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SubjectRe: [PATCH v1 00/15] Add support for Nitro Enclaves

On 25/04/2020 18:25, Liran Alon wrote:
> On 23/04/2020 16:19, Paraschiv, Andra-Irina wrote:
>> The memory and CPUs are carved out of the primary VM, they are
>> dedicated for the enclave. The Nitro hypervisor running on the host
>> ensures memory and CPU isolation between the primary VM and the
>> enclave VM.
> I hope you properly take into consideration Hyper-Threading
> speculative side-channel vulnerabilities here.
> i.e. Usually cloud providers designate each CPU core to be assigned to
> run only vCPUs of specific guest. To avoid sharing a single CPU core
> between multiple guests.
> To handle this properly, you need to use some kind of core-scheduling
> mechanism (Such that each CPU core either runs only vCPUs of enclave
> or only vCPUs of primary VM at any given point in time).
> In addition, can you elaborate more on how the enclave memory is
> carved out of the primary VM?
> Does this involve performing a memory hot-unplug operation from
> primary VM or just unmap enclave-assigned guest physical pages from
> primary VM's SLAT (EPT/NPT) and map them now only in enclave's SLAT?

Correct, we take into consideration the HT setup. The enclave gets
dedicated physical cores. The primary VM and the enclave VM don't run on
CPU siblings of a physical core.

Regarding the memory carve out, the logic includes page table entries

IIRC, memory hot-unplug can be used for the memory blocks that were
previously hot-plugged.

>> Let me know if further clarifications are needed.
> I don't quite understand why Enclave VM needs to be
> provisioned/teardown during primary VM's runtime.
> For example, an alternative could have been to just provision both
> primary VM and Enclave VM on primary VM startup.
> Then, wait for primary VM to setup a communication channel with
> Enclave VM (E.g. via virtio-vsock).
> Then, primary VM is free to request Enclave VM to perform various
> tasks when required on the isolated environment.
> Such setup will mimic a common Enclave setup. Such as Microsoft
> Windows VBS EPT-based Enclaves (That all runs on VTL1). It is also
> similar to TEEs running on ARM TrustZone.
> i.e. In my alternative proposed solution, the Enclave VM is similar to
> VTL1/TrustZone.
> It will also avoid requiring introducing a new PCI device and driver.

True, this can be another option, to provision the primary VM and the
enclave VM at launch time.

In the proposed setup, the primary VM starts with the initial allocated
resources (memory, CPUs). The launch path of the enclave VM, as it's
spawned on the same host, is done via the ioctl interface - PCI device -
host hypervisor path. Short-running or long-running enclave can be
bootstrapped during primary VM lifetime. Depending on the use case, a
custom set of resources (memory and CPUs) is set for an enclave and then
given back when the enclave is terminated; these resources can be used
for another enclave spawned later on or the primary VM tasks.


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