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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. | |
dc48bae0 BS |
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 | |
cf1754c2 | 245 | .. [api-spec] http://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf |
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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 |