05.03.2021

Friday in the Void: OpenSSL and Kernel Hardening

The previously announced OpenSSL switch is now underway. Because OpenSSL is a dependency of a large number of packages, the full rebuild process is expected to take several days. Syncing between the builders and public repositories has been suspended to ensure that the package tree remains consistent. Consequently, no new package updates will appear until the switch is complete.

Once updates appear, we recommend that you perform a complete system update to simplify the transition. Partial updates are possible, but you will need to manually trace all OpenSSL dependants installed on your system and update them atomically.


Since 2016, the default bootloader configuration in Void Linux has set the Linux kernel command-line options slub_debug=P and page_poison=1 to provide some level of kernel hardening. Kernel series 5.3 and later offer alternative measures init_on_alloc and init_on_free (see this kernel commit).

Void’s kernels come with the init_on_alloc option enabled by default where available (i.e., linux5.4>=5.4.102, linux5.10>=5.10.20 and linux5.11>=5.11.3). In most cases, you should not disable this option, as it has a fairly minimal impact on performance (within 1%). The init_on_free option is more expensive (around 5% on average) and needs to be enabled by hand by passing init_on_free=1 on the kernel command line. Similarly, init_on_alloc can be disabled if needed by passing init_on_alloc=0.

As a consequence of these changes, Void’s default kernel command-line now omits the slub_debug and page_poison options. There is a chance that your existing system still has the old options enabled. They still work in newer kernels, but have a performance impact more in line with init_on_free=1. On older hardware this can be quite noticeable. If you are running a kernel series older than 5.4, you can keep them (or add them) for extra security at the cost of performance; otherwise, you should remove them.


As always, if you experience any issues, feel free to reach out to us! You can open an issue on GitHub or seek help in the #voidlinux channel on https://freenode.net.