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docs: Add SEV-ES documentation to amd-memory-encryption.txt

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Update the amd-memory-encryption.txt file with information about SEV-ES,
including how to launch an SEV-ES guest and some of the differences
between SEV and SEV-ES guests in regards to launching and measuring the
guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Message-Id: <fa1825a5eb0290eac4712cde75ba4c6829946eac.1619208498.git.thomas.lendacky@amd.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Tom Lendacky 2021-04-23 15:08:18 -05:00 committed by Eduardo Habkost
parent f538adeccf
commit 61b7d7098c
1 changed files with 47 additions and 7 deletions
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54
docs/amd-memory-encryption.txt
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@ -15,6 +15,13 @@ includes commands for launching, snapshotting, migrating and debugging the
encrypted guest. These SEV commands can be issued via KVM_MEMORY_ENCRYPT_OP
ioctls.
Secure Encrypted Virtualization - Encrypted State (SEV-ES) builds on the SEV
support to additionally protect the guest register state. In order to allow a
hypervisor to perform functions on behalf of a guest, there is architectural
support for notifying a guest's operating system when certain types of VMEXITs
are about to occur. This allows the guest to selectively share information with
the hypervisor to satisfy the requested function.
Launching
---------
Boot images (such as bios) must be encrypted before a guest can be booted. The
@ -24,6 +31,9 @@ together generate a fresh memory encryption key for the VM, encrypt the boot
images and provide a measurement than can be used as an attestation of a
successful launch.
For a SEV-ES guest, the LAUNCH_UPDATE_VMSA command is also used to encrypt the
guest register state, or VM save area (VMSA), for all of the guest vCPUs.
LAUNCH_START is called first to create a cryptographic launch context within
the firmware. To create this context, guest owner must provide a guest policy,
its public Diffie-Hellman key (PDH) and session parameters. These inputs
@ -40,6 +50,12 @@ The guest policy can be provided via the 'policy' property (see below)
# ${QEMU} \
sev-guest,id=sev0,policy=0x1...\
Setting the "SEV-ES required" policy bit (bit 2) will launch the guest as a
SEV-ES guest (see below)
# ${QEMU} \
sev-guest,id=sev0,policy=0x5...\
The guest owner provided DH certificate and session parameters will be used to
establish a cryptographic session with the guest owner to negotiate keys used
for the attestation.
@ -55,13 +71,19 @@ created via the LAUNCH_START command. If required, this command can be called
multiple times to encrypt different memory regions. The command also calculates
the measurement of the memory contents as it encrypts.
LAUNCH_MEASURE can be used to retrieve the measurement of encrypted memory.
This measurement is a signature of the memory contents that can be sent to the
guest owner as an attestation that the memory was encrypted correctly by the
firmware. The guest owner may wait to provide the guest confidential information
until it can verify the attestation measurement. Since the guest owner knows the
initial contents of the guest at boot, the attestation measurement can be
verified by comparing it to what the guest owner expects.
LAUNCH_UPDATE_VMSA encrypts all the vCPU VMSAs for a SEV-ES guest using the
cryptographic context created via the LAUNCH_START command. The command also
calculates the measurement of the VMSAs as it encrypts them.
LAUNCH_MEASURE can be used to retrieve the measurement of encrypted memory and,
for a SEV-ES guest, encrypted VMSAs. This measurement is a signature of the
memory contents and, for a SEV-ES guest, the VMSA contents, that can be sent
to the guest owner as an attestation that the memory and VMSAs were encrypted
correctly by the firmware. The guest owner may wait to provide the guest
confidential information until it can verify the attestation measurement.
Since the guest owner knows the initial contents of the guest at boot, the
attestation measurement can be verified by comparing it to what the guest owner
expects.
LAUNCH_FINISH finalizes the guest launch and destroys the cryptographic
context.
@ -75,6 +97,22 @@ To launch a SEV guest
-machine ...,confidential-guest-support=sev0 \
-object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1
To launch a SEV-ES guest
# ${QEMU} \
-machine ...,confidential-guest-support=sev0 \
-object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1,policy=0x5
An SEV-ES guest has some restrictions as compared to a SEV guest. Because the
guest register state is encrypted and cannot be updated by the VMM/hypervisor,
a SEV-ES guest:
- Does not support SMM - SMM support requires updating the guest register
state.
- Does not support reboot - a system reset requires updating the guest register
state.
- Requires in-kernel irqchip - the burden is placed on the hypervisor to
manage booting APs.
Debugging
-----------
Since the memory contents of a SEV guest are encrypted, hypervisor access to
@ -101,8 +139,10 @@ Secure Encrypted Virtualization Key Management:
KVM Forum slides:
http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf
https://www.linux-kvm.org/images/9/94/Extending-Secure-Encrypted-Virtualization-with-SEV-ES-Thomas-Lendacky-AMD.pdf
AMD64 Architecture Programmer's Manual:
http://support.amd.com/TechDocs/24593.pdf
SME is section 7.10
SEV is section 15.34
SEV-ES is section 15.35