Signed Kernel Modules

Now you can make the kernel check modules for a cryptographic signature before inserting them. Here's the detail of how it's done.
What Is Left to Do?

As shown in this article, a number of different steps are required to generate a key, sign a kernel module and place the public key into the kernel image. This still is a rough development project. In order to make it more acceptable to the kernel developers and to the Linux community in general, these steps need to be automated, making it easier to sign all kernel modules and handle the public key.

Besides the obvious need to simplify the use of this feature, some other future goals of this project include:

  • Move the RSA code into the generic crypto framework, allowing other kernel features to use it.

  • Allow more than one public key to be present in the kernel, letting multiple sources of signed kernel modules run in a single machine.

  • Simplify the signing logic to allow GPG's native signing functionality or possibly the functionality provided in the bsign program to be used, instead of the custom mod program.

Acknowledgements

I would like to thank the developers at Ericsson, who have created a kernel patch and program called digsig, for allowing me to use their port of GPG to the kernel. I previously had done this, but the implementation was horrible; thankfully, they released their port and were very helpful. The digsig kernel patch allows users to sign programs and prevents the kernel from running any program not signed. More information about this project can be found at sourceforge.net/projects/disec.

I also would like to thank my employer, IBM, for allowing me to work on this project, and Don Marti, for prodding me to finish it and write this article.

Greg Kroah-Hartman currently is the Linux kernel maintainer for a variety of different driver subsystems. He works for IBM, doing Linux kernel-related things, and can be reached at greg@kroah.com.

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