"Intel SGX is essentially a new mode of execution on the CPU, a new memory protection semantic, plus a couple of new instructions to manage this all. So, you create an enclave by filling its protected pages with desired code, then you lock it down, measure the code there, and if everything's fine, you ask the processor to start executing the code inside the enclave. Since now on, no entity, including the kernel (ring 0) or hypervisor (ring “-1”), or SMM (ring “-2”) or AMT (ring “-3”), has no right to read nor write the memory pages belonging to the enclave."
http://theinvisiblethings.blogspot.com/2013/08/thoughts-on-i...
http://theinvisiblethings.blogspot.com/2013/09/thoughts-on-i...
".. the processor automatically encrypts the content of SGX-protected memory pages whenever it leaves the processor caches and is stored in DRAM. In other words the code and data used by SGX enclaves never leave the processor in plaintext."
"..once the key is obtained, it is available only within the SGX enclave. It cannot be found in DRAM or on the memory bus, even if the user had access to expensive DRAM emulators or bus sniffers. And the key cannot also be mishandled by the code that runs in the SGX enclave, because remote attestation also proved that the loader code has not been modified.."
Hypervisors aren't just for virtualizing servers, you can use them for all sorts of things, like intercepting system calls.