The intention is to put the device setup into the boot ROM, so it can't (easily) change, but the working assumption is that one can

discard the privilege used to set up the device , or
be physically unsettable after it is initialized

I don't know the privilege primitives for intel/ARM, or if one needs a latch somewhere to make the device write-once: I'd love to talk to someone who does.

--dave

On 05/01/17 08:47 AM, Alvin Starr via talk wrote:

You need a write only device.

You could boot from a CD/DVD which is write only.

Or possibly an SD card that has the write-lock enabled.

If the computer does not support an SD card you could use usb card reader to boot from.

Of course in the worst case situation someone smart enough could rewrite the BIOS and get around any boot device.

On 01/05/2017 08:38 AM, David Collier-Brown via talk wrote:
Who can talk about (intel or arm) boot? I'm looking at a problem that can be solved by setting up a device at boot time and not letting the OS have the privilege or perhaps the physical ability to change it...

--dave
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David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb@spamcop.net           |                      -- Mark Twain
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David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb@spamcop.net           |                      -- Mark Twain