Speaker 1: Have you ever peered beyond the apps and the sleek
Speaker 1: interface of your Android phone and wondered what truly makes
Speaker 1: it tick? Today, we're not just scratching the surface. We're
Speaker 1: taking a deep dive into Android's core internals.
Speaker 2: Yeah, getting into the nuts and bolts exactly.
Speaker 1: We're going straight to the source with insights from Jonathan
Speaker 1: Levin's Android Internals, a Confectioner's cookbook, Volume one. And this
Speaker 1: book it's written specifically for you, the power user, right.
Speaker 2: And what's truly fascinating about this source, I think is
Speaker 2: that it's not some dry technical manual just for developers,
Speaker 2: not at all. No, it's more of a conceptual journey.
Speaker 2: It's rich with illustrations, and it's really designed to give
Speaker 2: you a profound understanding without getting totally lost and lines
Speaker 2: and lines of code. Okay, So our mission here is
Speaker 2: to distill those essential nuggets of knowledge, basically offer you
Speaker 2: a shortcut to mastering the very foundations of well, the
Speaker 2: world's most popular operating system.
Speaker 1: And what a mission it is. So, whether you're maybe
Speaker 1: brushing up for a meeting, exploring a new field, or
Speaker 1: just driven by insatiable curiosity, prepare for some genuine aha
Speaker 1: moments will navigate Androids a unique design. It's sophisticated file system,
Speaker 1: the intricate boot process, and those silent services that keep
Speaker 1: it all running smoothly, always with its Linux foundations in mind.
Speaker 2: Of course, Absolutely, you're.
Speaker 1: About to gain a thorough understanding, hopefully without the information overload.
Speaker 2: Yeah, that's the plan.
Speaker 1: So to begin, let's consider the unique lens we're getting here.
Speaker 1: Jonathan Lovin, our author, He brings a remarkable journey to
Speaker 1: this book. We're talking Unix, Linux, Windows, OSX and deep
Speaker 1: into security, right, a broad background, and he recognized that
Speaker 1: understanding security is and I quote largely a projection of internals,
Speaker 1: which is well a profound insight when you think about it,
Speaker 1: it really is.
Speaker 2: It shapes how you look at security problems.
Speaker 1: He's tackled Apple's operating systems before, but this Android book
Speaker 1: it's his first self published work, and it's crafted specifically
Speaker 1: to give you the power user, this deeper conceptual understanding.
Speaker 1: It's a perspective rooted in like decades of hands on
Speaker 1: system analysis.
Speaker 2: That background is so crucial because it immediately helps us
Speaker 2: tackle a common misconception when people say Android is built
Speaker 2: on Linux. I mean, how true is that really question.
Speaker 2: Levin makes it super clear, it's not just another Linux distribution.
Speaker 1: Okay.
Speaker 2: Well, the kernel, the absolute core of the OS, it
Speaker 2: shares a lot with standard Linux, yes, But the user
Speaker 2: mode side, so everything above the kernel, that's where it
Speaker 2: diverges significantly. Well, we see two entirely new components that
Speaker 2: are pure androidisms, as he calls them. First the Delphic runtime,
Speaker 2: which has since evolved into art the Android runtime, and
Speaker 2: second the hardware distraction layer usually called the HL. It
Speaker 2: basically provides a uniform interface to all the different device
Speaker 2: hardware out there.
Speaker 1: Like a translator between the software and the specific chips exactly.
Speaker 2: And on top of that, Android uses a custom in
Speaker 2: it process, not the traditional Linux one, and the BIONICC
Speaker 2: library instead of the standard glib. These aren't just minor tweaks.
Speaker 1: All sounds fundamental they are.
Speaker 2: They're fundamental architectural choices that make Android distinct and uniquely
Speaker 2: optimized for the constraints of mobile devices. I think battery
Speaker 2: life memory limits.
Speaker 1: That distinction Linux foundation, but with its own unique, highly
Speaker 1: specialized architecture that's really key. It makes you wonder how
Speaker 1: did these early architectural choices shape androids incredibly rapid evolution.
Speaker 2: Yeah, it's been fast.
Speaker 1: I mean we've seen a dozen major versions, twenty one
Speaker 1: API levels in just what seven years since it started?
Speaker 1: From a power users standpoint? What were some of those
Speaker 1: pivotal system level changes that really made a difference?
Speaker 2: Okay, yeah, we connect this to Android's bigger story. Several
Speaker 2: versions definitely stand out. They introduce core innovations that fundamentally
Speaker 2: altered how Android worked and well how we interact with it.
Speaker 2: Which ones Let's start with Froyo twenty ten. This release
Speaker 2: wasn't just about giving users more space by letting them
Speaker 2: install apps on sd cards tho.
Speaker 1: That was big at the time, it.
Speaker 2: Was huge, but it was also a critical response to
Speaker 2: the exploding app ecosystem, and crucially, it introduced Android Secure
Speaker 2: Containers accacs.
Speaker 1: Yeah.
Speaker 2: I think of ATC as like a secure encrypted vault
Speaker 2: for those app files, especially when they're on typically less
Speaker 2: secure removable storage. It helped mitigate the new security risks
Speaker 2: that came with that flexibility.
Speaker 1: Ah, okay, makes sense. What came next?
Speaker 2: Then you have Jellybean around twenty twelve twenty thirteen. This
Speaker 2: brought multi user support, initially just for tablets, but it
Speaker 2: was a massive.
Speaker 1: Shift like different logins on one device, exactly.
Speaker 2: Separate user interfaces, isolated data just on a desktop. And
Speaker 2: for security, it also introduced selnicx to Android. That's a
Speaker 2: mandatory access control framework.
Speaker 1: Mandatory access control. How's that different from regular permissions?
Speaker 2: Well, unlike traditional Linux permissions which are kind of voluntary,
Speaker 2: selinicx proactively forces a really strict policy. It's like an
Speaker 2: omnipresent security guard, making sure every process only does exactly
Speaker 2: what it's explicitly allowed to do, no exceptions.
Speaker 1: Wow, okay, sounds strict.
Speaker 2: It is and very effective. Jellybean also closed a significant
Speaker 2: USB debugging hole by forcing authentication over ADB, another security.
Speaker 1: Plus good move. What about KitKat twenty thirteen?
Speaker 2: KitKat brought some really clever under the hood optimizations focus
Speaker 2: squarely on.
Speaker 1: Battery life, always important on mobile definitely.
Speaker 2: The implemented timer coalescing and sensor batching. These are intelligent
Speaker 2: strategies to basically group together multiple small system events or
Speaker 2: sensor readings into single, less frequent operations.
Speaker 1: So waking the phone up less.
Speaker 2: Often, precisely, instead of waking the system constantly for individual
Speaker 2: little updates. Yeah, it would collect them and process them
Speaker 2: all at once. Saved significant power Kitcat also introduced dm verity.
Speaker 2: Dm verity Yeah, it provides cryptographic integrity checking for the
Speaker 2: system partition. It's essentially a digital fingerprint that ensures the
Speaker 2: core operating system hasn't been tampered.
Speaker 1: With, So checking if the OS files are still the
Speaker 1: original trusted.
Speaker 2: Ones exactly a really important security feature, okay.
Speaker 1: And then Lollipop in twenty fourteen that felt like a huge.
Speaker 2: Overhaul, monumental visually, yes, it was material design, but internally
Speaker 2: the big news was it fully adopted the Android Run
Speaker 2: Time RT, replacing delvic correct and RT was a huge shift.
Speaker 2: It compiles application code ahead of time AOT, meaning meaning
Speaker 2: it translates the app's code into native machine instructions before
Speaker 2: the app even runs, usually during installation.
Speaker 1: Ah okay, not just in time like Delva right.
Speaker 2: This results in significantly faster application launch times and much
Speaker 2: smoother performance overall, especially when paired with its new sixty
Speaker 2: four bit architecture support. Lollipop also launched Project.
Speaker 1: Volta Volta Battery Improvements again.
Speaker 2: Yep, the whole set of improvements for better battery life,
Speaker 2: plus more detailed power monitoring tools so you can get
Speaker 2: more insight into what's draining your device useful.
Speaker 1: And finally, the M Preview in twenty fifteen, M, which.
Speaker 2: Became Marshmallow, built further on power management. It introduced dose mode.
Speaker 1: Dose.
Speaker 2: Yeah, this clever feature detects when your device has been
Speaker 2: idle for a long time, like sitting on your nightstand overnight.
Speaker 2: It puts it into a much deeper sleep state. Okay,
Speaker 2: it only allows brief periodic wakeups for really essential app sinking,
Speaker 2: dramatically improving battery life during those long idle periods. M
Speaker 2: also extended full data encryption to external storage, boosting overall
Speaker 2: data security.
Speaker 1: That's a fascinating evolution. You can really see it being
Speaker 1: driven by both user demands like more storage and better battery,
Speaker 1: and also the unique constraints of mobile computing.
Speaker 2: Absolutely, it's a constant balancing act.
Speaker 1: So with all these unique components RTHL, the specialized services
Speaker 1: and the apps we install, where do they actually live
Speaker 1: on the device? Let's crack open? Metaphorically speaking, Android's internal
Speaker 1: filing system you said is far more sophisticated than a
Speaker 1: simple desktop OS.
Speaker 2: It really is. Android uses a complex moultipartition storage scheme.
Speaker 2: The specifics might vary a bit between manufacturers or even devices.
Speaker 2: But you will primarily encounter three critical partitions.
Speaker 1: Okay, what are they?
Speaker 2: First, there's system. This is the heart of Android. It's
Speaker 2: home to the core OS, all the Google supplied binaries,
Speaker 2: the core frameworks, everything that makes Android androids right. Crucially,
Speaker 2: it's designed to be mounted read only for security.
Speaker 1: So apps can't just change core OS file exactly.
Speaker 2: And as we mentioned with KitKat, dm verity, which is
Speaker 2: actually a feature of the Linux device map or subsystem,
Speaker 2: acts like that, cryptographic checks them. It ensures the system
Speaker 2: partition hasn't been tampered with. It's a significant defense and
Speaker 2: depth measure.
Speaker 1: Okay, system is the read only OS core. What else?
Speaker 2: Then? You have data. This is your space. It houses
Speaker 2: all your user data, your installed applications, their private data settings, everything.
Speaker 1: My photos, my app settings.
Speaker 2: All that stuff. And within data data, each app gets
Speaker 2: its own unique reverse DNS name subdirectory like comm dot
Speaker 2: example dot myapp. This provides script isolation between app.
Speaker 1: So one app can't easily peek into another's private files.
Speaker 2: Not easily, No, that's the point. And to protect your
Speaker 2: privacy further, this entire data partition can be encrypted. This
Speaker 2: feature was enabled by default starting with Lollipop using another
Speaker 2: device mapp or mechanism called dmcrypt. It encrypts data before
Speaker 2: it's even written to the physical.
Speaker 1: Storage, so even if someone physically gets the storage chip,
Speaker 1: the data is scrambled pretty much.
Speaker 2: Yes, without the key, it's just.
Speaker 1: Noise, okay, system data. What's through one.
Speaker 2: The third main one is cash. It's often overlooked, but
Speaker 2: it's vital for things like over the air or OTA
Speaker 2: updates and system recovery. It's where validated update packages are
Speaker 2: temporarily stored before they get installed.
Speaker 1: Ah, temporary storage for updates.
Speaker 2: Right and beyond these main partitions, we also have something
Speaker 2: called opaque binary blobs or obb's.
Speaker 1: OBB sounds mysterious, ah a little.
Speaker 2: They weren't true partitions themselves. They basically allow developers to
Speaker 2: package up large amounts of additional data up to two
Speaker 2: GB for their apps. Think big game assets, high res maps,
Speaker 2: multimedia files.
Speaker 1: Stuff that doesn't fit easily in the main app package exactly.
Speaker 2: These are typically encrypted vfat filesystem images. They get mounted
Speaker 2: on demand by a background service, a demon called vold,
Speaker 2: again leveraging the kernel's device mapper. It all happens pretty
Speaker 2: transparently to the application itself.
Speaker 1: Interesting. So we have these real storage partitions backed by
Speaker 1: physical flash memory. But you also mentioned pseudo filesystems. That
Speaker 1: sounds different. What exactly are those and what vital role
Speaker 1: do they play.
Speaker 2: Pseudo filesystems are indeed fascinating and really important for understanding
Speaker 2: how Android works under the hood. Unlike system or data,
Speaker 2: they aren't backed by physical storage at all.
Speaker 1: No files on a chip somewhere, nope.
Speaker 2: Instead, they're maintained dynamically directly by the kernel using in
Speaker 2: memory data structures and special functions called callbacks. Think of
Speaker 2: them as dynamic windows into the kernel's live operations in
Speaker 2: current state, like a live That's a great analogy. For instance,
Speaker 2: prof SIMS. The process file system is essential for tools
Speaker 2: like top or profits. It gives you a live view
Speaker 2: and all the running processes and threads, their memory usage,
Speaker 2: CPU time, et cetera. Then there's CYFTS. This allows userspace programs,
Speaker 2: even simple shell commands, to directly query and sometimes interact
Speaker 2: with hardware devices managed by the kernel like how well.
Speaker 2: For example, you could potentially control your device's vibrator by
Speaker 2: simply writing a millisecond value to a specific file within CIFTS.
Speaker 2: Maybe something like cysclass dons output vibrator or noble.
Speaker 1: Seriously, you can just write to a file to make
Speaker 1: the phone.
Speaker 2: Vibrate in many cases. Yes. Other important ones include debugs
Speaker 2: for debugging kernel features and selenics for interacting with the
Speaker 2: Selenic security subsystem. The key thing is these file systems
Speaker 2: always reflect the most up to date data from the kernel,
Speaker 2: and changes made to writeable files here often take effect immediately,
Speaker 2: though they usually don't persist across reboots.
Speaker 1: So wow, we have these distinct partitions for the OS
Speaker 1: and user data, physical storage obbs for extra app data
Speaker 1: in these dynamic pseudo filesystems, reflecting the live kernel state
Speaker 1: with all its complexity. How does an Android device even
Speaker 1: begin to start up? It sounds like an incredibly intricate
Speaker 1: dance to bring the whole system online.
Speaker 2: It truly is an intricate choreography, as Levin puts it,
Speaker 2: and it starts long before you even see the Android
Speaker 2: logo pop.
Speaker 1: Up, Before Android itself.
Speaker 2: Yeah, the process begins deep down to the device's firmware.
Speaker 2: This is somewhat like a PC's BIOS or U e
Speaker 2: fi on modern system on chip or soaky devices. This
Speaker 2: initial phase is actually quite complex. It involves various specialized
Speaker 2: subprocessors working together like Qualcom's RPM create cores, Adrino GPU,
Speaker 2: Hexagon DSP, each managing critical hardware tasks, making sure the
Speaker 2: basic system is stable and ready before the main Android
Speaker 2: bootloader even gets loaded.
Speaker 1: So the chip itself has its own little startup sequence exactly.
Speaker 2: This initial firmware then loads a secondary bootloader, which eventually
Speaker 2: control off to Android's own bootloader.
Speaker 1: Okay, now we're getting closer to Android.
Speaker 2: Right, and most Android bootloaders support the fast boot protocol.
Speaker 2: This is a simple text based mechanism that works over
Speaker 2: a USB connection.
Speaker 1: Ah, I've heard a fast boot for flashing realms and stuff.
Speaker 2: Precisely, it's how power users can flash new system images,
Speaker 2: update individual components like the radio, firmware, or even oma,
Speaker 2: unlock their device.
Speaker 1: Unlocking the bootloader.
Speaker 2: Kiss and it's important to remember while unlocking, freeze your
Speaker 2: phone to load custom firmware and allows for all sorts
Speaker 2: of modifications. It also completely wipes your data.
Speaker 1: Partition wipes everything wire.
Speaker 2: For security, it prevents an attacker from just unlocking your
Speaker 2: device to bypass your PI or password and then copying
Speaker 2: off all your personal data from data. It's a critical safeguard.
Speaker 1: Makes sense so after the bootloader does its thing.
Speaker 2: After its work, the bootloader loads the boot image. This
Speaker 2: series typically contains two key things, right, the Linux kernel
Speaker 2: itself and an initial RAM disc or any tramps.
Speaker 1: Any tramps like a temporary file.
Speaker 2: System sort of. But unlike traditional Linux, where the an
Speaker 2: TRAMS is usually discarded after the real root file system
Speaker 2: is mounted, Android keeps this inny trams resident in memory.
Speaker 2: It actually provides the initial root file system environment. Okay,
Speaker 2: And from within this inne trams environment, the kernel then
Speaker 2: launches the pivotal INNY process. This process gets process ID
Speaker 2: one or PID one.
Speaker 1: PID one the first one.
Speaker 2: The very first user space process started by the kernel.
Speaker 2: It's responsible for launching basically everything else in the user
Speaker 2: mode world, and famously in Unix like systems, PID one
Speaker 2: is special. You can't kill it. This marks that critical
Speaker 2: transition from kernel mode operation to user mode operation.
Speaker 1: Right, that transition from kernel to user mode orchestrated by
Speaker 1: in knit as PID one, that's where the Android system
Speaker 1: we actually interact with really begins to take shape. You
Speaker 1: called it the progenitor of all other processes. What are
Speaker 1: the core responsibilities of this innit process? Why is it
Speaker 1: so foundational?
Speaker 2: In it is absolutely foundational, I mean just like it's
Speaker 2: Unix namesake. Its primary job is to bring the rest
Speaker 2: of the system up in user mode.
Speaker 1: How does it know what to do?
Speaker 2: It achieves this by parsing its configuration files. These are
Speaker 2: known as dot rc files, typically found in the root
Speaker 2: directory and system mets in it. These files are essentially scripts.
Speaker 2: They contain commands and declarations that tell an in which
Speaker 2: services to start, which filesystems mounting, system read only and
Speaker 2: data read write, and what permissions and ownership to set
Speaker 2: on various files and device nodes.
Speaker 1: So it's like the master script for booting Android pretty much.
Speaker 2: Yeah. It also manages system properties. These are dynamic configuration
Speaker 2: values kind of like global variables for the system. They
Speaker 2: get read initially from files like default dot prop and
Speaker 2: system build dot prop. That build dot prop file contains
Speaker 2: tons of info about your specific device bill okay and
Speaker 2: beyond just starting things, and it takes on additional critical roles.
Speaker 2: It acts as evented listening for kernel events, signaling hardware
Speaker 2: changes like when you plug in headphones or a USB drive,
Speaker 2: and takes appropriate action. It also incorporates watchdog functionality to
Speaker 2: monitor system health and potentially reboot if things get stuck.
Speaker 1: So it starts everything, manages configuration, and keeps an eye
Speaker 1: on hardware and system health.
Speaker 2: In essence, yes, and it dictates how the entire Android
Speaker 2: system starts up and ensures that vital services are launched
Speaker 2: and maintained. It's designed to be incredibly robust, and importantly,
Speaker 2: its operation can't be easily altered from user space. Once
Speaker 2: the system is running, any significant modification usually requires flashing
Speaker 2: a new, properly signed boot image.
Speaker 1: Okay, so in it is the grand conductor for the
Speaker 1: whole startup orchestra. But beyond that initial orchestrator, Android runs
Speaker 1: countless background services. These demons that handle everything from network
Speaker 1: connections to crash reports. Let's maybe highlight a few of
Speaker 1: the most critical ones that keep your phone running seamlessly
Speaker 1: behind the scenes.
Speaker 2: Absolutely, these demons are the silent workhourses. You're right, They
Speaker 2: operate tirelessly in the background, and you often only notice
Speaker 2: them well when something goes wrong.
Speaker 1: Which ones are essential?
Speaker 2: Okay? First up service manager. Think of this as Android's
Speaker 2: central phone book or directory for almost all other operating
Speaker 2: system services. The phone book, Yeah, any application or system
Speaker 2: component that needs to interact with another core service. Say
Speaker 2: asking the location manager for GPS data, or telling the
Speaker 2: window manager to draw something, or accessing the camera service,
Speaker 2: it must first consult Service Manager. It asks service manager
Speaker 2: for a reference like a handle to that specific service,
Speaker 2: so it connects everything. It's the central hub for finding services. Yes,
Speaker 2: Without it, interprocess communication or IPC would be severely crippled.
Speaker 2: Services couldn't even register their presence within the system for
Speaker 2: others to find them. Its actual code is surprisingly small,
Speaker 2: but its importance to the entire Android framework is immense.
Speaker 1: Okay, service Manager is the connector what else next?
Speaker 2: Zygote. This is one of Android's most unique and highly
Speaker 2: optimized innovations, specifically for launching applications quickly.
Speaker 1: Zygote like the biological.
Speaker 2: Term exactly because it forks. Instead of each app starting
Speaker 2: its own full Java virtual machine from scratch, which would
Speaker 2: be slow in memory intensive, Zygote preloads the core libraries
Speaker 2: it starts up early in the boat process, initializes a
Speaker 2: Dalvic VM or now IRT, and preloads all the common
Speaker 2: Android framework classes and resources into.
Speaker 1: Memory, so it gets everything ready beforehand.
Speaker 2: Precisely, when you tap an app icon to launch it,
Speaker 2: the system doesn't start a new VM. Instead it tells
Speaker 2: Zygot to fork itself. Forking creates a near instant copy
Speaker 2: of the zydote process, inheriting all that preloaded goodness. This
Speaker 2: new process then specializes itself into the app you wanted
Speaker 2: to run.
Speaker 1: Ah, so it's like having a runner already warmed up
Speaker 1: and waiting right at the finish line.
Speaker 2: That's a perfect analogy. Camping by the finish line. It
Speaker 2: dramatically decreases application startup time by maximizing shared memory. This
Speaker 2: makes Android incredibly efficient, especially considering its application layer is
Speaker 2: largely Java based, and modern Android with sixty four bit
Speaker 2: support actually maintains both thirty two and sixty four bit
Speaker 2: Zygo instances for compatibility with all the different apps out there.
Speaker 1: Oh that's clever. Okay, service manager's zygot. What about when
Speaker 1: things go wrong?
Speaker 2: Apps crash sometimes inevitably, Yes, yeah, and that's where debugger
Speaker 2: comes in. This is androids building crash reporting mechanism. Conceptually,
Speaker 2: it's similar to crash reporter on iOS.
Speaker 1: Or macOS, so it catches crashes.
Speaker 2: Yeah. When an application receives a fatal signal like a
Speaker 2: segmentation fault where it tries to access memory it shouldn't,
Speaker 2: or an the illegal instruction. Debuggered automatically steps in. It
Speaker 2: attaches to the feeling process, inspects its memory state, gathers
Speaker 2: information about the threads, registers and the call stack leading
Speaker 2: up to the crash. Okay, and then it generates a tombstone.
Speaker 1: At tombstone morbid name a.
Speaker 2: Little yeah, but it's basically a compact crash report. It
Speaker 2: gets saved in a specific directory, usually dated tombstones. It
Speaker 2: provides essential autopsy services what went wrong, where and maybe why,
Speaker 2: without needing to generate huge, multi megabyte core dump files,
Speaker 2: which just aren't practic on mobile devices with limited storage.
Speaker 1: So a quick summary of the crash scene.
Speaker 2: Exactly, very useful for developers and sometimes for power users
Speaker 2: trying to diagnose issues.
Speaker 1: Okay, one more critical demon.
Speaker 2: Let's talk about Installed. This demon is responsible for the
Speaker 2: rather intricate process of installing and removing application packages the
Speaker 2: APK files.
Speaker 1: You mean it just copies the APK file.
Speaker 2: Oh, it's much more than that. Installed sets up and
Speaker 2: maintains the complex directory structure needed for each app. For example,
Speaker 2: it creates the apps private data directory under data data,
Speaker 2: sets the correct Linux user ID and group ID ownership,
Speaker 2: and applies the right file permissions. It also handles placing
Speaker 2: the ATK itself maybe in data app and managing private
Speaker 2: app libraries.
Speaker 1: So it sets up the apps home directory and permissions right,
Speaker 1: and it.
Speaker 2: Even handles more complex tasks like migrating directory structures when
Speaker 2: features like multi user support were introduced back in Jellybean.
Speaker 2: A key principle Intalled follows is least privilege, meaning meaning
Speaker 2: it starts with high privileges, maybe even root to do
Speaker 2: things like create directories owned by specific app UIDs, but
Speaker 2: as soon as those tasks are done, it drops those
Speaker 2: extra privileges, minimizing the potential attack surface if it were
Speaker 2: ever compromised.
Speaker 1: Smart Okay, it's clear that Android is this incredibly complex,
Speaker 1: finely tuned machine. But with so many moving parts, so
Speaker 1: many demons and apps interacting, security has to be paramount.
Speaker 1: Android has certainly faced its share of challenges over the years.
Speaker 1: So how is androids security model actually structured? Starting from
Speaker 1: those Linux foundations we talked about and building.
Speaker 2: Up That's right, security is woven in at multiple layers.
Speaker 2: Android takes the standard Linux security model user IDs, group IDs,
Speaker 2: file permissions and gives it a really novel interpretation, especially
Speaker 2: for its time. Instead of Linux users mapping directly to
Speaker 2: human users sitting at the device. Android assigns unique users,
Speaker 2: specifically application IDs aids to individual applications.
Speaker 1: So each app is its own user essentially.
Speaker 2: Yes, When an app is installed, the package manager service
Speaker 2: working with installed assigns at a unique AID, typically in
Speaker 2: arrange like ten thousand to maybe ninety thousand. This automatically
Speaker 2: isolates applications from each other at the kernel level.
Speaker 1: How does that isolate them?
Speaker 2: Because the kernel enforces standard Linux file permissions based on
Speaker 2: these aids. By default, an app running with eight one
Speaker 2: seven fifty cannot access files owned by eight one seven
Speaker 2: five to one unless permissions are explicitly granted somehow. It's
Speaker 2: the same principle that keeps different human users separated on
Speaker 2: a traditional uniax server, but applied to apps.
Speaker 1: Okay, that's the basic Linux level isolation.
Speaker 2: What else beyond the foundation? We have selinicx, the mandatory
Speaker 2: access control framework which touched on earlier, introduced properly in
Speaker 2: Jellybean and made enforcing in later versions.
Speaker 1: The strict security guard exactly.
Speaker 2: Selenicx operates alongside the traditional permissions, but adds a much
Speaker 2: stricter layer. It enforces a system wide policy that dictates
Speaker 2: exactly what operations each process or domain in SELinux terms
Speaker 2: is allowed to perform on which types of objects like files, sockets,
Speaker 2: or other processes, even if traditional permissions would allow an action.
Speaker 2: If the CYLINICX policy forbids it, it's blocked.
Speaker 1: So it prevents even privileged processes from misbehaving.
Speaker 2: Precisely, it prevents processes from operating outside their strictly defined bounds,
Speaker 2: even if they somehow get compromised. Samsung's k and Ox platform,
Speaker 2: for example, relies heavily on selnics for its enhanced security features.
Speaker 1: Okay, user IDs for apps, selnics anything.
Speaker 2: Else capabilities are also critical in the Linux kernel. These
Speaker 2: break down the traditional all powerful root user privilege into smaller,
Speaker 2: more distinct chunks.
Speaker 1: Like specific superpowers instead of one big one kind.
Speaker 2: Of yeah, so a process like installed doesn't need full
Speaker 2: root access all the time. It might only need the
Speaker 2: capability to change file ownership cap shen or bypass directory
Speaker 2: permissions captain cover ride for specific tasks. By only granting
Speaker 2: the necessary capabilities, the potential damage if that process is
Speaker 2: compromised is significantly reduced. It adheres to that principle of
Speaker 2: least privilege.
Speaker 1: Got it, minimize power where possible.
Speaker 2: And finally, for data at rest, the data sitting on
Speaker 2: your phone storage, Android offers robust encryption. We mentioned dmcrypt,
Speaker 2: using the device mapper to encrypt the entire data partition,
Speaker 2: which became default and Lollipop and dm verity insures the
Speaker 2: system partitions integrity, preventing malicious modification of the OS itself.
Speaker 2: These ensure that even if someone bypasses the lock screen
Speaker 2: or gets physical access to the storage chips, your data
Speaker 2: remains confidential and the OS integrity is maintained.
Speaker 1: That's a pretty comprehensive security stack, layers upon layers. But
Speaker 1: what about rooting. We hear about that all the time,
Speaker 1: power users, enthusiasts, motters often root their devices. How does
Speaker 1: that fit into this intricate security picture you just described.
Speaker 2: Ah, rooting, It's truly a double edged sword, no question
Speaker 2: about it. Also well for power users, for moters, for
Speaker 2: security researchers. Rooting unlocks tremendous advantages. It gives you complete
Speaker 2: unrestricted control over the entire system. You can install custom
Speaker 2: operating systems ROMs, use advanced diagnostic tools, perform specialized security
Speaker 2: audits block ads at the system level, install apps that
Speaker 2: require deep system access for things like backup or firewalling,
Speaker 2: things far beyond what stock Android permits, so.
Speaker 1: Lots of power and flexibility, immense power.
Speaker 2: However, from a security standpoint, rooting as leven states essentially
Speaker 2: entirely compromises the device's security as it was designed by
Speaker 2: Google and the manufacturers entirely compromises.
Speaker 1: That sounds bad.
Speaker 2: It means that the fundamental security model based on app
Speaker 2: isolation and restricted privileges is bypassed. If an adversary, maybe
Speaker 2: through a malicious app you install after routing, gains root access,
Speaker 2: they can do anything. They can bypass PNS. They can
Speaker 2: read data from any app, they can copy the entire
Speaker 2: data partition, install keyloggers, spyware, you name it, so.
Speaker 1: The walls between apps crumble completely.
Speaker 2: We've seen real world exploits over the years, like Geohat's
Speaker 2: famous tow root exploit, which cleverly used a bug in
Speaker 2: the Linux kernel specifically CVE twenty fourteen three one five
Speaker 2: three to gain root access on many devices with just
Speaker 2: a tab, or the fake ID vulnerability, which wasn't about
Speaker 2: getting root, but allowed malicious apps to essentially forge credentials
Speaker 2: and impersonate trusted applications, so these vulnerabilities pop up, they do,
Speaker 2: and while Google works tirelessly to patch these vulnerabilities through
Speaker 2: security updates, the act of choosing to root fundamentally changes
Speaker 2: the device's security posture. It makes it inherently more vulnerable,
Speaker 2: especially if the root access method itself isn't from an
Speaker 2: absolutely trusted source, or if the user isn't careful about
Speaker 2: what they grant root privileges too. Afterwards. It really highlights
Speaker 2: that constant tension and Android between its open, flexible, customizable
Speaker 2: nature and the need for robust, reliable security for everyone.
Speaker 1: It's a very delicate balance indeed. And you know, if
Speaker 1: we connect this back to the broader picture of Android's
Speaker 1: internal workings, thinking about Zygo, sharing memory or optimizing code,
Speaker 1: it sounds like the system is in this constant battle
Speaker 1: for efficiency, especially when it comes to memory, particularly given
Speaker 1: its general lack of traditional swap space like a desktop
Speaker 1: OS might have.
Speaker 2: You've hit on a really crucial point there. Android's design,
Speaker 2: especially with Delvic and later art, places a huge emphasis
Speaker 2: on maximizing shared memory. This is absolutely vital on devices
Speaker 2: with constrained rams.
Speaker 1: Zigo is key there.
Speaker 2: So I go to central yes by pre loading all
Speaker 2: those common framework classes and resources. It ensures that the
Speaker 2: vast majority of the memory used by the core Android
Speaker 2: system is shared across all running apps. Tools leven mentions
Speaker 2: like pro crank or a librank can actually show you this.
Speaker 2: They distinguish between an app's total memory usage RSS residence
Speaker 2: set size and its unique usage USS unique set side, and.
Speaker 1: The unique part is small.
Speaker 2: Often yes, you might see that the unique footprint the
Speaker 2: USS of many apps is just a few megabytes, maybe
Speaker 2: eighty five percent, ninety percent or even more of their
Speaker 2: total RSS is actually shared memory pages shared thanks to Zygote,
Speaker 2: shared thanks to precompiled art files like boot dot oat
Speaker 2: that contained framework code, and even shared things to a
Speaker 2: Linux kernel feature called Kernel sain Page Merging or KSM KSM.
Speaker 1: What does that do?
Speaker 2: KSM is a kernel demon that periodically scans physical memory
Speaker 2: looking for identical pages. If it finds two or more
Speaker 2: identical pages, it merges them into a single physical page,
Speaker 2: marks it as copy on right, and frees up the duplicates.
Speaker 2: It happens transparently to the.
Speaker 1: Applications, so more automatic memory saving.
Speaker 2: Exactly all these mechanisms work together to make Android remarkably
Speaker 2: memory efficient. However, you're right about the swap space.
Speaker 1: Most Android devices don't use it.
Speaker 2: Traditionally no using flash memory the type of storage and
Speaker 2: phones for frequent swap operations. Writing memory pages out to
Speaker 2: DISC when RAM gets full would drastically reduce this lifespan.
Speaker 2: Flash memory has a limited number of right cycles.
Speaker 1: Okay, so no swap cushion. What happens when memory runs
Speaker 1: out right without swap?
Speaker 2: Out of memory or OHAM conditions become a much more
Speaker 2: immediate threat. If the system truly runs out of available RAM,
Speaker 2: the pernel might start randomly killing processes, or the whole
Speaker 2: system could become unstable and crash or reboot. Not good,
Speaker 2: definitely not good for user experience. To prevent this worst
Speaker 2: case scenario, Android emplays another one of those specific androidisms,
Speaker 2: the LMANKD or low memory killer demon.
Speaker 1: Low memory killer sounds ominous.
Speaker 2: It does. The ALMINKD runs as a kernel module or
Speaker 2: demon and continuously monitors the system's memory pressure based on
Speaker 2: predefined thresholds and the omscore edge value assigned to each
Speaker 2: running process, which indicates its importance. The elman kady preemptively
Speaker 2: kills less important background processes before the system hits a
Speaker 2: critical om state.
Speaker 1: So it sacrifices background apps to save the foreground app
Speaker 1: and the system.
Speaker 2: That's the idea. It's a pragmatic, sometimes aggressive approach. Users
Speaker 2: might notice apps they haven't used recently need to reload
Speaker 2: fully when they switch back, but it's deemed necessary to
Speaker 2: keep the currently active app responsive and prevent the entire
Speaker 2: system from grinding to a halt or crashing due to
Speaker 2: memory starvation. It really reflects the practical rea of managing
Speaker 2: limited resources on mobile devices.
Speaker 1: Wow, what an incredible journey we've taken. Guided by Jonathan
Speaker 1: Levin's unique perspective and Android internals, We've really taken a
Speaker 1: deep dive, haven't we?
Speaker 2: We really have.
Speaker 1: We went from Android's Linux foundations, traced its rapid evolution
Speaker 1: through pivotal versions like Lollipop and kit Kat with all
Speaker 1: those neat features like artt and Doze.
Speaker 2: The filesys details.
Speaker 1: Yeah, explored the intricate dance of its filesys system data,
Speaker 1: those pseudo filesystems, and that complex boot process starting way
Speaker 1: down in the firmware, and.
Speaker 2: The demons in its Zygote service manager installed the unsung.
Speaker 1: Heroes exactly unveiled the critical roles of Inausley and those
Speaker 1: essential demons and navigated the complex layers of security UIDs
Speaker 1: so Linux capabilities, encryption, and finally the constant battle for
Speaker 1: memory management that orchestrates it all.
Speaker 2: And if we connect all that back to the bigger picture,
Speaker 2: hopefully you now possess a far richer understanding of of
Speaker 2: the frankly ingenious engineering that's humming away inside the device,
Speaker 2: likely in your hand or pocket right now. Yeah, this
Speaker 2: deep dive, I hope, has illuminated how Android meticulously balances
Speaker 2: its open source nature, that flexibility with an unyielding need
Speaker 2: for robust security, and how it constantly optimizes resources to
Speaker 2: deliver the seamless powerful experience you've come to expect, all
Speaker 2: without needing to weidhe through millions of lines of course
Speaker 2: code yourself.
Speaker 1: So what does this all mean for you listening right now? Android? Yeah,
Speaker 1: it's an open source system, But how many people can
Speaker 1: really sit down and sift through those millions of lines
Speaker 1: of Java, c C plus plus XML all the rest
Speaker 1: to figure out how it actually works, let alone connect
Speaker 1: those intricate details back to their daily experience with their phone.
Speaker 2: It's a huge undertaking, it is.
Speaker 1: We hope this deep dive has revealed some of that
Speaker 1: hitting complexity, maybe some surprising facts that make Android so powerful,
Speaker 1: so adaptable, and also so resilient despite the challenges. The
Speaker 1: real question is armed with this new found understanding of
Speaker 1: its depths, what aspect of androids hidden world will you
Speaker 1: explore next