[coreboot] Removing microcode updates from blobs

ron minnich rminnich at gmail.com
Sat Dec 14 07:36:49 CET 2013

There's a knob. It's called 'microcode updates'. If you set the knob
to 'offf' the firmware image you build, and boot, may let the CPU do
very bad things to you, in unpredictable ways, at unpredictable times,
including (on some CPUs) cause very difficult to detect data
corruption because (on some CPUs) there are issues with behavior of
shared cache lines or the data path to memory.

The best part? The CPU may behave very well, 999,999,999 times out of
1000000000. It's that last misbehaving time that's going to bite you.

Don't believe me? How about this. I just typed
microcode update xeon errata
for the heck of it and:
"Intel has discovered an erratum with Dual-Core Intel Xeon 5200-series
and Quad-Core Intel Xeon 5400-series processors. The potential for
this issue to occur does not apply when using Dual-Core Intel Xeon
5000-series, Dual-Core Intel Xeon 5100-series, or Quad-Core Intel Xeon
5300-series processors.

The issue is documented in an updated version of the Intel Processor
Specification Update for all affected processors. For additional
details regarding the Intel microcode update, reference Errata AX52
(5400-series processors) or Errata AY52 (5200-series processors) in
the appropriate Intel Processor Specification Update on the Intel
website at the following

The issue can lead to server hang/reboot and it has been observed to
have this effect in recent AppLogic releases. The fix is to have the
BIOS of servers using these processors upgraded to a version that
resolves these errata."

See those three litle words: "intel microcode update". Oh, and how
about "server hang/reboot".
Gee, I can build in a 'more free' way if I'm willing to have the
occasional hang or reboot. Terrific.

People have ideas about 'free is good, so turning off microcode
updates, since it makes the code more free, must be good too'. And
that's just plain wrong.

I can't see any redeeming value to the idea of moving the microcode
updates into blobs. The point of blobs, when we created it, was to
have a place to put things we can't put directly in the coreboot repo.
It was never intended to be a destination for things already in the
repo. You're misreading the intent of that directory.

And I think it even worse to put the microcode blobs in a location in
the tree that implies, by its existence, that you can build without
them and get a more free, working firmware image.

That's why I'm so unhappy with this change. I think it's a mistake.


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