! Thus the information that there is ahypervisor in the system...

...would be pretty much useless...


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No Hooks!

Search for code Detect activity

(e.g. network packets)

Stealth by Design concept Covert channels

Wont workNested Page Tables(hardware SPT)

By PatternHeuristics

SimpleObfuscation

0day malwareMassive malware


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But why we cant use obfuscation for classic malware?

Because it leaves hooks anyways!And we can always find those hooks, no matter how

obfuscated the classic malware is!


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The whole big deal about Blue Pill is:NO HOOKS in the system!


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Disable virtualization?


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Install a trustedhypervisor first?


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Installing trusted

hypervisor

Static Root of Trust

Measurement

Dynamic Root of Trust

Measurement

BIOS > MBR > VMM

e.g. MS Bitlocker

SENTER (Intel TXT)

SKINIT (AMD SVM)


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SRTM and DRTM only assures that whatwe load is trusted...

...at the moment ofloading!

3 sec later... it could be exploited and get

compromised!


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Trusted != Secure (e.g. flawless)


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E.g. #1: The famous DMA problem


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Some

driver

Some

deviceI/O: asks the

device to

setup a DMA

transfer

Read/Write

memory access!


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IOMMU

Solution to the problem of DMA attacks

Intel calls it: VT-d Not much PC hardware supports it yet

Expected to change soon

No THIN HYPERVISORS without IOMMU!


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Other problems with VMMs?Stay tuned...


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All in all: its not trivial to have a trusted & secure

hypervisor installed...

... but for sure this is the proper way to go...


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Using Virtual Machines for ISOLATION


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3


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Using Virtual Machinesfor ISOLATION


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Originally ISOLATION was supposed to be provided byOperating Systems...

Separate processes/address spaces, User accounts & ACLs...


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But in practice current OSes simplyfail at providing isolation!


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Kernel bugs!

Kernel bugs!! Kernel bugs!!!

Bad design, e.g.:

XP and all runs as admin assumption

Vistas UAC assumes admin rights shouldbe granted to every installer program!


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Challenges

Performance

Why is VMM/hypervisor going to be moresecure then OSs kernel?


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VMM bugs?


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VMM Bugs

Bugs in hypervisors Bugs in additional

infrastructure


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E.g. #1: CVE-2007-4496

VMWare ESX 3.0.1 http://www.vmware.com/support/vi3/doc/esx-8258730-patch.html

Found by Rafal Wojtczuk (McAfee)

September 2007

Guest OS can cause memory corruptionon the host and potentiallyallow for

arbitrary code execution on the host
http://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.html


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E.g. #2: CVE-2007-0948

Microsoft Virtual Server 2005 R2

http://www.microsoft.com/technet/security/bulletin/ms07-049.mspx

Found by Rafal Wojtczuk (McAfee)

August 2007

Heap-based buffer overflow allows guest OSto execute arbitrary code on the host OS
http://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.htmlhttp://www.vmware.com/support/vi3/doc/esx-8258730-patch.html


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E.g. #3: CVE-2007-4993

Xen 3.0.3 http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1068

Found by Joris van Rantwijk

September 2007

By crafting a grub.conf file, the root user ina guest domain can trigger execution of

arbitrary Python code in domain 0.
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1068http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1068http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1068


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E.g. #4: Various Bugs

Paper by Tavis Ormandy (Google) http://taviso.decsystem.org/virtsec.pdf

April 2007 Disclosed bugs in VMWare, XEN, Bochs,

Virtual PC, Prallels

A simple fuzzers for: Instruction parsing by VMMs

I/O device emulation by VMMs
http://taviso.decsystem.org/virtsec.pdfhttp://taviso.decsystem.org/virtsec.pdf


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As you see current VMMs are far from being flawless...


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To make VMMs more secure we need to keep them

ultra-thin and small!


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Phoenix HyperSpace


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HyperCore:the type I hypervisor used for HyperSpace


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The HyperCore

Targets desktop/laptop systems

Guest OS execute at near-nativeperformance (including fancy graphics)

Support for full ACPI (Power Management)

Integrity: loaded via SecureCore BIOS

(Static Root of Trust Measurement)

Very thin - easy to audit!


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Speeding things up

Pass through for most devices SPT: 1-1 mapping for most pages for the

Primary OS


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Power Management

ACPI tables exposed to the Primary OS, so

that the overall power performance isoptimized

Efficient intercepts for power managementcontrol


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Integrity

Static RTM via Phoenixs SecureCore BIOS Dynamic RTM via Intels TXT/AMDs SKINIT

SMM-based watchdog for HyperCore code


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NESTED virtualization3


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What if auser wantsto run e.g.

Virtual PChere?


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Idea of how to handle this situation...


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Now, lets look at the actual details :)


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Lets start with AMD-V...


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?


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?


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RAX


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Looks convincing but wont work with more complexhypervisors...


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Nested Hypervisor

Nested Guest

Hypervisor


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Hypervisors expect to have GIF=1 whenVMEXIT occurs...

They might not be prepared to handle

interrupts just after VMEXIT from guests!

... but when we resume the nestedhypervisor CPU sets GIF=1, because we do

this via VMRUN, not VMEXIT...

Gettin aro nd the


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Getting around the

GIF Problem We need to emulate that GIF is 0 for the

nested hypervisor

We stop this emulation when: The nested hypervisor executes STGI

The nested hypervisor executes VMRUN

How do we emulate it?


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GIF0 emulation

VMCB1.V_INTR_MASKING = 1 Hosts RFLAGS.IF = 0 Intercept NMI, SMI, INIT, #DB and held (i.e. record

and reinject) or discard until we stop theemulation


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Additional details

Need to also intercept VMLOAD/VMSAVE

Need to virtualize VM_HSAVE_PA

ASID conflicts


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Conflicting ASIDs!


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But we can always reassign the ASID in the VMCB primthat we use to run the nested guest.


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Performance Impact

One additional #VMEXIT on every#VMEXIT that would occur in a non-

nested scenario

One additional #VMEXIT when the nestedhypervisor executes: STGI, CLGI,

VMLOAD, VMSAVE

Lots of space for optimization though


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http://bluepillproject.org
http://bluepillproject.org/http://bluepillproject.org/


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How AMD could help?

AMD could add an additional field to VMCB:EmulateGif0ForGuest

Additionally: virtualize STGI and CLGI whenthe above field is set to improve

performance Seems simple to do: just a few additional

lines in the microcode... :)


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Further thinking...

Virtualizing DEV for the nested hypervisorthat makes use of DEV?

Virtualizing IOMMU for the IOMMU-awarenested hypervisor?

Virtualizing Nested Paging mechanism forthe NP-aware nested hypervisor?


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How about Intel VT-x?


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Nested virtualization on VT-x

No GIF bit - no need to emulate GIF0 forthe nested hypervisor :)

No Tagged TLB - No ASID conflicts :) However:

VMX instructions can take memory operands -need to use complex operand parser

No tagged TLB - potentially bigger performanceimpact


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Nested VT-x: Status

We pretty much have that working already Code is messy and should be rewritten

e.g. the operand parser


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What Intel could do?

Extend info provided by:VMCS.VMX_INSTRUCTION_INFO

So that we dont need to parse memory

operand manually

Tagged TLB for better performance Other optimization?


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Who else does Nested (hardware-based) Virtualization?

IBM z/VM hypervisor on


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IBM z/VM hypervisor on

IBM System z mainframeRunning z/VM in a virtual

machine (that is, z/VM as a

guest of z/VM, also known

as second-level z/VM) isfunctionally supported but

is intended only for testing

purposes for the second-

level z/VM system and its

guests (called third-level

guests).

-- http://www.vm.ibm.com/pubs/

hcsf8b22.pdfIBM System z10, source: ibm.com
http://www.vm.ibm.com/pubs/hcsf8b22.pdfhttp://www.vm.ibm.com/pubs/hcsf8b22.pdfhttp://www.vm.ibm.com/pubs/hcsf8b22.pdfhttp://www.vm.ibm.com/pubs/hcsf8b22.pdfhttp://www.vm.ibm.com/pubs/hcsf8b22.pdf


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Confusion

AMD Nested Page Tables != Nested Virtualization!

NPT is a hardware alternative to Shadow PageTables (a good thing, BTW)

NPT is also called: Rapid Virtualization Indexing


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Solution: ensure hypervisor integrity via SRTM or DRTM


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SRTM/

DRTM

SRTM/DRTM do not protect the already loadedhypervisor, from being exploited if it is buggy!


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Keep hypervisors very slim!Do not put drivers there!


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Nested Virtualization:Useful Applications


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What if auser wantsto run e.g.

Virtual PChere?


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Phoenix Technologies has supported the research onnested hypervisors since Fall 2007


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Summary


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Virtualization technology could be used toimprove security on desktop systems

However there are non-trivial challenges inmaking this all working well...

... and not to introduce security problemsinstead...

Virtualization is cool ;)


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Invisible Things Labhttp://invisiblethingslab.com
http://invisiblethingslab.com/http://invisiblethingslab.com/

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Joanna Rutkowska- Security Challenges in Virtualized Environments