32-bit guest additions incompatible with 64-bit kernel

[Tails developers]

Most Linux distributions support running a 32-bit userland with an amd64 kernel. Unfortunately, VirtualBox Guest Additions choke on such environment.

The kernel output messages like the following:

[   24.433817] ioctl32(VBoxService:1934): Unknown cmd fd(3) cmd(c08c5610){t:'V';sz:140} arg(ffd3e804) on /dev/vboxguest

And a bunch of others from Xorg.

This could look like a niche problem, but Tails is a live system and for maximum compatibility we ship a 32-bit userland. Shipping a 32-bit kernel (for older computers) and a 64-bit kernel for newer systems is a good compatibility/memory access compromise. Unfortunately, we also advertise VirtualBox support and thus this bug currently prevents us from shipping a 64-bit kernel.

[Tails developers]

Actually this looks like a duplicate of #8336. The later is unfortunately not assigned to guest additions as its component which is why we had not found it in the first place.