This presentation will detail a practical approach to memory introspection of virtual machines running on the Xen hypervisor with no in-guest footprint. The functionality makes use of the mem-event API with a number of improvements which enable the proper tracking of guest OS activity. The technology created on top of this Xen API opens the door for several immediate applications, including: rootkit detection and prevention, detection and action on several categories of malware, and event source information for low-level post-event forensics and correlation based on real event data during events.

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8/25/2014• 1Zero-Footprint Guest Memory Introspection from Xen
Xen Project DEVELOPER SUMMITAugust 18th, 2014Mihai DONȚU –Technical Project Manager, BitdefenderRavi SAHITA –Principal Engineer, IntelImproving VM Introspection Using Hardware Virtualization Extensions

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Outline
•Security issues
•Memory introspection
oOperation
oEvolution
•XenAccess and mem-events enhancements
•Sample usages
•Hardware Acceleration for memory introspection
•Conclusions

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Securityissues we are facing today
•Advanced malware types
oRootkits
oKernel exploits
oZero-days
•APTs, botnets, cyber-espionage and so on heavily rely on those…

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Securityissues we are facing today2

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Securityissuesweare facing today3
Malware today execute in the same context and with the same privileges as anti-malware software lack of isolation problem
Common Malware
Advanced Malware
Drivers
App1(Office)
OS Kernel
ISOLATIONKernel Controlled
App2(Browser)
SecuritySolution
SecurityFilter
Drivers
App1(Office)
OS Kernel
App2(Browser)
SecuritySolution
SecurityFilter
ISOLATIONKernel Controlled
Isolation Bypassed & Malware Controlled

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Conclusion: advanced attacks evade traditional security solutions

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Envision the big picture
so… what’s the big difference?...
Xen Hypervisor
dom0
SVA
(domU0)
domU1
MemoryIntrospection Engine
domU2
domUN
Protected area

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Memory introspection
Envision the big picture
Xen Hypervisor
dom0
SVA
(domU0)
domU1
MemoryIntrospection Engine
domU2
domUN
Protected area
Hypervisor Controlled, Hardware EnforcedSTRONG ISOLATION
Introspection Engine Alternative 2
Introspection Engine Alternative 3

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•Address a number of security issues from outside the guest OS without relying on functionality that can be rendered unreliable by advanced malware
•Analyze raw memory image of guest OS, services and user mode applications, then identify
okernel memory areas
odriver objects, driver code, IDT, etc.
ouser memory areas
oprocess code, process stack, process heap, etc.
What is memory introspection?
Envision the big picture

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•Use existent hardware virtualization extensions (Intel EPT / AMD RVI)
•Set hooks on guest OS memory
omark 4K pages as non-execute or non-writable
ohooking & notification must be supported efficientlyby HV & CPU
•Audit access of those areas by the code running in VM (OS or apps)
owrite attempts (driver objects, fast I/O tables, page tables)
oexecution attempts
•Allow or deny attempts –decision provided by security logic
How does it work?
Memory introspection

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How does it work? 2
Memory introspection
EPT protected areas
provide detection for various OS level changes (ex. new module load, new process start, …)
EPT protected areas
provide detection for attempts & protection against integrity violation
Guest VM PhysicalMemory Space
OS kernel code
kernel driver code and data
kernel data SSDT, IDT, …
user mode code
user mode stacks & heaps

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•Building a reliable image of the guest OS state
owhat objects are inside a guest VM?
owhat operations are being performed inside a guest VM?
oobject and event identification and correlation is done by the introspection engine –to decide event and object maliciousness
•Using hooks we can detect numerous events, including
oa driver / kernel module is loaded or unloaded
oa new user process or thread is created
ouser stack / heap is allocated
omemory is being paged in / out
How does it work? 3
Memory introspection

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How does it work? 4
Memory introspection
Traditional in-guest security solution
Out-of-guest memory introspection
OS Kernel
Typical Anti-Malware Kernel Module
Read mem by Virtual Addr, read files, registry, …
Enum processes, files, …
0101010011
MZ…
Setup well-knowncallbacks & notifications
New process PID 0x1234
HKLM...
XEN Hypervisor
Memory Introspection Engine
Read mem by Physical AddrRead vCPUregisters
0101010011
Setup EPT hooks on mempages (by Physical Addr)
Write / Execute attempt on PA 0x000A12345678
RAX = 0x1234RIP = 0x7890

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•bridging the semantic gap –obtain rich semantics from only raw physical memory pages and virtual CPU registers
ohow do we correlate 4K memory pages with semantically rich and meaningful OS specific data structures?
oto be solved by security solution vendors
•forward lots of mem-event notifications with low overhead to introspection engine
oto be solved by hypervisor and CPU vendors
Two big challenges
Memory introspection

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Memory introspection evolution
•2003 –Garfinkel & Rosenblum: “A Virtual Machine Introspection Based Architecture for Intrusion Detection”
othe starting point for a considerable amount of academic research
•2006 –Jiang & Wang: “’Out-of-the-box’ Monitoring of VM-based High-Interaction Honeypots”
•2008 –Dinaburg et al.: “Ether: Malware Analysis via Hardware Virtualization Extensions”
oBuilt on top of Xen 3.1
•2008 –VMsafe API announced by VMware, which provides access to a guest’s:
oCPU, memory, disk, I/O devices etc.
osupported memory introspection for vSphere / ESXi
•2010 –VMware vShield Endpoint(as a replacement for VMsafe API)
oin-guest agent based
ofile introspection only
•2012 –VMware deprecates VMsafe

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Memory introspection in Xen
•2007 –XenAccess, XenProbes
•2008 –Lares
•2009 –first patches for the mem-events API
•2010 –LibVMI –uses XenAccess and XenStore
otargets Xen, but support for other HV-s can be added
oinsufficient flexibility in changing page permissions
ono support for mapping guest memory RW
oinsufficient information about the guest CPUs
ohigh overhead when reading the vCPUregister state
oa ‘complete’ initialization requires intimate knowledge about the guest OS
ocode for handling specific guest OS-s (Windows, with Linux in the works)

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XenAccess and mem-events enhancements
•2014 –Bitdefender published a set of patches (as RFC) to enhance the mem-events API
oimplements its own version of LibVMI
osimpler API
onothing [guest] OS specific
osupport for other HV-s can be added
oallows to map guest memory (via EPT)
ouses a very simple page cache to optimize (un)maps
ooptimized access to specific resources
•Some patches went into mainline, others will follow shortly

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XenAccess and mem-events enhancements2
mem-event notification
Xen Hypervisor
SVA
(domU0)
MemoryIntrospection Engine
domU1
uint32_t flags;
uint32_t vcpu_id;
uint64_t gfn;
…
mem_event_regs_t regs;

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Example use of the extended API
Xen Hypervisor
dom0
SVA
(domU0)
MemoryIntrospection Engine
Protected areas
Critical Kernel Module
Critical Kernel Module
App1
App2
…
Code, stacks, heaps, IAT, …
Code, stacks, heaps, IAT, …
Code, stacks, heaps, IAT, …
Mem-events andVMCALLs facilitated by XEN

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Example use of the extended API 2
•Bitdefender’s own introspection engine can
oprotect the kernel from known rootkit hooking techniques
oprotect user processes (e.g. browsers, MS Office, Adobe Reader, …) from
ocode injection
ofunction detouring
ocode execution from stack / heap
ounpacked malicious code
oinject remediation tools into the guest on-the-fly (no help from ‘within’ needed)
•Runs in userspace in a user domain (SVA –Security Virtual Appliance)
•Introspection logic has very small overhead
obulk of the overhead is given by sending / receiving events and calls between protected guest VMs and SVA

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Hardware Acceleration for Memory IntrospectionRavi SahitaIntel

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Hardware Acceleration for Memory Introspection
Factors Limiting VM Memory Monitoring Performance
Addressing Lack of Memory Isolation
Addressing Performance gaps for execution and data access-control policies
Xen Extensions

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Factors Limiting VM Memory Monitoring Performance
Round-trip time
–Monitoring execution and data accesses
–Dynamic data structures imply high frequency events
Filtering events
–Monitoring data accesses requires filtering non- interesting events due to 4K page sharing
Further, round-trip time is amplified with VMMs nesting

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Multiple EPTs as Protection Domains
CPU0
Hypervisor
Intel®VT-xwith EPT
VM0
Extended Page Table(EPT) Domains
EPTWalker
Execution crossing
EPT domains or data
Accesses causing events
host physical address
Intel®Virtualization Technology for IA-32, Intel®64 and Intel®Architecture (Intel®VT-x)
OS kernel
Code/data
(RX/RW)
Driver
Code (RX)
Driver
Code (RO)
OS kernel
Code/data
(RO/NP)
Data
(RW)
Data
(NP)

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Addressing Lack of Isolation…
Xen
EPT Domains
EPT Domains
policy
events
CPU
Hypervisor- derived isolation

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Kernel module
Kernel module
Security module
…Without Sacrificing Performance
Must allow for legal execution of components isolated in permission domains
Each execution transfer across domains leads to VM exits that the hypervisor must mediate
As components isolated via domains, numerous execution transfers are induced
High Frequency of such VM exits to the hypervisor causes overhead
Process
Hypervisor
Eliminate these induced VM exitson legalcontrol transfers
Legal control transfers

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VM Functions: Hypercalls Without VM Exits
VM Functions: Intel®VT-x extensions for services configured by the hypervisor
–Different VM Functions correspond to different services
Hypervisor configures VM Functions via new fields in VMCS
Guest software invokes VM Functions via new instruction (VMFUNC<leaf>)
–Value in EAX specifies which VM Function leaf is invoked
CPU provides services as configured with no VM exit
Intel®Virtualization Technology for IA-32, Intel®64 and Intel®Architecture (Intel®VT-x)

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VMFUNC-based Domain Switching
Paravirtualized software can request protection domain switch via VMFUNC (specifying domain index)
Hypervisor pre- configures domain index to EPTPs
Hypervisor pre- configures domain boundaries
View switching to speed up access control policies
CPU0
Hypervisor
Intel®VT-xwith EPT
VM0
Extended Page Table(EPT) domains
EPTWalker
VMFUNC (EPTP switch)
Host physical address
Aternate ExtendedPage Table(EPT) list
Intel®Virtualization Technology for IA-32, Intel®64 and Intel®Architecture (Intel®VT-x)

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Asynchronous Induced VMExits
In VM-introspection scenarios critical data is monitored in place
Legacy approaches are to VMExit and emulate access
Alternatively, VMExit and switch views to single step the guest (MTF)
High frequency of writes to monitored data cause high overhead
Requires custom logic in the VMM increasing complexity/state in the hypervisor
Kernel (Guest)
Hypervisor
EPT Domains
Ring-0
Monitoring
Agent
Monitored
Memory
WRITE
2. EPT-V
VMexit
3. VMResume to single step access
Single
Step Memory
View
4. VMexit after access completed
Access Policy
1. View Policies
5. VMResume
EPT Domains
Emulation

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Accelerating Induced Events
Via Virtualization Exception (#VE)
–Mutates EPT violations into a new IA exception–delivered through guest IDT
VMM enables EPT violation conversion to #VE
Data access monitoring view policies setup in EPT domains
Data access causes #VE instead of VMexit
Guest monitoring agent can emulate in guest OR use VMFUNC to single step access
Hypervisor (VMX-root)
Kernel/VMX-non-root
EPT Domains
Monitoring
Service
Monitored
Memory
1. Handle #VE
3. Complete single step or emulate in guest
Single Step
Memory
View
2. Setup single step or emulate
WRITE
Access Policy
1. Policies
VMFUNC
VMFUNC
#VE
#VE info
VMFUNC
EPT Domains

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VMFUNC Configuration
Hypervisor checks IA32_VMX_VMFUNC MSR for allowed VM-Function controls
Opts-in by setting “Enable VM functions” in the secondary processor-based VM- execution controls field
Activates “EPTP switching” by setting bit-0 in the VM Function Control
Configure alternate EPTP values in memory referenced via VMCS field
Guest software uses VMFUNC opcode with leaf selector EAX=0 and ECX containing the index of EPTP (view) selected
Errors reported to the hypervisor via VM Exits
“Enable VM functions” VM- execution control (bit 13)
EPTP-list address
0:Alternate-EPTP
1:Alternate-EPTP
511:Alternate-EPTP
“EPTP switching” (bit 0)
Secondary processor-based VM-execution controls
VMFunction Control (new)
In memory
VMCS
In VMCS
(new)
IA32_VMX_VMFUNC MSR (index 491H)

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Virtualization Exception (VE) Configuration
Enumerated by the VMM via capability MSR
Set VMCS “Enable VE” bit
Negotiate “VE Info” page with Hypervisor
#VE delivered through guest IDT
Suppress VE EPTE Bit 63
–Set on pages the VMM does not want to cause a #VE for
“Enable VE” VM-execution control (bit 18)
VE Information Address
Exit Reason
Suppress
Exit Qualification
Secondary processor-based VM-execution controls
In memory
Virtual Machine Control Structure (VMCS)
In VMCS
(new)
IA32_VMX_PROCBASED_ CTLS2 (48Bh) Bit 50
Guest Linear Address
Guest Physical Address
EPTP Index

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Xen Extensions
1.Efficiently creating and maintaining alternate EPT views/domains via extension of p2m
2.Hypercalls to edit EPT permissions without conflicting with Xen EPT management
3.Report guest-specific memory events via #VE in a Xen compatible manner (Suppress #VE EPTE bit)
4.Enabling CPU acceleration if VMFUNC and #VE CPU enumerated and opted-in
Xen Hypervisor
domUN
domU0
Security
Engine
EPT Domains
EPT Domains
Security
Engine
CPU
#VE
EPT Domains
EPT Domains
#VE

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VM Introspection Performance Improvements
Round-trip time
–VMFUNC to allow safe, fast Memory View (EPT) switches
–VMexits mutated to #VE for guest memory monitoring
Filtering events
–Reduced latency of #VE event handling reduces overhead of filtering events
Round-trip time amplification due to VMM nesting
–No VMexits to root VMM implies no amplification of VMexits due to EPT violations
Scalable Runtime Memory Introspection w/o VT overheads

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•Today Xen can be the base for providing a much improved layer of security –serves as a model for other HV vendors
oTruly agentless security (zero in guest footprint)
oIT Admins can deploy introspection based solutions seamlessly, without changing a single line of config inside the guest VMs
•Hardware enforced isolation (against kernel exploits, zero days, …)
•Hardware extensions enable intra-VM isolation to enable protected agent based introspection for high frequency access monitoring and agent isolation
•Both models require straight-forward Xen infrastructure changes (multi-EPT views, hardware acceleration capabilities)
Conclusions

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Thank you!
enterprise.bitdefender.com