The mysterious microcode: Intel is issuing updates for all its CPUs from the last five years but you might not benefit

The Spectre and Meltdown security holes found in Intel and to a lesser extend AMD CPUs is not only one of the most serious, but also one of the most confusing tech issues that I can recall.

We are all used to the idea of patching to fix security holes, but normally that is all you need to do. Run Windows Update, or on Linux apt-get update, apt-get upgrade, and you are done.

This one is not like that. The reason is that you need to update the firmware; that is, the low-level software that drives the CPU. Intel calls this microcode.

So when Intel CEO Brian Krzanich says:

By Jan. 15, we will have issued updates for at least 90 percent of Intel CPUs introduced in the past five years, with updates for the remainder of these CPUs available by the end of January. We will then focus on issuing updates for older products as prioritized by our customers.

what he means is that Intel has issued new microcode for those CPUs, to mitigate against the newly discovered security holes, related to speculative execution (CPUs getting a performance gain by making calculations ahead of time and throwing them away if you don’t use them).

Intel’s customer are not you and I, the users, but rather the companies who purchase CPUs, which in most cases are the big PC manufacturers together with numerous device manufacturers. My Synology NAS has an Intel CPU, for example.

So if you have a PC or server from Vendor A, then when Intel has new microcode it is available to Vendor A. How it gets to your PC or server which you bought from Vendor A is another matter.

There are several ways this can happen. One is that the manufacturer can issue a BIOS update. This is the normal approach, but it does mean that you have to wait for that update, find it and apply it. Unlike Windows patches, BIOS updates do not come down via Windows update, but have to be applied via another route, normally a utility supplied by the manufacturer. There are thousands of different PC models and there is no guarantee that any specific model will receive an updated BIOS and no guarantee that all users will find and apply it even if they do. You have better chances if your PC is from a big name rather than one with a brand nobody has heard of, that you bought from a supermarket or on eBay.

Are there other ways to apply the microcode? Yes. If you are technical you might be able to hack the BIOS, but leaving that aside, some operating systems can apply new microcode on boot. Therefore VMWare was able to state:

The ESXi patches for this mitigation will include all available microcode patches at the time of release and the appropriate one will be applied automatically if the system firmware has not already done so.

Linux can do this as well. Such updates are volatile; they have to be re-applied on every boot. But there is little harm in that.

What about Windows? Unfortunately there is no supported way to do this. However there is a VMWare experimental utility that will do it:

This Fling is a Windows driver that can be used to update the microcode on a computer system’s central processor(s) (“CPU”). This type of update is most commonly performed by a system’s firmware (“BIOS”). However, if a newer BIOS cannot be obtained from a system vendor then this driver can be a potential substitute.

Check the comments – interest in this utility has jumped following the publicity around spectre/meltdown. If working exploits start circulating you can expect that interest to spike further.

This is a techie and unsupported solution though and comes with a health warning. Most users will never find it or use it.

That said, there is no inherent reason why Microsoft could not come up with a similar solution for PCs and servers for which no BIOS update is available, and even deliver it through Windows Update. If users do start to suffer widespread security problems which require Intel’s new microcode, it would not surprise me if something appears. If it does not, large numbers of PCs will remain unprotected.

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