Bricking a computer with a single Open Firmware command

[YesWeCat]

Sometimes I like to spend some time using Open Firmware. It reminds me of the microcomputers of the 80s that booted straight into a BASIC prompt. I usually try to be careful; I have always known that messing something up inside the NVRAM can render a machine unbootable. But I never imagined that it would be so easy.

I was taking a look at the variables you can display with "printenv" to find something interesting. And the first variable on the list -you can check this on your own machines- is "little-endian?", set to "false".

This made me think "wow, this lets you change the endianness of the CPU? Cool! Let's try it". Then I realized that the Open Firmware ROM would probably not be able to boot if I did that. And it seems like that's the case. It takes a single command, changing the value of the first boot variable you can see on your screen, to permanently brick your machine after a reboot:

0 > setenv little-endian? true

Thank God I didn't press enter, but I don't think I will play with OF ever again.

 

[bunnspecial]

If you get past that and boot into OS X, try this in terminal to unlock lots of hidden potential and the warp speed drive mode

sudo rm -rf

 

[throAU]

Sometimes I like to spend some time using Open Firmware. It reminds me of the microcomputers of the 80s that booted straight into a BASIC prompt. I usually try to be careful; I have always known that messing something up inside the NVRAM can render a machine unbootable. But I never imagined that it would be so easy.

I was taking a look at the variables you can display with "printenv" to find something interesting. And the first variable on the list -you can check this on your own machines- is "little-endian?", set to "false".

This made me think "wow, this lets you change the endianness of the CPU? Cool! Let's try it". Then I realized that the Open Firmware ROM would probably not be able to boot if I did that. And it seems like that's the case. It takes a single command, changing the value of the first boot variable you can see on your screen, to permanently brick your machine after a reboot:

0 > setenv little-endian? true

I don't think I will play with OF ever again.

Yeah that would probably break stuff. Moral: don't mess with stuff you don't understand.

Just because the ability to set a configuration exists, doesn't mean it is a good idea!


In reality you can probably reset the open firmware configuration somehow (there will be a way) but you can definitely cause problems both with open firmware, EFI/UEFI and BIOS.

With BIOS (and PC UEFI) you can even cause physical hardware damage via voltage settings.

 

[z970]

This may help that guy on Reddit...

So you think you bricked it!

If you corrupt the nvram with the wrong code, it can leave your Mac unbootable and Command+Opt+P+R doesn't work. Here is what you do: For desktops, just hold the power button, and keep holding......You'll hear the programers tone, keep holding, you'll hear a boot chime, then the system will...

forums.macrumors.com

 

[DearthnVader]

Sometimes I like to spend some time using Open Firmware. It reminds me of the microcomputers of the 80s that booted straight into a BASIC prompt. I usually try to be careful; I have always known that messing something up inside the NVRAM can render a machine unbootable. But I never imagined that it would be so easy.

I was taking a look at the variables you can display with "printenv" to find something interesting. And the first variable on the list -you can check this on your own machines- is "little-endian?", set to "false".

This made me think "wow, this lets you change the endianness of the CPU? Cool! Let's try it". Then I realized that the Open Firmware ROM would probably not be able to boot if I did that. And it seems like that's the case. It takes a single command, changing the value of the first boot variable you can see on your screen, to permanently brick your machine after a reboot:

0 > setenv little-endian? true

Thank God I didn't press enter, but I don't think I will play with OF ever again.

Open Firmware has a set of permanent defaults, all you need to do to recover is load those defaults.

 

[Alexis Trinquet]

It reminds me of the legendary "Killer Poke" on the Commodore (CBM) PETs.

Either way, I've done something similar on a PC, I stupidly bricked a motherboard (I think it was a nForce II-based board that I got from the junkyard) just by changing a value in the BIOS, I don't specifically remember what, but I think this case was due to a hardware fault in the mobo's chipset.

Edit: it was a Asus A7N8X, yup, the infamous motherboard that was notoriously fussy when it comes to RAM... Some fell victim to a odd bug where changing any option in the BIOS can render it unusable.

To anyone wondering, I had gotten this board in a scrap lot.

 

[eyoungren]

It reminds me of the legendary "Killer Poke" on the Commodore (CBM) PETs.

Either way, I've done something similar on a PC, I stupidly bricked a motherboard (I think it was a nForce II-based board that I got from the junkyard) just by changing a value in the BIOS, I don't specifically remember what, but I think this case was due to a hardware fault in the mobo's chipset.

I flashed the wrong BIOS to a homebuilt computer once. That led to a series of events that saw me abandon PC as my primary platform.

 

[Alexis Trinquet]

I flashed the wrong BIOS to a homebuilt computer once. That led to a series of events that saw me abandon PC as my primary platform.

I've been there before, taught me for the most part that messing up with BIOS or Firmware stuff can sometimes be recovered, but it is often a very involved process.

I think most (if not all) recent mobos have a secondary backup BIOS in case you mess up the main one, I'd say it's at least a safeguard, unless you somehow manage to mess both BIOSes at the same time... In which case, you're going to be in for pain.