Dr. Dobb's | Microkernels and Virtualization: Inside a Mobile Phone

Microkernels and Virtualization: Inside a Mobile Phone

Small devices and minimal operating systems

July 10, 2007
URL:http://www.drdobbs.com/open-source/microkernels-and-virtualization-inside-a/201000360

Today we're talking with Dr. Gernot Heiser, founder and CTO of Open Kernel Labs, a company that specializes in operating systems and virtualization technology. The company's OKL4 microkernel, for instance, is used in Toshiba's W47T mobile phone.

DDJ: Gernot, from what I hear, Microsoft Vista weighs in about 600 MB. How does OKL4 measure up, in size and function?

GH: The comparison isn't quite fair. Vista is a complete operating system aimed as desktops and servers, where much functionality is needed, and memory is much less of an issue. OKL4 is a minimal OS environment aimed at a wide range of embedded systems, from smartcards via cell phones to network routers.

As such, OKL4 is designed to provide minimal functionality in order to run on very small systems, in as little as 100 KB. On the other hand it allows to run more fully-featured operating systems, such as Linux or Windows embedded, in a virtual machine.

DDJ: You say that the licensing of OKL4 by Toshiba for its W47T mobile phones is "the first end-user deployment of modern virtualization technology on mobile-phone handsets." What does virtualization have to do with mobile phones?

GH: High-end mobile phones these days are pretty powerful computers in their own right, running a wealth of media applications, productivity tools, games, and the like. Programmers writing such applications are typically not embedded-systems experts, and need a familiar, high-level OS API to work with. Furthermore, you want to run a lot of the same applications on the phone than on a laptop, such as e-mail, word processors, and so on. This need is served by operating systems such as Linux and Windows, but they are not suitable for supporting the low-level communication functionality, which needs a real-time OS. Virtualization allows running different operating systems concurrently on the same device processor.

DDJ: You also say that "OKL4's open platform protects communications firmware from interference through fault containment." Can you elaborate on this?

GH: The application stack of a high-end phone is huge, maybe 4-5 MLOC, and inherently buggy. Even the OS that supports it has bugs that can be exploited. In the past, exploits have used carefully-crafted multimedia messages to leverage a buffer overflow in the OS. With phones becoming more open, allowing users to download programs and run them on the phone, the probability of such exploits is increasing. But you don't want the cracker to subvert the communications stack and turn the handset into a jammer, that disables a complete cell for all users. By running the application stack in a virtual machine, the rest of the system can be protected against it misbehaving.

DDJ: Is there a web site that readers can go to for more information?

GH: Yes they can go to the Open Kernel Labs web site which provides more information about microkernels.