Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 ====================================== 2 Secure Encrypted Virtualization (SEV) 3 ====================================== 4 5 Overview 6 ======== 7 8 Secure Encrypted Virtualization (SEV) is a feature found on AMD processors. 9 10 SEV is an extension to the AMD-V architecture which supports running 11 virtual machines (VMs) under the control of a hypervisor. When enabled, 12 the memory contents of a VM will be transparently encrypted with a key 13 unique to that VM. 14 15 The hypervisor can determine the SEV support through the CPUID 16 instruction. The CPUID function 0x8000001f reports information related 17 to SEV:: 18 19 0x8000001f[eax]: 20 Bit[1] indicates support for SEV 21 ... 22 [ecx]: 23 Bits[31:0] Number of encrypted guests supported simultaneously 24 25 If support for SEV is present, MSR 0xc001_0010 (MSR_K8_SYSCFG) and MSR 0xc001_0015 26 (MSR_K7_HWCR) can be used to determine if it can be enabled:: 27 28 0xc001_0010: 29 Bit[23] 1 = memory encryption can be enabled 30 0 = memory encryption can not be enabled 31 32 0xc001_0015: 33 Bit[0] 1 = memory encryption can be enabled 34 0 = memory encryption can not be enabled 35 36 When SEV support is available, it can be enabled in a specific VM by 37 setting the SEV bit before executing VMRUN.:: 38 39 VMCB[0x90]: 40 Bit[1] 1 = SEV is enabled 41 0 = SEV is disabled 42 43 SEV hardware uses ASIDs to associate a memory encryption key with a VM. 44 Hence, the ASID for the SEV-enabled guests must be from 1 to a maximum value 45 defined in the CPUID 0x8000001f[ecx] field. 46 47 SEV Key Management 48 ================== 49 50 The SEV guest key management is handled by a separate processor called the AMD 51 Secure Processor (AMD-SP). Firmware running inside the AMD-SP provides a secure 52 key management interface to perform common hypervisor activities such as 53 encrypting bootstrap code, snapshot, migrating and debugging the guest. For more 54 information, see the SEV Key Management spec [api-spec]_ 55 56 KVM implements the following commands to support common lifecycle events of SEV 57 guests, such as launching, running, snapshotting, migrating and decommissioning. 58 59 1. KVM_SEV_INIT 60 --------------- 61 62 The KVM_SEV_INIT command is used by the hypervisor to initialize the SEV platform 63 context. In a typical workflow, this command should be the first command issued. 64 65 Returns: 0 on success, -negative on error 66 67 2. KVM_SEV_LAUNCH_START 68 ----------------------- 69 70 The KVM_SEV_LAUNCH_START command is used for creating the memory encryption 71 context. To create the encryption context, user must provide a guest policy, 72 the owner's public Diffie-Hellman (PDH) key and session information. 73 74 Parameters: struct kvm_sev_launch_start (in/out) 75 76 Returns: 0 on success, -negative on error 77 78 :: 79 80 struct kvm_sev_launch_start { 81 __u32 handle; /* if zero then firmware creates a new handle */ 82 __u32 policy; /* guest's policy */ 83 84 __u64 dh_uaddr; /* userspace address pointing to the guest owner's PDH key */ 85 __u32 dh_len; 86 87 __u64 session_addr; /* userspace address which points to the guest session information */ 88 __u32 session_len; 89 }; 90 91 On success, the 'handle' field contains a new handle and on error, a negative value. 92 93 For more details, see SEV spec Section 6.2. 94 95 3. KVM_SEV_LAUNCH_UPDATE_DATA 96 ----------------------------- 97 98 The KVM_SEV_LAUNCH_UPDATE_DATA is used for encrypting a memory region. It also 99 calculates a measurement of the memory contents. The measurement is a signature 100 of the memory contents that can be sent to the guest owner as an attestation 101 that the memory was encrypted correctly by the firmware. 102 103 Parameters (in): struct kvm_sev_launch_update_data 104 105 Returns: 0 on success, -negative on error 106 107 :: 108 109 struct kvm_sev_launch_update { 110 __u64 uaddr; /* userspace address to be encrypted (must be 16-byte aligned) */ 111 __u32 len; /* length of the data to be encrypted (must be 16-byte aligned) */ 112 }; 113 114 For more details, see SEV spec Section 6.3. 115 116 4. KVM_SEV_LAUNCH_MEASURE 117 ------------------------- 118 119 The KVM_SEV_LAUNCH_MEASURE command is used to retrieve the measurement of the 120 data encrypted by the KVM_SEV_LAUNCH_UPDATE_DATA command. The guest owner may 121 wait to provide the guest with confidential information until it can verify the 122 measurement. Since the guest owner knows the initial contents of the guest at 123 boot, the measurement can be verified by comparing it to what the guest owner 124 expects. 125 126 Parameters (in): struct kvm_sev_launch_measure 127 128 Returns: 0 on success, -negative on error 129 130 :: 131 132 struct kvm_sev_launch_measure { 133 __u64 uaddr; /* where to copy the measurement */ 134 __u32 len; /* length of measurement blob */ 135 }; 136 137 For more details on the measurement verification flow, see SEV spec Section 6.4. 138 139 5. KVM_SEV_LAUNCH_FINISH 140 ------------------------ 141 142 After completion of the launch flow, the KVM_SEV_LAUNCH_FINISH command can be 143 issued to make the guest ready for the execution. 144 145 Returns: 0 on success, -negative on error 146 147 6. KVM_SEV_GUEST_STATUS 148 ----------------------- 149 150 The KVM_SEV_GUEST_STATUS command is used to retrieve status information about a 151 SEV-enabled guest. 152 153 Parameters (out): struct kvm_sev_guest_status 154 155 Returns: 0 on success, -negative on error 156 157 :: 158 159 struct kvm_sev_guest_status { 160 __u32 handle; /* guest handle */ 161 __u32 policy; /* guest policy */ 162 __u8 state; /* guest state (see enum below) */ 163 }; 164 165 SEV guest state: 166 167 :: 168 169 enum { 170 SEV_STATE_INVALID = 0; 171 SEV_STATE_LAUNCHING, /* guest is currently being launched */ 172 SEV_STATE_SECRET, /* guest is being launched and ready to accept the ciphertext data */ 173 SEV_STATE_RUNNING, /* guest is fully launched and running */ 174 SEV_STATE_RECEIVING, /* guest is being migrated in from another SEV machine */ 175 SEV_STATE_SENDING /* guest is getting migrated out to another SEV machine */ 176 }; 177 178 7. KVM_SEV_DBG_DECRYPT 179 ---------------------- 180 181 The KVM_SEV_DEBUG_DECRYPT command can be used by the hypervisor to request the 182 firmware to decrypt the data at the given memory region. 183 184 Parameters (in): struct kvm_sev_dbg 185 186 Returns: 0 on success, -negative on error 187 188 :: 189 190 struct kvm_sev_dbg { 191 __u64 src_uaddr; /* userspace address of data to decrypt */ 192 __u64 dst_uaddr; /* userspace address of destination */ 193 __u32 len; /* length of memory region to decrypt */ 194 }; 195 196 The command returns an error if the guest policy does not allow debugging. 197 198 8. KVM_SEV_DBG_ENCRYPT 199 ---------------------- 200 201 The KVM_SEV_DEBUG_ENCRYPT command can be used by the hypervisor to request the 202 firmware to encrypt the data at the given memory region. 203 204 Parameters (in): struct kvm_sev_dbg 205 206 Returns: 0 on success, -negative on error 207 208 :: 209 210 struct kvm_sev_dbg { 211 __u64 src_uaddr; /* userspace address of data to encrypt */ 212 __u64 dst_uaddr; /* userspace address of destination */ 213 __u32 len; /* length of memory region to encrypt */ 214 }; 215 216 The command returns an error if the guest policy does not allow debugging. 217 218 9. KVM_SEV_LAUNCH_SECRET 219 ------------------------ 220 221 The KVM_SEV_LAUNCH_SECRET command can be used by the hypervisor to inject secret 222 data after the measurement has been validated by the guest owner. 223 224 Parameters (in): struct kvm_sev_launch_secret 225 226 Returns: 0 on success, -negative on error 227 228 :: 229 230 struct kvm_sev_launch_secret { 231 __u64 hdr_uaddr; /* userspace address containing the packet header */ 232 __u32 hdr_len; 233 234 __u64 guest_uaddr; /* the guest memory region where the secret should be injected */ 235 __u32 guest_len; 236 237 __u64 trans_uaddr; /* the hypervisor memory region which contains the secret */ 238 __u32 trans_len; 239 }; 240 241 References 242 ========== 243 244 .. [white-paper] http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf 245 .. [api-spec] http://support.amd.com/TechDocs/55766_SEV-KM%20API_Specification.pdf 246 .. [amd-apm] http://support.amd.com/TechDocs/24593.pdf (section 15.34) 247 .. [kvm-forum] http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf