Dear Wolfgang,
On 08/01/2016 10:05 PM, Wolfgang Denk wrote:
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?
If it was to be an irreversible switch, a reliable way might be to
effectively remove some parts of the program by overwriting them. Not
that I ever have done that, perhaps it's not that easy as I imagine, but
I believe it's possible.
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.
You are absolutely right, whoever has access to U-Boot, can easily
destroy the system. The main problem is perhaps in my understanding of
the concept. I'm always tempted to keep access to U-Boot "for future
sakes", but have not found a reliable way to deny the access to the
others. Is there a "correct approach"?
By the way, once I read in some conversation that bad security is no
security, so that's why U-Boot does not implement bad security. From my
point of view, bad security (e.g. password stored in env) is strong
enough to keep away the amateurs who just want to play with it and don't
really know they might destroy the system. Of course it does not secure
the system from the really evil attackers, but what does?
Best Regards,
Petr
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