6c8ebe30ea
Some upcoming POWER machines have a system called PEF (Protected
Execution Facility) which uses a small ultravisor to allow guests to
run in a way that they can't be eavesdropped by the hypervisor. The
effect is roughly similar to AMD SEV, although the mechanisms are
quite different.
Most of the work of this is done between the guest, KVM and the
ultravisor, with little need for involvement by qemu. However qemu
does need to tell KVM to allow secure VMs.
Because the availability of secure mode is a guest visible difference
which depends on having the right hardware and firmware, we don't
enable this by default. In order to run a secure guest you need to
create a "pef-guest" object and set the confidential-guest-support
property to point to it.
Note that this just *allows* secure guests, the architecture of PEF is
such that the guest still needs to talk to the ultravisor to enter
secure mode. Qemu has no direct way of knowing if the guest is in
secure mode, and certainly can't know until well after machine
creation time.
To start a PEF-capable guest, use the command line options:
-object pef-guest,id=pef0 -machine confidential-guest-support=pef0
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
47 lines
1.6 KiB
Plaintext
47 lines
1.6 KiB
Plaintext
Confidential Guest Support
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==========================
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Traditionally, hypervisors such as QEMU have complete access to a
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guest's memory and other state, meaning that a compromised hypervisor
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can compromise any of its guests. A number of platforms have added
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mechanisms in hardware and/or firmware which give guests at least some
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protection from a compromised hypervisor. This is obviously
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especially desirable for public cloud environments.
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These mechanisms have different names and different modes of
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operation, but are often referred to as Secure Guests or Confidential
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Guests. We use the term "Confidential Guest Support" to distinguish
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this from other aspects of guest security (such as security against
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attacks from other guests, or from network sources).
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Running a Confidential Guest
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----------------------------
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To run a confidential guest you need to add two command line parameters:
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1. Use "-object" to create a "confidential guest support" object. The
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type and parameters will vary with the specific mechanism to be
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used
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2. Set the "confidential-guest-support" machine parameter to the ID of
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the object from (1).
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Example (for AMD SEV)::
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qemu-system-x86_64 \
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<other parameters> \
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-machine ...,confidential-guest-support=sev0 \
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-object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1
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Supported mechanisms
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--------------------
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Currently supported confidential guest mechanisms are:
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AMD Secure Encrypted Virtualization (SEV)
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docs/amd-memory-encryption.txt
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POWER Protected Execution Facility (PEF)
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docs/papr-pef.txt
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Other mechanisms may be supported in future.
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