intel has released a microcode update for the spectre vunerability dated 2018/01/10 - this should eventually find its way into a bios update for reasonably current hardware.
In the meantime, after downloading from, for example, arch linux, the microcode update can be loaded like this: $ cat grub.cfg
...
initrd /boot/intel-ucode.img /boot/rootfs64.gz /boot/modules64.gz
...
note that intel-ucode.img must be the first in the list.
If successful, you should see something like this: $ dmesg | grep -i micro
microcode: microcode updated early to revision 0x21, date = 2017-11-20
microcode: sig=0x40651, pf=0x40, revision=0x21
microcode: Microcode Update Driver: v2.2.