1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ============================================== 3 ===================================================================
4 The Definitive SEV Guest API Documentation 4 The Definitive SEV Guest API Documentation
5 ============================================== 5 ===================================================================
6 6
7 1. General description 7 1. General description
8 ====================== 8 ======================
9 9
10 The SEV API is a set of ioctls that are used b 10 The SEV API is a set of ioctls that are used by the guest or hypervisor
11 to get or set a certain aspect of the SEV virt 11 to get or set a certain aspect of the SEV virtual machine. The ioctls belong
12 to the following classes: 12 to the following classes:
13 13
14 - Hypervisor ioctls: These query and set glob 14 - Hypervisor ioctls: These query and set global attributes which affect the
15 whole SEV firmware. These ioctl are used b 15 whole SEV firmware. These ioctl are used by platform provisioning tools.
16 16
17 - Guest ioctls: These query and set attribute 17 - Guest ioctls: These query and set attributes of the SEV virtual machine.
18 18
19 2. API description 19 2. API description
20 ================== 20 ==================
21 21
22 This section describes ioctls that is used for 22 This section describes ioctls that is used for querying the SEV guest report
23 from the SEV firmware. For each ioctl, the fol 23 from the SEV firmware. For each ioctl, the following information is provided
24 along with a description: 24 along with a description:
25 25
26 Technology: 26 Technology:
27 which SEV technology provides this ioctl 27 which SEV technology provides this ioctl. SEV, SEV-ES, SEV-SNP or all.
28 28
29 Type: 29 Type:
30 hypervisor or guest. The ioctl can be us 30 hypervisor or guest. The ioctl can be used inside the guest or the
31 hypervisor. 31 hypervisor.
32 32
33 Parameters: 33 Parameters:
34 what parameters are accepted by the ioct 34 what parameters are accepted by the ioctl.
35 35
36 Returns: 36 Returns:
37 the return value. General error numbers 37 the return value. General error numbers (-ENOMEM, -EINVAL)
38 are not detailed, but errors with specif 38 are not detailed, but errors with specific meanings are.
39 39
40 The guest ioctl should be issued on a file des !! 40 The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
41 device. The ioctl accepts struct snp_user_gue !! 41 The ioctl accepts struct snp_user_guest_request. The input and output structure is
42 output structure is specified through the req_ !! 42 specified through the req_data and resp_data field respectively. If the ioctl fails
43 respectively. If the ioctl fails to execute du !! 43 to execute due to a firmware error, then fw_err code will be set otherwise the
44 the fw_error code will be set, otherwise fw_er !! 44 fw_err will be set to 0x00000000000000ff.
45 45
46 The firmware checks that the message sequence 46 The firmware checks that the message sequence counter is one greater than
47 the guests message sequence counter. If guest 47 the guests message sequence counter. If guest driver fails to increment message
48 counter (e.g. counter overflow), then -EIO wil 48 counter (e.g. counter overflow), then -EIO will be returned.
49 49
50 :: 50 ::
51 51
52 struct snp_guest_request_ioctl { 52 struct snp_guest_request_ioctl {
53 /* Message version number */ 53 /* Message version number */
54 __u32 msg_version; 54 __u32 msg_version;
55 55
56 /* Request and response struct 56 /* Request and response structure address */
57 __u64 req_data; 57 __u64 req_data;
58 __u64 resp_data; 58 __u64 resp_data;
59 59
60 /* bits[63:32]: VMM error code !! 60 /* firmware error code on failure (see psp-sev.h) */
61 union { !! 61 __u64 fw_err;
62 __u64 exitinfo2; <<
63 struct { <<
64 __u32 fw_error <<
65 __u32 vmm_erro <<
66 }; <<
67 }; <<
68 }; 62 };
69 63
70 The host ioctls are issued to a file descripto <<
71 The ioctl accepts the command ID/input structu <<
72 <<
73 :: <<
74 <<
75 struct sev_issue_cmd { <<
76 /* Command ID */ <<
77 __u32 cmd; <<
78 <<
79 /* Command request structure * <<
80 __u64 data; <<
81 <<
82 /* Firmware error code on fail <<
83 __u32 error; <<
84 }; <<
85 <<
86 <<
87 2.1 SNP_GET_REPORT 64 2.1 SNP_GET_REPORT
88 ------------------ 65 ------------------
89 66
90 :Technology: sev-snp 67 :Technology: sev-snp
91 :Type: guest ioctl 68 :Type: guest ioctl
92 :Parameters (in): struct snp_report_req 69 :Parameters (in): struct snp_report_req
93 :Returns (out): struct snp_report_resp on succ 70 :Returns (out): struct snp_report_resp on success, -negative on error
94 71
95 The SNP_GET_REPORT ioctl can be used to query 72 The SNP_GET_REPORT ioctl can be used to query the attestation report from the
96 SEV-SNP firmware. The ioctl uses the SNP_GUEST 73 SEV-SNP firmware. The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command
97 provided by the SEV-SNP firmware to query the 74 provided by the SEV-SNP firmware to query the attestation report.
98 75
99 On success, the snp_report_resp.data will cont 76 On success, the snp_report_resp.data will contains the report. The report
100 contain the format described in the SEV-SNP sp 77 contain the format described in the SEV-SNP specification. See the SEV-SNP
101 specification for further details. 78 specification for further details.
102 79
103 2.2 SNP_GET_DERIVED_KEY 80 2.2 SNP_GET_DERIVED_KEY
104 ----------------------- 81 -----------------------
105 :Technology: sev-snp 82 :Technology: sev-snp
106 :Type: guest ioctl 83 :Type: guest ioctl
107 :Parameters (in): struct snp_derived_key_req 84 :Parameters (in): struct snp_derived_key_req
108 :Returns (out): struct snp_derived_key_resp on 85 :Returns (out): struct snp_derived_key_resp on success, -negative on error
109 86
110 The SNP_GET_DERIVED_KEY ioctl can be used to g 87 The SNP_GET_DERIVED_KEY ioctl can be used to get a key derive from a root key.
111 The derived key can be used by the guest for a 88 The derived key can be used by the guest for any purpose, such as sealing keys
112 or communicating with external entities. 89 or communicating with external entities.
113 90
114 The ioctl uses the SNP_GUEST_REQUEST (MSG_KEY_ 91 The ioctl uses the SNP_GUEST_REQUEST (MSG_KEY_REQ) command provided by the
115 SEV-SNP firmware to derive the key. See SEV-SN 92 SEV-SNP firmware to derive the key. See SEV-SNP specification for further details
116 on the various fields passed in the key deriva 93 on the various fields passed in the key derivation request.
117 94
118 On success, the snp_derived_key_resp.data cont 95 On success, the snp_derived_key_resp.data contains the derived key value. See
119 the SEV-SNP specification for further details. 96 the SEV-SNP specification for further details.
120 97
121 98
122 2.3 SNP_GET_EXT_REPORT 99 2.3 SNP_GET_EXT_REPORT
123 ---------------------- 100 ----------------------
124 :Technology: sev-snp 101 :Technology: sev-snp
125 :Type: guest ioctl 102 :Type: guest ioctl
126 :Parameters (in/out): struct snp_ext_report_re 103 :Parameters (in/out): struct snp_ext_report_req
127 :Returns (out): struct snp_report_resp on succ 104 :Returns (out): struct snp_report_resp on success, -negative on error
128 105
129 The SNP_GET_EXT_REPORT ioctl is similar to the 106 The SNP_GET_EXT_REPORT ioctl is similar to the SNP_GET_REPORT. The difference is
130 related to the additional certificate data tha 107 related to the additional certificate data that is returned with the report.
131 The certificate data returned is being provide 108 The certificate data returned is being provided by the hypervisor through the
132 SNP_SET_EXT_CONFIG. 109 SNP_SET_EXT_CONFIG.
133 110
134 The ioctl uses the SNP_GUEST_REQUEST (MSG_REPO 111 The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command provided by the SEV-SNP
135 firmware to get the attestation report. 112 firmware to get the attestation report.
136 113
137 On success, the snp_ext_report_resp.data will 114 On success, the snp_ext_report_resp.data will contain the attestation report
138 and snp_ext_report_req.certs_address will cont 115 and snp_ext_report_req.certs_address will contain the certificate blob. If the
139 length of the blob is smaller than expected th 116 length of the blob is smaller than expected then snp_ext_report_req.certs_len will
140 be updated with the expected value. 117 be updated with the expected value.
141 118
142 See GHCB specification for further detail on h 119 See GHCB specification for further detail on how to parse the certificate blob.
143 120
144 2.4 SNP_PLATFORM_STATUS <<
145 ----------------------- <<
146 :Technology: sev-snp <<
147 :Type: hypervisor ioctl cmd <<
148 :Parameters (out): struct sev_user_data_snp_st <<
149 :Returns (out): 0 on success, -negative on err <<
150 <<
151 The SNP_PLATFORM_STATUS command is used to que <<
152 status includes API major, minor version and m <<
153 specification for further details. <<
154 <<
155 2.5 SNP_COMMIT <<
156 -------------- <<
157 :Technology: sev-snp <<
158 :Type: hypervisor ioctl cmd <<
159 :Returns (out): 0 on success, -negative on err <<
160 <<
161 SNP_COMMIT is used to commit the currently ins <<
162 SEV-SNP firmware SNP_COMMIT command. This prev <<
163 committed firmware version. This will also upd <<
164 that of the currently installed firmware. <<
165 <<
166 2.6 SNP_SET_CONFIG <<
167 ------------------ <<
168 :Technology: sev-snp <<
169 :Type: hypervisor ioctl cmd <<
170 :Parameters (in): struct sev_user_data_snp_con <<
171 :Returns (out): 0 on success, -negative on err <<
172 <<
173 SNP_SET_CONFIG is used to set the system-wide <<
174 reported TCB version in the attestation report <<
175 to SNP_CONFIG command defined in the SEV-SNP s <<
176 the firmware parameters affected by this comma <<
177 SNP_PLATFORM_STATUS. <<
178 <<
179 2.7 SNP_VLEK_LOAD <<
180 ----------------- <<
181 :Technology: sev-snp <<
182 :Type: hypervisor ioctl cmd <<
183 :Parameters (in): struct sev_user_data_snp_vle <<
184 :Returns (out): 0 on success, -negative on err <<
185 <<
186 When requesting an attestation report a guest <<
187 it wants SNP firmware to sign the report using <<
188 Endorsement Key (VCEK), which is derived from <<
189 Versioned Loaded Endorsement Key (VLEK) which <<
190 Key Derivation Service (KDS) and derived from <<
191 enrolled cloud service providers. <<
192 <<
193 In the case of VLEK keys, the SNP_VLEK_LOAD SN <<
194 them into the system after obtaining them from <<
195 closely to the SNP_VLEK_LOAD firmware command <<
196 spec. <<
197 <<
198 3. SEV-SNP CPUID Enforcement 121 3. SEV-SNP CPUID Enforcement
199 ============================ 122 ============================
200 123
201 SEV-SNP guests can access a special page that 124 SEV-SNP guests can access a special page that contains a table of CPUID values
202 that have been validated by the PSP as part of 125 that have been validated by the PSP as part of the SNP_LAUNCH_UPDATE firmware
203 command. It provides the following assurances 126 command. It provides the following assurances regarding the validity of CPUID
204 values: 127 values:
205 128
206 - Its address is obtained via bootloader/firm 129 - Its address is obtained via bootloader/firmware (via CC blob), and those
207 binaries will be measured as part of the SE 130 binaries will be measured as part of the SEV-SNP attestation report.
208 - Its initial state will be encrypted/pvalida 131 - Its initial state will be encrypted/pvalidated, so attempts to modify
209 it during run-time will result in garbage b 132 it during run-time will result in garbage being written, or #VC exceptions
210 being generated due to changes in validatio 133 being generated due to changes in validation state if the hypervisor tries
211 to swap the backing page. 134 to swap the backing page.
212 - Attempts to bypass PSP checks by the hyperv 135 - Attempts to bypass PSP checks by the hypervisor by using a normal page, or
213 a non-CPUID encrypted page will change the 136 a non-CPUID encrypted page will change the measurement provided by the
214 SEV-SNP attestation report. 137 SEV-SNP attestation report.
215 - The CPUID page contents are *not* measured, 138 - The CPUID page contents are *not* measured, but attempts to modify the
216 expected contents of a CPUID page as part o 139 expected contents of a CPUID page as part of guest initialization will be
217 gated by the PSP CPUID enforcement policy c 140 gated by the PSP CPUID enforcement policy checks performed on the page
218 during SNP_LAUNCH_UPDATE, and noticeable la 141 during SNP_LAUNCH_UPDATE, and noticeable later if the guest owner
219 implements their own checks of the CPUID va 142 implements their own checks of the CPUID values.
220 143
221 It is important to note that this last assuran 144 It is important to note that this last assurance is only useful if the kernel
222 has taken care to make use of the SEV-SNP CPUI 145 has taken care to make use of the SEV-SNP CPUID throughout all stages of boot.
223 Otherwise, guest owner attestation provides no 146 Otherwise, guest owner attestation provides no assurance that the kernel wasn't
224 fed incorrect values at some point during boot 147 fed incorrect values at some point during boot.
225 <<
226 4. SEV Guest Driver Communication Key <<
227 ===================================== <<
228 <<
229 Communication between an SEV guest and the SEV <<
230 Processor (ASP, aka PSP) is protected by a VM <<
231 (VMPCK). By default, the sev-guest driver uses <<
232 VM Privilege Level (VMPL) at which the guest i <<
233 wiped by the sev-guest driver (see the driver <<
234 wiped), a different key can be used by reloadi <<
235 specifying the desired key using the vmpck_id <<
236 148
237 149
238 Reference 150 Reference
239 --------- 151 ---------
240 152
241 SEV-SNP and GHCB specification: developer.amd. 153 SEV-SNP and GHCB specification: developer.amd.com/sev
242 154
243 The driver is based on SEV-SNP firmware spec 0 155 The driver is based on SEV-SNP firmware spec 0.9 and GHCB spec version 2.0.
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