II. SYSTEM DESIGN
A. Style Objectives and Risk Model
Our product is designed to fulfill three requirements. First, AirBag should effectively con?ne untrusted applications such that any damage they may have would be separated without affecting the local Redmi 1S Smartphone Snapdragon 400 Quad Core 4.7 Inch cellphone atmosphere. The difficulties for recognizing this objective come from the essential awareness design behind Android os, which indicates that any app is allowed to connect with other applications or system daemons operating in the cellphone (through built-in IPC mechanisms). In other terms, once a harmful app is set up, it has a extensive strike area to launch the strike. The existence of benefit escalation or ability flow weaknesses [37] further reduces the con?nement need.
Second, AirBag should accomplish safe and smooth consumer encounter throughout the life expectancy of untrusted applications, from their set up to removal. Speci?cally, from the user’s viewpoint, AirBag should prevent running into extra pressure on customers. Correspondingly, the task to fulfill this objective is to transparently instantiate AirBag’s app solitude playback when an untrusted app is being set up and easily modify different playback surroundings when the untrusted app is being released or ended.
Third, because AirBag is implemented in resource-constrained cellular phones, it should remain light and convenient and present little efficiency expense. Moreover, AirBag should be generically convenient to a range of cellular phones without depending on special components or functions (that may be limited to certain Lenovo P780 cellphone models).
Threat Design and Program Supposition We believe the following attacker model while developing AirBag: Users will obtain and set up third-party untrusted applications. These applications may make an effort to manipulate weaknesses, especially those in blessed system daemons such as Zygote. By doing so, they could cause loss by either getting illegal accessibility various resources or destroying certain Redmi 1S cellphone features in a way not allowed by the customer or not known to the customer.
Meanwhile, we believe a reliable Lenovo P780 smart phone OS kernel, such as our light and convenient OS expansion to back up separated namespace and virtualized resources. As a client-side remedy, AirBag depends on this assumption to set up necessary reliable processing platform (TCB). Also, such assumption is distributed by other OS-level virtualization research initiatives [43], [19]. With that, we consider the threat of corrupting OS popcorn kernels drops outside the opportunity of this work.
B. Allowing Techniques
In Figure 1, we show the summary of AirBag to con?ne untrusted applications and its comparison with traditional Androidbased systems. The con?nement is mainly obtained from three key techniques: decoupled app solitude playback (AIR), namespace/?lesystem solitude, and context-aware system virtualization.
1) Decoupled App Isolation Runtime (AIR): Due to the awareness style of Android os, all applications discuss the same Android os playback and consequently any app is allowed to connect with other applications on the Redmi 1S cellphone. As said before, from the protection viewpoint, this reveals a extensive strike area. In AirBag, to reduce the strike area and prevent affecting the unique Android os playback, we select to decouple the untrusted app efficiency from it. A individual app solitude playback that allows applications to run on it and has (almost) no connections with the unique Android os playback is instantiated for untrusted app efficiency.
There are several bene?ts behind such a design: First, by offering a regular Android os subjective part that will be invoked by third-party Android os applications, AIR effectively guarantees proper efficiency of untrusted applications without affecting the unique Android os playback. Second, by design, AIR does not need to be reliable as it might be possibly affected by untrusted applications. Third, a individual app solitude playback also allows for personalization to back up different operating ways (Section II-C). This is necessary as AIR mainly includes essential Android os structure sessions and other assistance daemons that are assigned to manage various Lenovo P780 cellphone resources (e.g., system ID) or functions (e.g., sensors). Consequently, they likely accessibility personal or delicate details that could be of concern when being revealed to untrusted applications.
2) Namespace/Filesystem Isolation: With a individual Android os playback to variety untrusted applications, AirBag also provides a different namespace and ?lesystem to further limit and separate the abilities of procedures operating within. Because of namespace and ?lesystem solitude, an untrusted app within AirBag is not able to “see” and communicate with other procedures (e.g., genuine applications and system daemons) operating outside. Actually, all procedures operating within have their own view of operating PIDs, which is completely different from exterior procedures. Moreover, to proactively contain possible loss, AirBag has its own ?lesystem different from the regular system. For storage ef?ciency, we substantially make use of unionfs [48] to write AirBag’s ?lesystem and separate modi?cations from untrusted applications.
To intricate, when an Android os product is packed, a variety of assistance procedures or daemons (e.g., vold, folder and servicemanager) are created. Inside AirBag, we in the same way launch the same part of procedures but team them in their own cgroup [24]. By doing so, they are avoided from monitoring and getting procedures in another team (i.e., procedures in the unique local Android os system). The cgroup idea significantly helps AirBag management. Speci?cally, the set of procedures within AirBag is typically revoked until one untrusted app is being set up or released. The recently set up untrusted app will instantly become a member of this cgroup. Consequently, we can easily hold the whole cgroup when no untrusted app is effective to reduce the impact or reduce the efficiency and power consumption. Observe that cgroup is offered by the OS kernel and is believed to be reliable.
3) Context-Aware Device Virtualization: The existence of a individual AIR and namespace in AirBag unavoidably makes contentions for actual resources, even though AirBag delineates a border and by standard disallows any connections from within to outside and the other way around. To take care of the argument, there is a need to multiplex various resources. In our design, we develop a light and convenient OS-level expansion to mediate and multiplex the accesses from local and AirBag runtimes.
As an example, assume two applications need to upgrade the display at the same time. Typically, a single assistance daemon SurfaceFlinger is in charge of synthesizing details from different resources (including these two apps) and producing the ?nal outcome to be provided on the product display. However, with AirBag, these two applications run in two different runtimes and they will not discuss the same SurfaceFlinger assistance. Instead, AirBag has its own SurfaceFlinger assistance which will individually upgrade the display.
Our remedy is to virtualize components gadgets in a contextaware manner. Speci?cally, our light and convenient OS expansion contributes necessary multiplexing and demultiplexing systems in place when the actual components gadgets are being utilized. Also, our expansion keeps track of the current “active” Android os playback (or namespace) and always allows the effective playback to accessibility the components resources. Observe that an Android os playback is effective if an app on it keeps the focus, i.e., the customer is currently getting the app. To maintain the same consumer encounter, we stop an customer to at the same time communicate with two applications in different runtimes. Consequently, in any particular moment, you can find at most one effective playback. Meanwhile, to beautifully handle controversial accessibility from non-active playback, we take different strategies platform on the characteristics of appropriate components resources. For example, for touch-screen and control buttons, any press/release event will always be sent to the effective playback only. For display upgrade, as the framebuffer system car owner works real DMA functions from a storage area to the LCD operator components, we accordingly prepare two individual storage sections such that each atmosphere can individually provide different outcome without interfering each other. The framebuffer car owner can then select the effective storage area to perform DMA and thus have an real accessibility the LCD operator components.
C. Additional Capabilities
Beside the above key methods, we also developed extra abilities to accomplish the con?nement and improve consumer encounter.
1) Incognito/Pro?ling Modes: The decoupled AIR to variety untrusted applications offer unique possibilities for its personalization. Speci?cally, to prevent personal details disclosure, we present the anonymement method that basically equipment the AIR to remove any delicate details such as IMEI variety, Redmi 1S contact variety, and connections. For example, the device’s IMEI variety can be normally recovered by applications through the solutions offered by the Android os structure. When coming into the anonymement method, such solutions are con?gured to return photoshopped IMEI variety to the contacting app. Therefore, the separated app transparently continues with bogus details without extra threats. Also, AirBag makes a individual main ?lesystem that allows for convenient “restore to default” to reverse loss from untrusted applications. Moreover, we also offer pro?ling method that basically records the efficiency track of untrusted applications. The track is mainly gathered in terms of Android-speci?c logcat, which changes out to be very helpful for viruses research (Section IV).
2) User Con?rmation for Sensitive Operations: The decoupled AIR also provides exciting possibilities to further limit the abilities of separated applications. For example, a harmful app may make an effort to stealthily send SMS sms information to certain premium-rate numbers or record your Lenovo P780 Smartphone Android 4.2 5.0 Inch cellphone discussion. When such an app operates within AirBag, the accessibility related cellphone functions (e.g., stereo, audio, and camera) will instantly induce customer interest for acceptance. In other terms, the stealthy actions from these applications will now be taken to customer interest and the customer also has the choice to stop it. It is exciting to see that the latest Android os launch, i.e., Jellybean 4.2, presents a built-in protection function called top quality SMS con?rmation [2] to prevent viruses to holder up cellphone bills. While accomplishing similar goals, AirBag is different in reducing the accessibility certain cellphone functions outside the AIR atmosphere, thus offering more powerful sturdiness than any within solutions (as the inner built-in function can be possibly affected by untrusted applications for circumvention).
3) Seamless Integration: To accomplish smooth consumer encounter, AirBag presents little customer connections when an app is being set up or released. Speci?cally, when an untrusted app is being set up (or sideloaded), AirBag will immediate customer with a (default) choice to set up it within AirBag. If selected, AirBag basically noti?es its own PackageInstaller to start the set up. Observe that for an app downloadable from Internet, the Android os DownloadManager will store it in a speci?c listing located in microSD. In our model, we select to trade this listing read-only to AirBag so that its PackageInstaller can accessibility it for set up. For enhanced consumer encounter, AirBag will be set up as the standard PackageInstaller. Inside AirBag, we have a daemon that pays attention to the control from it to punch off inner app set up. In other terms, the separated applications are actually set up in the AirBag instead of the unique Android os playback. Moreover, for any app being set up within AirBag, AirBag will instantly create an app stub that keeps the same symbol from the unique app. (To indicate the point that it is actually within AirBag, we will connect a secure sign to the symbol.) When the app stub is invoked, AirBag will be noti?ed to easily launch the real app such that the customer would feel just like invoking a regular app (without recognizing the truth it is actually operating within AirBag). By doing so, the AIR becomes effective and the unique Android os playback goes to non-active. Once the customer selects to cancel the app, the unique Android os playback is started again back to effective.
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