The smartphone market has grown explosively in recent years, as more and more consumers are attracted to the sensor-studded multipurpose devices. Android is particularly ascendant; as an open platform, smartphone manufacturers are free to extend and modify it, allowing them to differentiate themselves from their competitors. However, vendor customizations will inherently impact overall Android security and such impact is still largely unknown.In this paper, we analyze ten representative stock Android images from five popular smartphone vendors (with two models from each vendor). Our goal is to assess the extent of security issues that may be introduced from vendor customizations and further determine how the situation is evolving over time. In particular, we take a three-stage process: First, given a smartphone's stock image, we perform provenance analysis to classify each app in the image into three categories: apps originating from the AOSP, apps customized or written by the vendor, and third-party apps that are simply bundled into the stock image. Such provenance analysis allows for proper attribution of detected security issues in the examined Android images. Second, we analyze permission usages of pre-loaded apps to identify overprivileged ones that unnecessarily request more Android permissions than they actually use. Finally, in vulnerability analysis, we detect buggy pre-loaded apps that can be exploited to mount permission re-delegation attacks or leak private information.Our evaluation results are worrisome: vendor customizations are significant on stock Android devices and on the whole responsible for the bulk of the security problems we detected in each device. Specifically, our results show that on average 85.78% of all preloaded apps in examined stock images are overprivileged with a majority of them directly from vendor customizations. In addition, 64.71% to 85.00% of vulnerabilities we detected in examined images from every vendor (except for Sony) arose from vendor customizations. In general, this pattern held over time -newer smartphones, we found, are not necessarily more secure than older ones.

Hosted hypervisors (e.g., KVM) are being widely deployed. One key reason is that they can effectively take advantage of the mature features and broad user bases of commodity operating systems. However, they are not immune to exploitable software bugs. Particularly, due to the close integration with the host and the unique presence underneath guest virtual machines, a hosted hypervisor -if compromised -can also jeopardize the host system and completely take over all guests in the same physical machine.In this paper, we present HyperLock, a systematic approach to strictly isolate privileged, but potentially vulnerable, hosted hypervisors from compromising the host OSs. Specifically, we provide a secure hypervisor isolation runtime with its own separated address space and a restricted instruction set for safe execution. In addition, we propose another technique, i.e., hypervisor shadowing, to efficiently create a separate shadow hypervisor and pair it with each guest so that a compromised hypervisor can affect only the paired guest, not others. We have built a proof-ofconcept HyperLock prototype to confine the popular KVM hypervisor on Linux. Our results show that HyperLock has a much smaller (12%) trusted computing base (TCB) than the original KVM. Moreover, our system completely removes QEMU, the companion user program of KVM (with > 531K SLOC), from the TCB. The security experiments and performance measurements also demonstrated the practicality and effectiveness of our approach.

Abstract-Recent years have experienced explosive growth of smartphone sales. Inevitably, the rise in the popularity of smartphones also makes them an attractive target for attacks. In light of these threats, current mobile platform providers have developed various server-side vetting processes to block malicious applications ("apps"). While helpful, they are still far from ideal in achieving their goals. To make matters worse, the presence of alternative (less-regulated) mobile marketplaces also opens up new attack vectors, which necessitate client-side solutions (e.g., mobile anti-virus software) to run on mobile devices. However, existing client-side solutions still exhibit limitations in their capability or deployability.In this paper, we present AirBag, a lightweight OS-level virtualization approach to enhance the popular Android platform and boost our defense capability against mobile malware infection. Assuming a trusted smartphone OS kernel and the fact that untrusted apps will be eventually installed onto users' phones, AirBag is designed to isolate and prevent them from infecting our normal systems (e.g., corrupting the phone firmware) or stealthily leaking private information. More specifically, by dynamically creating an isolated runtime environment with its own dedicated namespace and virtualized system resources, AirBag not only allows for transparent execution of untrusted apps, but also effectively mediates their access to various system resources or phone functionalities (e.g., SMSs or phone calls). We have implemented a proof-of-concept prototype on three representative mobile devices, i.e., Google Nexus One, Nexus 7, and Samsung Galaxy S III. The evaluation results with a number of untrusted apps, including real-world mobile malware, demonstrate its practicality and effectiveness.

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