Sam

Hellaphone: Replacing the Java in Android

John Floren

Sandia National Labs

July 2012

Collaborators: Joshua Landgraf, Joel Armstrong

Biography

Computer engineer by training (RIT)

Been interested in operating systems since high school

Work for Sandia National Labs, California

• High performance computing

• Mobile

• Security

I like open source and Sandia is down with that
Goal: open up as much of my work as possible

Smartphones

• Totally ruling the world

• A computer in my pocket? Awesome!

• It can make phone calls too?

• Nifty sensors: camera, GPS, accelerometer

• Read email, browse the web, take pictures, get driving
directions, play games

• Manage your passwords, 2 factor auth, Google Wallet

Why smartphones kinda suck

Blackberry, iPhone, Windows: all closed-source

RIM will decrypt your messages for the government [6][5]

iPhone

• Tracks your movements [1]

• DoS attack via SMS [2]
Windows

• Nobody has one!

• DoS'd via SMS [7]
CarrierlQ [3]

But Android is still cool, right?

Linux-based
Open-source

Tons of devices (phones, tablets, laptops)

Write your own applications-no developer fees, no market

fees!

You can hack the OS if you want

Big community of developers and OS hackers

Android kinda sucks too

I have to program in WHAT?

Vendors have no incentive to update the OS

• How much do you trust Joe Random's ICS Rom?
Security ain't so hot

• DEF CON 19: fake OTA updates

• CarrierlQ

• Malicious apps [4]

About 15 million lines of code, not including Linux.

• Not very documented-hope you like digging!

1 .2 GHz processor, 512 MB of RAM, runs like a dog

Android as a Linux platform

• Android is unattractive for hacking, sure

• Really just a thick layer of Java spread on top of a thin Linux
cracker

• Mostly standard Linux underneath

• Comes with a little busybox environment

• Cyanogenmod ships a rather nice environment with bash etc.

• Let's scrape away the Java and build on Linux

• Bonus: we'll get tons of compatible hardware with all the
drivers already written

Inferno

Open-source operating system from Bell Labs, now owned by
Vita Nuova

Implements the Dis virtual machine

Runs natively or hosted on Linux/Windows/OS X/Plan 9

Inspired by Plan 9

Compiles fast, launches fast

• Runs in a few megabytes

• About 1 million LOC total

• This includes the applications and code for native booting
(which we don't use)

Why not run it on top of Android's Linux?

• We get all the hardware drivers (binary blobs, yay!)

• Makes updating Inferno easy-no flashing ROMs

vita nuova

Android - Java = Linux

The first thing we do, let's kill all the Java

Every Java process spawns from "zygote"

Eliminate it from /init.rc

But / is reset every boot!

You can build your own custom ROM

Or use our script to grab the running boot image, modify it,

and reflash

Android + Inferno = Hellaphone

Adapt Inferno to build for Android

Use AGCC script to build Inferno with Android compilers and
libs

Most of the Linux code is suitable

Some tweaks were needed in bits of assembly or C

Had to create support for various bits of hardware

• Framebuffer adapted from OLPC code

• Mouse code to parse touchscreen inputs

• Convert /dev/input events to text and make it available
Hack the window manager to make it suitable for a phone.

The old Inferno window manager

It has a browser too

Phone-specific stuff

devphone talks to the radio

• Presents a file system interface

• To make a phone call: echo 'dial 15551234567' >
/phone/phone

• To receive incoming calls, read from /phone/phone

• Read will block until a call is incoming

• Similar interface for SMS

Nobody wants to make phone calls like that

So we wrote a dialer app and an SMS app

Also made early drafts at WiFi and audio drivers (both

semi-functional)

Dialing application

SMS application

17405^^H

5554443322
5551234567

Them: The client used to send
messages should prepend "Me: "
messages it sends, then add

7_

Neat things to try

Inferno sandboxing - one instance of OS per app
Security hacks

• If accelerometer reads > 10G, wipe the SD card
Fun with 9P

• Easy to access your files at home

• Easy to share files with nearby phones

• Use 9P to export your phone's devices and control them from
your PC

• Anti-theft programs are now easy

• Just import your phone's GPS device and camera

• (Thief is probably pretty perplexed anyway)

Conclusion

It's not that hard to strip down Android for your own purposes
With a bit more work, Inferno could be a viable smartphone
OS

• It's fast

• It's light

• It's easy to work on

• It already comes with a bunch of software and infrastructure,
you're not going from scratch

• No app store, but if you didn't write it yourself, you can't trust it
anyway, right?

Get in!

Code at http : / /bitbucket . org/ f loren/ inferno

Bibliography I