On 2/2/21 2:33 PM, Sean Christopherson wrote:

quoted

Do we need to restrict normal KVM host kernel access to EPC (i.e. via
__kvm_map_gfn() and friends)? As best I can tell the exact behavior of
this kind of access is undefined. The concern would be if any HW ever
treated it as an error, the guest could subject the host kernel to it.
Is it worth a check in those?

I don't think so.  The SDM does state that the exact behavior is uArch specific,
but it also explicitly states that the access will be altered, which IMO doesn't
leave any wiggle room for a future CPU to fault instead of using some form of
abort semantics.

  Attempts to execute, read, or write to linear addresses mapped to EPC pages
  when not inside an enclave will result in the processor altering the access to
  preserve the confidentiality and integrity of the enclave. The exact behavior
  may be different between implementations.

I seem to remember much stronger language in the SDM about this.  I've
always thought of SGX as a big unrecoverable machine-check party waiting
to happen.

I'll ask around internally at Intel and see what folks say.  Basically,
should we be afraid of a big bad EPC access?