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Samsung Laptop Bug Is Not Linux Specific
First time accepted submitter YurB writes "Matthew Garrett, a Linux kernel developer who was investigating the recent Linux-on-Samsung-in-UEFI-mode problem, has bricked a Samsung laptop using a test userspace program in Windows. The most fascinating part of the story is on what is actually causing the firmware boot failure: 'Unfortunately, it turns out that some Samsung laptops will fail to boot if too much of the [UEFI] variable storage space is used. We don't know what "too much" is yet, but writing a bunch of variables from Windows is enough to trigger it. I put some sample code here — it writes out 36 variables each containing a kilobyte of random data. I ran this as an administrator under Windows and then rebooted the system. It never came back.'"
I believe you misread the article. Taking Linux out of the equation still caused the problem. :P
I think the reason why it was most commonly found in Linux is that you can have several different variables to boot the system. Especially if you are one of those super custom freaks.
It needs to rewrite as: "Embrace a full test of the UEFI" or "Check storage limits on the UEFI"
Why they wouldn't put more storage on the UEFI, as cheap as it is, boggles my mind.
"That's right...I said it."
Removing the CMOS battery didn't recover this system, which is pretty much what I'd expect - UEFI variables are typically stored in the same hardware as the firmware itself, and unplugging batteries doesn't kill your firmware.
The system doesn't fail to boot. The system doesn't even complete its power-on self checks. The screen is never turned on. It never responds to keyboard input. It's bricked. This machine's not coming back to life without an SPI programmer.
UEFI is much more than secure-boot. There are a lot of "hacks" required right now to make BIOS work properly for modern scenerios. the 4 partition limit is a good example, we have to use "logical" partitions within a bigger physical partition to get around this bullshit at the moment, UEFI fixes that. It also adds a LOT of other functionality such as much more powerful configuration interfaces that can supply graphics (temperature meters, etc), handle mouse input and drive system speakers directly.
You can almost certainly re-program it using a JTAG interface... Samsung can do this at the factory if you return it to them. JTAG is not intended for consumer use, though. My old university had a JTAG probe and several adapters to interface with various hardware vendors proprietary interfaces - without this we would have had several multi-thousand dollar bricks in our hardware lab :)
I would hope that Samsung would have the decency to admit a flaw in their design and provide the reprogramming free of charge, but ...
Think of it this way - the PC boots the same way today as it did 30 years ago. The BIOS reads the first sector ot the first hard drive at a specific location in low memory and jumps there. Now, in most cases, that is a standard MBR loader - it reads the partition table (also embedded in the first sector - great design, eh?), the calculates where the next sector (the first sector of the partition) should be ont he disk. It calls the BIOS to load that into another location in RAM, then jumps into it. That one hopefully loads more of itself so it can then load the OS. All this happens in 16 bit real mode.
EFI boot allows the loader to reside in a special EFI storage partition, where it can find the OS loader, and then the OS loader can directly, instead of chain loading various sectors all over the place (and often having to have a bootstrap loader be the one to fit in 512 bytes, that loads the main part of the boot loader - think the nasty hack that is grub's stage 1/2/2.5/etc loader and think how much nicer it would be if the BIOS would just read it off the disk)
In fact, practically all PCs sold have an EFI/UEFI bootloader by default - Intel has been shipping them for many years now (prior to 2006 - when Apple introduced the Intel Macs, even - probably the first experience most people have with EFI). What's been happening is that the EFI loader has been calling into the BIOS emulation layer to perform the BIOS legacy boot.
Basically, its a more advanced bootloader because really, initializing hardware is getting more complex. Think stuff like USB for example - it requires a lot of high level integration in order to work, and stuff like EFI can make it much easier to do so because it's like a mini OS. Plus getting rid of the 512 byte loader limitation.
Finally, (U)EFI is a joint collaboration between Microsoft and Intel - Intel created several technologies, including the GPT (which is required if you want a >3TB drive to be useful and not truncated to 3TB - MBR is useless at this point - and important if you're running huge RAID arrays)., while using others from Microsoft (the on-disk EFI partition is... FAT32, and the binaries it loads are PE COFF exe's).