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Kindlet-Loader

KL allows selectively loading Kindlets outside of the normal sandbox. With it you can launch unsigned kindlets, and permit them full access to the filesystem and Java framework.

Supported devices

Right now KL only works on the Kindle 4, software version 4.1.0. It was compiled against the Kindlet API version 1.3.

It can most likely be ported to the Kindle 3 and Kindle Touch, but at the moment I don't have access to their Java libraries to do the porting.

Do not try to install this KL version to an unsupported software version. At best, it will not work. At worst, you may have to unbrick your Kindle afterwards.

Requirements

You need to have SSH access into your Kindle.

How it works

KL implements a custom classloader for the kindlets, skipping all the sandboxing checks: certificates, java permissions and class whitelisting.

After you've installed the KL, when launching a Kindlet for the first time, you will get a dialog asking if you want to allow it full permissions (using the custom classloader) or load it normally (inside the regular Kindlet API sandbox).

If you load it with full permissions:

  • the certificate checks will not be performed; so the kindlet can be signed with a developer key, or not signed at all, it does not matter; you will not need to install any developer certificates.

  • the kindlet will have full access to the device's filesystem, not just inside the regular sandbox -- it will be able to read and write any file.

  • the kindlet will have full access to the Java framework's classes, not just to the Kindlet API. This is not as useful as it may sound, as the Kindle Java framework is heavily obfuscated, in a manner that makes some parts of the API unaccessible for development (but still fully functional). The parts that are accessible are very hard to read and comprehend.

If you do allow full permissions to a kindlet, it will most likely fail to load the first time. Just start it again and it will be running with full permissions.

KL keeps a database in /mnt/us/system/kindlets-whitelist.txt with kindlets that are allowed full permissions, so you will only be asked once for each kindlet you launch. You can change the file at any time, or delete it altogether.

Installing

SSH into your device. Mount the root partition read-write (mntroot rw).

Copy out/@unsigned-kindlets-loader-410.jar to the device, in the folder /opt/amazon/ebook/lib. Make sure to keep the file name as-is; the @ at the beginning of the name ensures the custom classloader is seen first by the Java framework.

Re-mount the root partition read-only (mntroot ro). Restart the Java framework:

/etc/init.d/framework restart

Enjoy! :)

Un-installing

SSH into your device. Mount the root partition read-write (mntroot rw).

Remove the file @unsigned-kindlets-loader-410.jar from /opt/amazon/ebook/lib.

Re-mount the root partition read-only (mntroot ro), and restart the Java framwork.