[personal profile] mjg59
A (well, now former) coworker let me know about a problem he was having with a Lenovo Thinkcentre M92p. It booted Fedora UEFI install media fine, but after an apparently successful installation refused to boot. UEFI installs on Windows worked perfectly. Secure Boot was quickly ruled out, but this could still have been a number of things. The most interesting observation was that the Fedora boot option didn't appear in the firmware boot menu at all, but Windows did. We spent a little while comparing the variable contents, gradually ruling out potential issues - Linux was writing an entry that had an extra 6 bytes in a structure, for instance[1], and a sufficiently paranoid firmware implementation may have been tripping up on that. Fixing that didn't help, though. Finally we tried just taking the Windows entry and changing the descriptive string. And it broke.

Every UEFI boot entry has a descriptive string. This is used by the firmware when it's presenting a menu to users - instead of "Hard drive 0" and "USB drive 3", the firmware can list "Windows Boot Manager" and "Fedora Linux". There's no reason at all for the firmware to be parsing these strings. But the evidence seemed pretty strong - given two identical boot entries, one saying "Windows Boot Manager" and one not, only the first would work. At this point I downloaded a copy of the firmware and started poking at it. Turns out that yes, actually, there is a function that compares the descriptive string against "Windows Boot Manager" and appears to return an error if it doesn't match. What's stranger is that it also checks for "Red Hat Enterprise Linux" and lets that one work as well.

This is, obviously, bizarre. A vendor appears to have actually written additional code to check whether an OS claims to be Windows before it'll let it boot. Someone then presumably tested booting RHEL on it and discovered that it didn't work. Rather than take out that check, they then addded another check to let RHEL boot as well. We haven't yet verified whether this is an absolute string match or whether a prefix of "Red Hat Enterprise Linux" is sufficient, and further examination of the code may reveal further workarounds. For now, if you want to run Fedora[2] on these systems you're probably best off changing the firmware to perform a legacy boot.

[1] src/include/efi.h: uint8_t padding[6]; /* Emperically needed */, says the efibootmgr source code. Unhelpful.
[2] Or Ubuntu, or Suse, or…

Bullying h/w vendors

Date: 2012-11-16 02:11 pm (UTC)
From: (Anonymous)
There was a similar, but slightly different, diamond graphics card issue in the past. In short diamond thought that releasing programming information would lead to the loss of their uboat fleet in the north atlantic.

This resulted in a campaign of people buying new graphics card contacting their marketing people once and telling them that they were buying competing hardware due to diamond's refusal to support linux. Eventually this got the desired result and, if I remember correctly, diamond paid good money for their hardware to be well supported.

Maybe the same technique would work for Lenovo and others. I will either buy hardware which explicitly supports linux or build a box out of linux compatible bits. If I never buy a windows licence then it should be easy to avoid hardware which requires it :-)

Re: Bullying h/w vendors and/or the opposite

Date: 2012-11-16 09:15 pm (UTC)
From: (Anonymous)
I bought a HP printer because it did support Linux, and I wrote HP to tell them that that was one of the main reasons that I had bought their product. Let's hope that positive reinforcement works too! :-)

Best,
Pierre.

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Matthew Garrett

About Matthew

Power management, mobile and firmware developer on Linux. Security developer at Nebula. Ex-biologist. @mjg59 on Twitter. Content here should not be interpreted as the opinion of my employer.

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