| ====================================== | |
| Secure Encrypted Virtualization (SEV) | |
| ====================================== | |
| Overview | |
| ======== | |
| Secure Encrypted Virtualization (SEV) is a feature found on AMD processors. | |
| SEV is an extension to the AMD-V architecture which supports running | |
| virtual machines (VMs) under the control of a hypervisor. When enabled, | |
| the memory contents of a VM will be transparently encrypted with a key | |
| unique to that VM. | |
| The hypervisor can determine the SEV support through the CPUID | |
| instruction. The CPUID function 0x8000001f reports information related | |
| to SEV:: | |
| 0x8000001f[eax]: | |
| Bit[1] indicates support for SEV | |
| ... | |
| [ecx]: | |
| Bits[31:0] Number of encrypted guests supported simultaneously | |
| If support for SEV is present, MSR 0xc001_0010 (MSR_K8_SYSCFG) and MSR 0xc001_0015 | |
| (MSR_K7_HWCR) can be used to determine if it can be enabled:: | |
| 0xc001_0010: | |
| Bit[23] 1 = memory encryption can be enabled | |
| 0 = memory encryption can not be enabled | |
| 0xc001_0015: | |
| Bit[0] 1 = memory encryption can be enabled | |
| 0 = memory encryption can not be enabled | |
| When SEV support is available, it can be enabled in a specific VM by | |
| setting the SEV bit before executing VMRUN.:: | |
| VMCB[0x90]: | |
| Bit[1] 1 = SEV is enabled | |
| 0 = SEV is disabled | |
| SEV hardware uses ASIDs to associate a memory encryption key with a VM. | |
| Hence, the ASID for the SEV-enabled guests must be from 1 to a maximum value | |
| defined in the CPUID 0x8000001f[ecx] field. | |
| SEV Key Management | |
| ================== | |
| The SEV guest key management is handled by a separate processor called the AMD | |
| Secure Processor (AMD-SP). Firmware running inside the AMD-SP provides a secure | |
| key management interface to perform common hypervisor activities such as | |
| encrypting bootstrap code, snapshot, migrating and debugging the guest. For more | |
| information, see the SEV Key Management spec [api-spec]_ | |
| KVM implements the following commands to support common lifecycle events of SEV | |
| guests, such as launching, running, snapshotting, migrating and decommissioning. | |
| 1. KVM_SEV_INIT | |
| --------------- | |
| The KVM_SEV_INIT command is used by the hypervisor to initialize the SEV platform | |
| context. In a typical workflow, this command should be the first command issued. | |
| Returns: 0 on success, -negative on error | |
| 2. KVM_SEV_LAUNCH_START | |
| ----------------------- | |
| The KVM_SEV_LAUNCH_START command is used for creating the memory encryption | |
| context. To create the encryption context, user must provide a guest policy, | |
| the owner's public Diffie-Hellman (PDH) key and session information. | |
| Parameters: struct kvm_sev_launch_start (in/out) | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_launch_start { | |
| __u32 handle; /* if zero then firmware creates a new handle */ | |
| __u32 policy; /* guest's policy */ | |
| __u64 dh_uaddr; /* userspace address pointing to the guest owner's PDH key */ | |
| __u32 dh_len; | |
| __u64 session_addr; /* userspace address which points to the guest session information */ | |
| __u32 session_len; | |
| }; | |
| On success, the 'handle' field contains a new handle and on error, a negative value. | |
| For more details, see SEV spec Section 6.2. | |
| 3. KVM_SEV_LAUNCH_UPDATE_DATA | |
| ----------------------------- | |
| The KVM_SEV_LAUNCH_UPDATE_DATA is used for encrypting a memory region. It also | |
| calculates a measurement of the memory contents. The 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. | |
| Parameters (in): struct kvm_sev_launch_update_data | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_launch_update { | |
| __u64 uaddr; /* userspace address to be encrypted (must be 16-byte aligned) */ | |
| __u32 len; /* length of the data to be encrypted (must be 16-byte aligned) */ | |
| }; | |
| For more details, see SEV spec Section 6.3. | |
| 4. KVM_SEV_LAUNCH_MEASURE | |
| ------------------------- | |
| The KVM_SEV_LAUNCH_MEASURE command is used to retrieve the measurement of the | |
| data encrypted by the KVM_SEV_LAUNCH_UPDATE_DATA command. The guest owner may | |
| wait to provide the guest with confidential information until it can verify the | |
| measurement. Since the guest owner knows the initial contents of the guest at | |
| boot, the measurement can be verified by comparing it to what the guest owner | |
| expects. | |
| Parameters (in): struct kvm_sev_launch_measure | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_launch_measure { | |
| __u64 uaddr; /* where to copy the measurement */ | |
| __u32 len; /* length of measurement blob */ | |
| }; | |
| For more details on the measurement verification flow, see SEV spec Section 6.4. | |
| 5. KVM_SEV_LAUNCH_FINISH | |
| ------------------------ | |
| After completion of the launch flow, the KVM_SEV_LAUNCH_FINISH command can be | |
| issued to make the guest ready for the execution. | |
| Returns: 0 on success, -negative on error | |
| 6. KVM_SEV_GUEST_STATUS | |
| ----------------------- | |
| The KVM_SEV_GUEST_STATUS command is used to retrieve status information about a | |
| SEV-enabled guest. | |
| Parameters (out): struct kvm_sev_guest_status | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_guest_status { | |
| __u32 handle; /* guest handle */ | |
| __u32 policy; /* guest policy */ | |
| __u8 state; /* guest state (see enum below) */ | |
| }; | |
| SEV guest state: | |
| :: | |
| enum { | |
| SEV_STATE_INVALID = 0; | |
| SEV_STATE_LAUNCHING, /* guest is currently being launched */ | |
| SEV_STATE_SECRET, /* guest is being launched and ready to accept the ciphertext data */ | |
| SEV_STATE_RUNNING, /* guest is fully launched and running */ | |
| SEV_STATE_RECEIVING, /* guest is being migrated in from another SEV machine */ | |
| SEV_STATE_SENDING /* guest is getting migrated out to another SEV machine */ | |
| }; | |
| 7. KVM_SEV_DBG_DECRYPT | |
| ---------------------- | |
| The KVM_SEV_DEBUG_DECRYPT command can be used by the hypervisor to request the | |
| firmware to decrypt the data at the given memory region. | |
| Parameters (in): struct kvm_sev_dbg | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_dbg { | |
| __u64 src_uaddr; /* userspace address of data to decrypt */ | |
| __u64 dst_uaddr; /* userspace address of destination */ | |
| __u32 len; /* length of memory region to decrypt */ | |
| }; | |
| The command returns an error if the guest policy does not allow debugging. | |
| 8. KVM_SEV_DBG_ENCRYPT | |
| ---------------------- | |
| The KVM_SEV_DEBUG_ENCRYPT command can be used by the hypervisor to request the | |
| firmware to encrypt the data at the given memory region. | |
| Parameters (in): struct kvm_sev_dbg | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_dbg { | |
| __u64 src_uaddr; /* userspace address of data to encrypt */ | |
| __u64 dst_uaddr; /* userspace address of destination */ | |
| __u32 len; /* length of memory region to encrypt */ | |
| }; | |
| The command returns an error if the guest policy does not allow debugging. | |
| 9. KVM_SEV_LAUNCH_SECRET | |
| ------------------------ | |
| The KVM_SEV_LAUNCH_SECRET command can be used by the hypervisor to inject secret | |
| data after the measurement has been validated by the guest owner. | |
| Parameters (in): struct kvm_sev_launch_secret | |
| Returns: 0 on success, -negative on error | |
| :: | |
| struct kvm_sev_launch_secret { | |
| __u64 hdr_uaddr; /* userspace address containing the packet header */ | |
| __u32 hdr_len; | |
| __u64 guest_uaddr; /* the guest memory region where the secret should be injected */ | |
| __u32 guest_len; | |
| __u64 trans_uaddr; /* the hypervisor memory region which contains the secret */ | |
| __u32 trans_len; | |
| }; | |
| References | |
| ========== | |
| See [white-paper]_, [api-spec]_, [amd-apm]_ and [kvm-forum]_ for more info. | |
| .. [white-paper] http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf | |
| .. [api-spec] http://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf | |
| .. [amd-apm] http://support.amd.com/TechDocs/24593.pdf (section 15.34) | |
| .. [kvm-forum] http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf |