© 2010 VMware Inc. All rights reserved Application-level mobile virtualization Harvey Tuch, Staff Engineer, Mobile Virtualization Platform January 25 th 2012 Sponsored by MIT and VMware Academic Programs VMware: VMware Labs: labs.vmware.com

2 Agenda Mobile hypervisor distribution Virtualization at user-level on Linux Putting it together: Android VMM app Programming exercise

3 Mobile hypervisor distribution

4 Not all mobile hypervisor components can be typically provisioned by app store System software provisioned by OEM and/or carrier Maintenance of baked on bits Time to market (TTM) Market coverage What if we move system (privileged) components to application (user) level? Distribute entire hypervisor like a regular app, via app store Relax distribution constraints Performance, fidelity tradeoffs

5 Mobile hosted architecture Privileged User Host world Guest/monitor world Monitor Guest Kernel modules Host kernel VM control, device backends

6 Deprivileged hosted architecture Privileged User Host world Guest + monitor Host kernel

7 App store distribution constraints Mobile app security models, e.g. Android User-level, deprivileged execution Kernel sandboxing, restricted access to: File system Other applications Services (e.g. SMS, GPS, network) Native components via JNI Unique UID + data directory for each application

8 Agenda Mobile hypervisor distribution Virtualization at user-level on Linux Putting it together: Android VMM app Programming exercise

9 Virtualization at user-level on Linux

10 User-level virtualization Run guest as an application on host OS Guest user ISA runs 1:1 How to handle guest user exceptions? (syscall traps, page faults, etc.) How to execute guest privileged ISA? (e.g. on ARM MSR/MRS/MCR/MRC..) How to map guest adddress space to application address space on host?

11 User-level virtualization Run guest as an application on host OS Guest user ISA runs 1:1 How to handle guest user exceptions? (syscall traps, page faults, etc.) How to execute guest privileged ISA? (e.g. on ARM MSR/MRS/MCR/MRC..) How to map guest adddress space to application address space on host?

12 Guest user ISA runs 1:1

13 Guest user ISA runs 1:1

14 User-level virtualization Run guest as an application on host OS Guest user ISA runs 1:1 How to handle guest user exceptions? (syscall traps, page faults, etc.) How to execute guest privileged ISA? (e.g. on ARM MSR/MRS/MCR/MRC..) How to map guest adddress space to application address space on host?

15 Guest user syscall exception

16 Guest user syscall exception

17 Guest user syscall exception

18 Guest user syscall exception

19 ptrace system call Linux system call allowing one process to control/monitor another Used by gdb, strace Parent can inspect/modify childs: Register file Memory Parent can intercept child signals Exceptions (including syscall traps) reflected in Unix at user-level as signals Parent can single step and inject signals into child

20 ptrace based virtualization Hypervisor thread parent ptrace child thread representing guest Use ptrace : Intercept all signals (exceptions) Intercept system calls Context switch child thread between guest kernel/user Performance penalties Each exception requires switching between guest thread, host kernel, hypervisor thread, host kernel and guest thread ptrace originally only intended for debug, but now optimized to support User- mode Linux (see also Fiasco-UX)

21 ptrace exception handling while (1) { waitpid(guestPID, &status, __WCLONE | WUNTRACED);... struct user_regs regs; ptrace(PTRACE_GETREGS, vmm->currentGuestPID, NULL, &regs); int sig = WSTOPSIG(status); switch (sig) { case SIGTRAP: {... }

22 Guest user syscall exception

23 User-level virtualization Run guest as an application on host OS Guest user ISA runs 1:1 How to handle guest user exceptions? (syscall traps, page faults, etc.) How to execute guest privileged ISA? (e.g. on ARM MSR/MRS/MCR/MRC..) How to map guest adddress space to application address space on host?

24 Guest privileged ISA

25 Guest privileged ISA Sensitive + privileged instructions E.g. MCR/MRC on ARM Trap+emulate with ptrace Sensitive + non-privileged instructions E.g. MSR/MRS on ARM Paravirtualization Hypercall traps to hypervisor parent process via ptrace

26 User-level virtualization Run guest as an application on host OS Guest user ISA runs 1:1 How to handle guest user exceptions? (syscall traps, page faults, etc.) How to execute guest privileged ISA? (e.g. on ARM MSR/MRS/MCR/MRC..) How to map guest adddress space to application address space on host?

27 Guest address space mapping

28 Guest address space mapping

29 Guest address space mapping Reduced guest address space Guest kernel modifications required Guest application visible

30 Agenda Mobile hypervisor distribution Virtualization at user-level on Linux Putting it together: Android VMM app Programming exercise

31 Putting it together: Android VMM app

32 Android.apk anatomy.apk Resources Meta-data CertificatesDEX (Java) Native code (JNI)

33 Android VMM application Java frontend VM lifecycle management Display VM framebuffer contents Touchscreen input Invoke native code via JNI Native code (JNI) ptrace -based VMM Resources Guest kernel + applications (LBS VM image)

34 Agenda Mobile hypervisor distribution Virtualization at user-level on Linux Putting it together: Android VMM app Programming exercise

35 Programming exercise Implement parts of deprivileged mobile hypervisor Context switching Paravirtualized hypercall handling Run on your Android smartphone (or SDK emulator) Complete by 5 th February 2012 to enter draw to win iPad Questions and clarification to: