docs: rstfy confidential guest documentation

Also rstfy the documentation for AMD SEV, and link it.

The documentation for PEF had been merged into the pseries doc,
fix the reference.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220204161251.241877-1-cohuck@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/docs/system/i386/amd-memory-encryption.rst b/docs/system/i386/amd-memory-encryption.rst
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+AMD Secure Encrypted Virtualization (SEV)
+=========================================
+
+Secure Encrypted Virtualization (SEV) is a feature found on AMD processors.
+
+SEV is an extension to the AMD-V architecture which supports running encrypted
+virtual machines (VMs) under the control of KVM. Encrypted VMs have their pages
+(code and data) secured such that only the guest itself has access to the
+unencrypted version. Each encrypted VM is associated with a unique encryption
+key; if its data is accessed by a different entity using a different key the
+encrypted guests data will be incorrectly decrypted, leading to unintelligible
+data.
+
+Key management for this feature is handled by a separate processor known as the
+AMD secure processor (AMD-SP), which is present in AMD SOCs. Firmware running
+inside the AMD-SP provides commands to support a common VM lifecycle. This
+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
+``MEMORY_ENCRYPT_OP`` ioctl provides commands to encrypt the images: ``LAUNCH_START``,
+``LAUNCH_UPDATE_DATA``, ``LAUNCH_MEASURE`` and ``LAUNCH_FINISH``. These four commands
+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
+should be treated as a binary blob and must be passed as-is to the SEV firmware.
+
+The guest policy is passed as plaintext. A hypervisor may choose to read it,
+but should not modify it (any modification of the policy bits will result
+in bad measurement). The guest policy is a 4-byte data structure containing
+several flags that restricts what can be done on a running SEV guest.
+See KM Spec section 3 and 6.2 for more details.
+
+The guest policy can be provided via the ``policy`` property::
+
+  # ${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::
+
+  # ${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.
+
+The DH certificate and session blob can be provided via the ``dh-cert-file`` and
+``session-file`` properties::
+
+  # ${QEMU} \
+       sev-guest,id=sev0,dh-cert-file=<file1>,session-file=<file2>
+
+``LAUNCH_UPDATE_DATA`` encrypts the memory region using the cryptographic context
+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_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.
+
+See SEV KM API Spec ([SEVKM]_) 'Launching a guest' usage flow (Appendix A) for the
+complete flow chart.
+
+To launch a SEV guest::
+
+  # ${QEMU} \
+      -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
+the guest memory will return cipher text. If the guest policy allows debugging,
+then a hypervisor can use the DEBUG_DECRYPT and DEBUG_ENCRYPT commands to access
+the guest memory region for debug purposes.  This is not supported in QEMU yet.
+
+Snapshot/Restore
+----------------
+
+TODO
+
+Live Migration
+---------------
+
+TODO
+
+References
+----------
+
+`AMD Memory Encryption whitepaper
+<https://developer.amd.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf>`_
+
+.. [SEVKM] `Secure Encrypted Virtualization Key Management
+   <http://developer.amd.com/wordpress/media/2017/11/55766_SEV-KM-API_Specification.pdf>`_
+
+KVM Forum slides:
+
+* `AMD’s Virtualization Memory Encryption (2016)
+  <http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf>`_
+* `Extending Secure Encrypted Virtualization With SEV-ES (2018)
+  <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