VMM Based Rootkit Detection on Android
Class PresentationPete Bohman, Adam Kunk, Erik Shaw
Problem Statement
• Rootkit detection and prevention on the Android platform with specific regards to the sensitive resources Android provides.• Kapersky 2011: 1046 unique malware strains
targeting mobile platforms• Android platform built on Linux Kernel, a well known
target.• Sensitive information on smart phones• GPS, contacts, text messages, call log
Defensive Rootkit Approaches• User mode rootkits
– Process infection, binary patching, lib hooks
• User mode integrity checkers– tripwire, chkrootkit, rkthunter, AV scanner
• Kernel mode rootkits– malicious device drivers and lkms– sys call hooking, kernel data structure manipulation
• Kernel level inspection– behavioral analysis, data structure integrity checkers, hook detection
• But… Any kernel level inspection mechanisms can be subverted by kernel level rootkits
Our Approach• Two Pronged• VMM inspection • Ensures integrity of static kernel module• Isolated from host OS
• Kernel module security mechanisms • System call integrity checks• Hidden process detection• Android capability table
• We exercise a “layer-below” level of security in which we establish trust beneath the kernel
Solution PreviewAndroid Software Stack
Android VMM ensures integrity of static kernel module
Kernel module implements security mechanisms
Overview
• Design• VMM Design• Protected KM Design• Implementation• Results• Demo Presentation• Conclusion• Q&A
VMM Interface Design
Android VMM
Hardware (Emulator)
Linux Kernel
Trusted KM <ISR>
Libraries and Runtime
Application Framework
1. Hardware Timer Interrupt
2. Validate Protected KM 3. Raise Monitor Interrupt
4. Invoke KM
Protection KM Design
Linux KernelTrusted KMSystem Call WhitelistOriginal Sys Call Table
Libraries and Runtime
Maps
Application Framework
Contacts SMS Phone
Content Provider
Location Provider
Activity Manager
Open
Malicious Native
ApplicationSystem Calls
Open SocketRead GPSSQL Query
Malicious LKM
SysCall Table
Implementation
• Instead of utilizing a VMM as the lowest layer, we created a new hardware device in the QEMU emulator• Hardware device based on virtualized timer which
expires at predefined intervals• When a timer interval expires, an interrupt is
generated and the timer is reset• During each interrupt, the hardware device calls into
our kernel module to pass execution• Integrity checks are done on the sys_call_table
Implementation (cont.)
• We implemented a static Kernel Module (KM) in order to make integrity checks on the sys_call_table• The kernel module contains a copy of the original
sys_call_table and compares this to the running version
• The KM also sets its own hooks in the sys_call_table in order to detect malicious access to sensitive resources• e.g. Check for invalid process access to sys_open system call
attempting to open a sensitive resource file (contacts2.db)
Results
• We are able to detect/correct modifications to the sys_call_table• We are able to prevent malicious access to sensitive
resources• TODO Mention Malicious App and LKM
• TODO: (Insert link to demo)
Conclusion
• Layer Below Protection• Security of the Linux kernel must be rooted in a layer
below the kernel• Code contained solely in the kernel is subject to any
kernel-level attack
• Sensitive Resource Protection• Android mobile phones contain lots of sensitive
information that must be protected
App PermissionsDalvik VM IsolationApp signatures
Limits application abilities in order to prevent malicious behavior.
Virus ScannersRemote Lockout
Modified system binariesTrojan’d servicesStolen device
Linux user and group permissions
Access control
Architecture Layer Security Mechanism Threat Mitigation
Linux Kernel Source with
Protection KMCompilation
Kernel Image
Protected Text Sect.
Protected Data Sect.
QEMU Emulator(VMM) Compilation
QEMU Emulator(VMM)Protected TextProtected Data
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