i386/sev: Introduce 'sev-snp-guest' object

SEV-SNP support relies on a different set of properties/state than the
existing 'sev-guest' object. This patch introduces the 'sev-snp-guest'
object, which can be used to configure an SEV-SNP guest. For example,
a default-configured SEV-SNP guest with no additional information
passed in for use with attestation:

  -object sev-snp-guest,id=sev0

or a fully-specified SEV-SNP guest where all spec-defined binary
blobs are passed in as base64-encoded strings:

  -object sev-snp-guest,id=sev0, \
    policy=0x30000, \
    init-flags=0, \
    id-block=YWFhYWFhYWFhYWFhYWFhCg==, \
    id-auth=CxHK/OKLkXGn/KpAC7Wl1FSiisWDbGTEKz..., \
    author-key-enabled=on, \
    host-data=LNkCWBRC5CcdGXirbNUV1OrsR28s..., \
    guest-visible-workarounds=AA==, \

See the QAPI schema updates included in this patch for more usage
details.

In some cases these blobs may be up to 4096 characters, but this is
generally well below the default limit for linux hosts where
command-line sizes are defined by the sysconf-configurable ARG_MAX
value, which defaults to 2097152 characters for Ubuntu hosts, for
example.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Acked-by: Markus Armbruster <armbru@redhat.com> (for QAPI schema)
Signed-off-by: Michael Roth <michael.roth@amd.com>
Co-developed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-8-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 68 insertions, 2 deletions

diff --git a/docs/system/i386/amd-memory-encryption.rst b/docs/system/i386/amd-memory-encryption.rst
index e9bc142bc1..748f5094ba 100644
--- a/docs/system/i386/amd-memory-encryption.rst
+++ b/docs/system/i386/amd-memory-encryption.rst
@@ -25,8 +25,8 @@ 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
----------
+Launching (SEV and SEV-ES)
+--------------------------
 
 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``,
@@ -161,6 +161,72 @@ The value of GCTX.LD is
 If kernel hashes are not used, or SEV-ES is disabled, use empty blobs for
 ``kernel_hashes_blob`` and ``vmsas_blob`` as needed.
 
+Launching (SEV-SNP)
+-------------------
+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:
+``SNP_LAUNCH_START``, ``SNP_LAUNCH_UPDATE``, and ``SNP_LAUNCH_FINISH``. These
+three commands communicate with SEV-SNP firmware to generate a fresh memory
+encryption key for the VM, encrypt the boot images for a successful launch. For
+more details on the SEV-SNP firmware interfaces used by these commands please
+see the SEV-SNP Firmware ABI.
+
+``SNP_LAUNCH_START`` is called first to create a cryptographic launch context
+within the firmware. To create this context, the guest owner must provide a
+guest policy and other parameters as described in the SEV-SNP firmware
+specification. The launch parameters should be specified as described in the
+QAPI schema for the sev-snp-guest object.
+
+The ``SNP_LAUNCH_START`` uses the following parameters, which can be configured
+by the corresponding parameters documented in the QAPI schema for the
+'sev-snp-guest' object.
+
++--------+-------+----------+-------------------------------------------------+
+| key                       | type  | default  | meaning                      |
++---------------------------+-------------------------------------------------+
+| policy                    | hex   | 0x30000  | a 64-bit guest policy        |
++---------------------------+-------------------------------------------------+
+| guest-visible-workarounds | string| 0        | 16-byte base64 encoded string|
+|                           |       |          | for guest OS visible         |
+|                           |       |          | workarounds.                 |
++---------------------------+-------------------------------------------------+
+
+``SNP_LAUNCH_UPDATE`` encrypts the memory region using the cryptographic context
+created via the ``SNP_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.
+
+``SNP_LAUNCH_FINISH`` finalizes the guest launch flow. Optionally, while
+finalizing the launch the firmware can perform checks on the launch digest
+computing through the ``SNP_LAUNCH_UPDATE``. To perform the check the user must
+supply the id block, authentication blob and host data that should be included
+in the attestation report. See the SEV-SNP spec for further details.
+
+The ``SNP_LAUNCH_FINISH`` uses the following parameters, which can be configured
+by the corresponding parameters documented in the QAPI schema for the
+'sev-snp-guest' object.
+
++--------------------+-------+----------+-------------------------------------+
+| key                | type  | default  | meaning                             |
++--------------------+-------+----------+-------------------------------------+
+| id-block           | string| none     | base64 encoded ID block             |
++--------------------+-------+----------+-------------------------------------+
+| id-auth            | string| none     | base64 encoded authentication       |
+|                    |       |          | information                         |
++--------------------+-------+----------+-------------------------------------+
+| author-key-enabled | bool  | 0        | auth block contains author key      |
++--------------------+-------+----------+-------------------------------------+
+| host_data          | string| none     | host provided data                  |
++--------------------+-------+----------+-------------------------------------+
+
+To launch a SEV-SNP guest (additional parameters are documented in the QAPI
+schema for the 'sev-snp-guest' object)::
+
+  # ${QEMU} \
+    -machine ...,confidential-guest-support=sev0 \
+    -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1
+
+
 Debugging
 ---------