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At least some s390 cpu models support "Protected Virtualization" (PV),
a mechanism to protect guests from eavesdropping by a compromised
hypervisor.
This is similar in function to other mechanisms like AMD's SEV and
POWER's PEF, which are controlled by the "confidential-guest-support"
machine option. s390 is a slightly special case, because we already
supported PV, simply by using a CPU model with the required feature
(S390_FEAT_UNPACK).
To integrate this with the option used by other platforms, we
implement the following compromise:
- When the confidential-guest-support option is set, s390 will
recognize it, verify that the CPU can support PV (failing if not)
and set virtio default options necessary for encrypted or protected
guests, as on other platforms. i.e. if confidential-guest-support
is set, we will either create a guest capable of entering PV mode,
or fail outright.
- If confidential-guest-support is not set, guests might still be
able to enter PV mode, if the CPU has the right model. This may be
a little surprising, but shouldn't actually be harmful.
To start a guest supporting Protected Virtualization using the new
option use the command line arguments:
-object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
50 lines
1.7 KiB
Plaintext
50 lines
1.7 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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s390x Protected Virtualization (PV)
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docs/system/s390x/protvirt.rst
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Other mechanisms may be supported in future.
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