Virtual Machine Introspection to Detect and ProtectTamas K. Lengyeltklengyel@sec.in.tum.detamas.lengyel@zentific.comhttps://github.com/tklengyel

Agenda

1. Motivation & Cloud security

2. Xen

3. Virtual Machine Introspection

I. Isolation

II. Interpretation

III. Interposition

4. Demo

5. Public release of new tools

Motivation

This is my PhD topic

● Malware collection & analysis

DARPA Cyber Fast Track

● Cloud IDS/IPS prototype

Up-and-coming field

Cloud Security?

● Virtualization is a magic box of invulnerability

● Why bother if Cloud instances are short-lived and easily wiped?

● Isn't worth the cost of overhead

● It's not going to happen to me

● I'll just use my existing tools and be fine

Wrong!

Cloud Security

● In-guest AV / HIDS

✗ No isolation● Network IDS

✗ Limited or no context● Scan VM disk and memory

✗ No interposition

Better than nothing

Cloud Security!

● Move protection out from the VM

✔ Hypervisor based isolation● Full view of the VM state

✔ Interpret virtual hardware to see processes, users, connections, files..

● Actively monitor & control

✔ Interposition

Xen

Bare-metal VMM

Runs in VMX root

Minimal interface

Everything else is a domain, with one being special (dom0)

Isolation

We could move the security stack to dom0..

.. or move it into its own domain!

Xen allows for advanced disaggregation and role delegation

With some caveats..

Access control in Xen

Xen Security Modules (XSM)

– Disabled by default.

– Only usable starting with 4.3

In the guest kernel!

– if (!xen_initial_domain())

return -EPERM;

– We patched that in Linux 3.8

In XenStore (ignore for now)

– Domain meta info is only a plus

Access control in Xen

Security is no longer part of the TCB

Can be 1:1, 1:many or many:many

Designed for multi-tenant cloud deployments

Security doesn't mean the same thing for everyone

Interpretation

Interpreting the guest virtual hardware

– Memory– VCPU

Memory interpretation:

– Paging, paging, paging

OS interpretation:

– Debug symbols!

LibVMI + Rekall

LibVMI

– Xen and KVM support– Paging support for

● x86, x86+PAE, x86_64 & ARM– OS support

● Windows, Linux

Rekall

– Generates nice debug profiles– ..and lots of other fancy stuff

Finding Windows

Volatility: brute-force search

● “KDBG” scan● Easily hidden + lots of false positives

LibVMI + Rekall: use hardware info!

● VCPU0 FS/GS register → KPCR● KPCR – relative offset = Windows!● It is binding, malware can't touch it

Understanding Windows

Volatility: use the in-memory KDBG struct.

– Can be tampered with

– Heavily encoded in Windows 8 64-bit

LibVMI + Rekall: use the pre-generated debug profiles!

– Works with Windows 8 64-bit as well

– Different attacker model

Interposition

Scanning VM memory gets you a lot

– Volatility's pooltag scans

But it's not bulletproof and introduces TOCTOU issues

Interposition: induce & trap VMEXITs

Forward to security domain

Interposition

Intel to the rescue:CPUID, GETSEC, INVD, XSETBV, INVEPT, INVVPID, VMCALL, VMCLEAR, VMLAUNCH, VMPTRLD, VMPTRST, VMRESUME, VMXOFF, VMXON

And optionally:

CLTS, HLT, IN, INS/INSB/INSW/INSD, OUT, INVLPG, INVPCID, LGDT, LIDT, LLDT, LTR, SGDT, SIDT, SLDT, STR, LMSW, MONITOR, MOV from CR3, MOV from CR8, MOV to CR0, MOV to CR3, MOV to CR4, MOV to CR8, MOV DR, MWAIT, INT3, INT0, MTF ….

See the full list in Intel SDM 3c 25.1.3

Interposition with LibVMI

● MOV-TO-CR0/3/4– New process being scheduled, CPU feature

enabled/disabled, TLB flush, etc.

● EPT violation– Trap R/W/X of any memory page in the guest

– Invisible to the guest

– Needs to be reset after hit

● Singlestepping– Intel Monitor Trap Flag (MTF)

● Debug events (INT3)

Demo time!

http://goo.gl/XMSJ7y

DKOM no more!

It's still on the heap!

Demo time!

http://goo.gl/XMSJ7y

DRAKVUF

“Scalability, Fidelity and Stealth in the DRAKVUF Dynamic Malware Analysis System” - ACSAC 2014

http://drakvuf.com

Anyone gets the name reference?

Conclusion

● Cloud security requires new tools and new approaches

● VMI is rapidly maturing to fill the gap

● Dealing with rootkits is easier externally

● Tools are open-source (GPL/LGPL)

● Patches are welcome ;)

What's ahead

VMI gets you a lot.. but there are blind-spots

– Virt-DMA, emulation..● Who watches the watcher?

– SMM/AMT based VMM integrity check● Xen on ARM

– “Cloud” security for your phone/car!

Shout-out

Cheers to the Zentific crew

– Steve, Matt & Russ

To the Volatility crew

– MHL, Andrew, Gleeda & Moyix

To the Rekall crew

– Scudette

To Mudge

– Thanks for the CFT!

Thanks!