Re: [PATCH 0/6] Intel Secure Guard Extensions

From: Andy Lutomirski
Date: Fri May 06 2016 - 12:22:23 EST

On Fri, May 6, 2016 at 4:23 AM, Jarkko Sakkinen
<jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> On Wed, Apr 27, 2016 at 10:18:05AM +0200, Ingo Molnar wrote:
>> * Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> > > What new syscalls would be needed for ssh to get all this support?
>> >
>> > This patchset or similar, plus some user code and an enclave to use.
>> >
>> > Sadly, on current CPUs, you also need Intel to bless the enclave. It looks like
>> > new CPUs might relax that requirement.
>> That looks like a fundamental technical limitation in my book - to an open source
>> user this is essentially a very similar capability as tboot: it only allows the
>> execution of externally blessed static binary blobs...
>> I don't think we can merge any of this upstream until it's clear that the hardware
>> owner running open-source user-space can also freely define/start his own secure
>> enclaves without having to sign the enclave with any external party. I.e.
>> self-signed enclaves should be fundamentally supported as well.
> Post Skylake we will have a set of MSRs for defining your own root of
> Andy had a concern that you could set root of trust multiple times,
> which could lead to potential attack scenarios. These MSRs are one-shot.
> ENCLS will fail if the launch control is locked. There's no possiblity
> to have a root of trust that is unlocked.

If this is actually true, can you ask the architecture folks to
clarify their manual.

The MSR description in table 35-2 says "Write permitted if
CPUID.(EAX=12H,ECX=0H): EAX[0]=1 && IA32_FEATURE_CONTROL[17] = 1 &&

39.1.4 says "If IA32_FEATURE_CONTROL is locked with bit 17 set,
IA32_SGXLEPUBKEYHASH MSRs are reconfigurable (writeable). If either
IA32_FEATURE_CONTROL is not locked or
bit 17 is clear, the MSRs are read only. By leaving these MSRs
writable, system SW or a VMM can support a plurality of Launch
Enclaves for hosting multiple execution environments."

This does not sound like one-shot to me. It sounds quite clear, in
fact, that it's *not* one-shot so a "plurality" of these things are