[U-Boot] Disable command at runtime

[Wolfgang Denk]

Dear Petr,

In message <9c257c71-97b6-a83e-3d9d-e3a8459fc080 at elnico.cz> you wrote:
> 
> Anyway, at least a user feedback / feature request... I believe it would 
> be useful for many users to have a manufacturing mode, which they would 
> escape permanently by e.g. executing some command. In normal mode, some 
> commands would be disabled. Logic would be similar to 
> CONFIG_OVERWRITE_ETHADDR_ONCE.

How could that ever be "safe" - in the sense of protecting against an
attacker?  How could you perform such a "switch" between modes?  By
setting some bit somewhere.  And it has to be in some persistent
storage.  And the source code of your image is available to the
public.  What should prevent an attacker from undoing your bit
setting and switching back to "full" mode?

U-Boot is a boot loader, not a high security environment.  If you
grand somebody access to the U-Boot command line interface, he owns
the system.  If not directly, so by just pulling a few simple tricks.

Best regards,

Wolfgang Denk

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