Re: Trusted process on an untrusted machine?

[pavel () SUSE CZ (Pavel Machek)]

Hi!

> Some of ways an attacker could bypass this protection:
> 4)  Kernel wars!  A SMP machine that boots an untrusted kernel.  Have
>     the APIC vector the attacking processor the timer interrupt then vector all
>     other interrupts to the 'good' proc.  The attacking proc then destroys
>     the MP configuration table so the 'good' proc doesnt know it is an MP
>     system.  The attacking proc then tries to take over the system after X
>     amount of time and steal the checksum/key.
>     [It has been a few months since I've looked at x86 SMP]
>     Solution:  There should be a LOCK pin on most processors that locks the
>                memory bus.  The kernel module can lock the bus and proceed to
>                zero out all memory not used by the good kernels page
> tables.

No. You can't assume you know about all memory. (And I think LOCK does
not work the way you imagine it). Rogue second cpu could be hiding in
videoram of PCI card, for example.

> 5)  Hardware bus snooping.  A PCI device on the memory bus to grab the
>     checksum/key then give the key to another malicious machine.
>     Solution:  ???

[This is not really usefull attack, but it can be well used to screw
you]

Remove heatsink from the cpu. Watch your "trusted" program do
single-bit errors from time to time. Have fun.

                                                                Pavel

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