From: Tom Lendacky <thomas.lenda...@amd.com>
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.lenda...@amd.com>
---
docs/amd-memory-encryption.txt | 45 ++++++++++++++++++++++++++++------
1 file changed, 37 insertions(+), 8 deletions(-)
diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt
index 145896aec7..795b990fab 100644
--- a/docs/amd-memory-encryption.txt
+++ b/docs/amd-memory-encryption.txt
@@ -12,18 +12,28 @@ The key management of this feature is handled by separate
processor known as
AMD secure processor (AMD-SP) which is present in AMD SOCs. Firmware running
inside the AMD-SP provide commands to support common VM lifecycle. This
includes commands for launching, snapshotting, migrating and debugging the
-encrypted guest. Those SEV command can be issued via KVM_MEMORY_ENCRYPT_OP
+encrypted guest. Those 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 guest can be booted.
-MEMORY_ENCRYPT_OP ioctl provides commands to encrypt the images :LAUNCH_START,
+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 the
successful launch.
+For an 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 provides guest policy,
its public Diffie-Hellman key (PDH) and session parameters. These inputs
@@ -40,31 +50,42 @@ 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 an
+SEV-ES guest (see below)
+
+# ${QEMU} \
+ sev-guest,id=sev0,policy=0x5...\
+
Guest owners 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 'dh-cert-file' and
-'session-file' property (see below
+'session-file' property (see below)
# ${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 LAUNCH_START command. If required, this command can be called
+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 command 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
+LAUNCH_UPDATE_VMSA encrypts all the vCPU VMSAs for an 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 an SEV-ES guest, encrypted VMSAs. This measurement is a signature of the
+memory contents and, for an 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 command finalizes the guest launch and destroy's the
cryptographic
+LAUNCH_FINISH command finalizes the guest launch and destroys the cryptographic
context.
See SEV KM API Spec [1] 'Launching a guest' usage flow (Appendix A) for the
@@ -76,6 +97,12 @@ 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
+
Debugging
-----------
Since memory contents of SEV guest is encrypted hence hypervisor access to the
@@ -102,8 +129,10 @@ 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
--
2.31.0
