From 61b7d7098cd53dd386939610d534f8bd79240881 Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Fri, 23 Apr 2021 15:08:18 -0500 Subject: [PATCH] docs: Add SEV-ES documentation to amd-memory-encryption.txt 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 Acked-by: Laszlo Ersek Reviewed-by: Connor Kuehl Message-Id: Signed-off-by: Eduardo Habkost --- docs/amd-memory-encryption.txt | 54 +++++++++++++++++++++++++++++----- 1 file changed, 47 insertions(+), 7 deletions(-) diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt index ed85159ea7..ffca382b5f 100644 --- a/docs/amd-memory-encryption.txt +++ b/docs/amd-memory-encryption.txt @@ -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