The 4.8 kernel was released on October 2nd. This also marked the start of the merge window for the 4.9 kernel. The merge window is the time period when kernel subsystem maintainers send their pull requests for new features to be included in the 4.9 kernel. Here are a few features pulled into the 4.9 kernel that might be of interest for Fedora users.

Integrated Sensor Hub

Intel merged support for the Intel Integrated Sensor Hub (ISH). This enables use of sensor coprocessors on newer Intel chips. The description of the feature claims this should help with CPU power usage, since sensor processing can be offloaded to the sensor coprocessor. It remains to be seen what impact this will actually have on end users, since CPU low power modes can be affected by many parts of the system. Having this driver is an important part of getting the best possible power management on Linux.

SELinux support for overlayfs

Container technology is a hot topic everywhere. overlayfs is a union file system used to implement core parts of container technologies. Filesystems need additional hooks to work properly with SELinux, and this merge window brought in changes to add SELinux support for overlayfs. This is important to give containers additional security.

Virtually mapped stacks

As part of other ongoing security work, x86 now has an option to have virtually mapped stacks. This makes it much easier to detect stack overflows and other stack errors. With virtually mapped stacks, errors are more likely to cause faults instead of corrupting other structures. This feature also has the advantage of helping to find drivers that incorrectly using stack addresses for DMA. Several problems have been found and corrected using this patch set already, which is a positive indication that it will be useful in the future.


The arm64 architecture enabled CONFIG_DEBUG_RODATA by default. Despite the word debug in the name, this option provides important security features by marking appropriate areas of the kernel as read only and/or no execute. x86 made a similar change earlier this year. With the move to make arm64 a primary architecture in Fedora, it’s important to see arm64 continue to gain feature parity with x86.

These are just a few of the many kernel features in this merge window. LWN always provides excellent coverage of each kernel merge window in depth. These kernel features are available in Fedora Rawhide right now and will be available in Fedora stable releases in a few months when 4.9 is officially released.

Image courtesy Darrin Henein – originally posted to Unsplash here.