Confidential Guest Support

Traditionally, hypervisors such as QEMU have complete access to a guest’s memory and other state, meaning that a compromised hypervisor can compromise any of its guests. A number of platforms have added mechanisms in hardware and/or firmware which give guests at least some protection from a compromised hypervisor. This is obviously especially desirable for public cloud environments.

These mechanisms have different names and different modes of operation, but are often referred to as Secure Guests or Confidential Guests. We use the term “Confidential Guest Support” to distinguish this from other aspects of guest security (such as security against attacks from other guests, or from network sources).

Running a Confidential Guest

To run a confidential guest you need to add two command line parameters:

Use -object to create a “confidential guest support” object. The type and parameters will vary with the specific mechanism to be used
Set the confidential-guest-support machine parameter to the ID of the object from (1).

Example (for AMD SEV):

qemu-system-x86_64 \
    <other parameters> \
    -machine ...,confidential-guest-support=sev0 \
    -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1

Supported mechanisms

Currently supported confidential guest mechanisms are:

AMD Secure Encrypted Virtualization (SEV) (see AMD Secure Encrypted Virtualization (SEV))
POWER Protected Execution Facility (PEF) (see POWER (PAPR) Protected Execution Facility (PEF))
s390x Protected Virtualization (PV) (see Protected Virtualization on s390x)

Other mechanisms may be supported in future.