On Tue, Mar 28, 2017 at 2:40 AM, Vít Šesták
<[email protected]>
wrote:
> AFAIU, TPM is useful mostly for AEM. But AEM requires Intel TXT (which is
> missing even on some high-end CPUs). But TXT has various vulnerabilities. How
> much real protection can it offer? Is it worth the hassle (finding a laptop
> with both TPM and TXT and installing and using AEM)?
>
> To be honest, I don't know much about TPM/AEM/TXT.
Without directly answering your question (others in this community are
much better qualified to do that), I can offer the following:
See Joanna's "Intel x86 considered harmful" [1], particularly chapter
2 ("The BIOS and boot security").
Since publication of that paper we've seen increased availability of
Intel Boot Guard (moving the CRTM into the CPU rather than on mutable
flash potentially being executed before measurement) although whether
or not this really matters in practice remains unclear given the
typical long and complex chains of trust after that inherent to static
chains of trust to begin with.
Heads [2] is the best attempt I'm aware of to do something about the
"long chains of complex unauditable crap in your TCB for boot security
with a static root of trust" problem, and also did not exist at time
of publication of Joanna's paper.
[1]: https://blog.invisiblethings.org/papers/2015/x86_harmful.pdf
[2]: https://github.com/osresearch/heads
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