The SNP_GET_DERIVED_KEY ioctl interface can be used by the SNP guest to ask the firmware to provide a key derived from a root key. The derived key may be used by the guest for any purposes it choose, such as a sealing key or communicating with the external entities. See SEV-SNP firmware spec for more information. Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx> --- Documentation/virt/coco/sevguest.rst | 18 ++++++++++ drivers/virt/coco/sevguest/sevguest.c | 48 +++++++++++++++++++++++++++ include/uapi/linux/sev-guest.h | 24 ++++++++++++++ 3 files changed, 90 insertions(+) diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst index 52d5915037ef..25446670d816 100644 --- a/Documentation/virt/coco/sevguest.rst +++ b/Documentation/virt/coco/sevguest.rst @@ -67,3 +67,21 @@ provided by the SEV-SNP firmware to query the attestation report. On success, the snp_report_resp.data will contains the report. The report format is described in the SEV-SNP specification. See the SEV-SNP specification for further details. + +2.2 SNP_GET_DERIVED_KEY +----------------------- +:Technology: sev-snp +:Type: guest ioctl +:Parameters (in): struct snp_derived_key_req +:Returns (out): struct snp_derived_key_req on success, -negative on error + +The SNP_GET_DERIVED_KEY ioctl can be used to get a key derive from a root key. +The derived key can be used by the guest for any purpose, such as sealing keys +or communicating with external entities. + +The ioctl uses the SNP_GUEST_REQUEST (MSG_KEY_REQ) command provided by the +SEV-SNP firmware to derive the key. See SEV-SNP specification for further details +on the various fileds passed in the key derivation request. + +On success, the snp_derived_key_resp.data will contains the derived key +value. diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c index f3f86f9b5b22..2f20db80490a 100644 --- a/drivers/virt/coco/sevguest/sevguest.c +++ b/drivers/virt/coco/sevguest/sevguest.c @@ -304,6 +304,50 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_user_guest_reque return rc; } +static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_user_guest_request *arg) +{ + struct snp_guest_crypto *crypto = snp_dev->crypto; + struct snp_derived_key_resp *resp; + struct snp_derived_key_req req; + int rc, resp_len; + + if (!arg->req_data || !arg->resp_data) + return -EINVAL; + + /* Copy the request payload from the userspace */ + if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req))) + return -EFAULT; + + /* Message version must be non-zero */ + if (!req.msg_version) + return -EINVAL; + + /* + * The intermediate response buffer is used while decrypting the + * response payload. Make sure that it has enough space to cover the + * authtag. + */ + resp_len = sizeof(resp->data) + crypto->a_len; + resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT); + if (!resp) + return -ENOMEM; + + /* Issue the command to get the attestation report */ + rc = handle_guest_request(snp_dev, req.msg_version, SNP_MSG_KEY_REQ, + &req.data, sizeof(req.data), resp->data, resp_len, + &arg->fw_err); + if (rc) + goto e_free; + + /* Copy the response payload to userspace */ + if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp))) + rc = -EFAULT; + +e_free: + kfree(resp); + return rc; +} + static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg) { struct snp_guest_dev *snp_dev = to_snp_dev(file); @@ -321,6 +365,10 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long ret = get_report(snp_dev, &input); break; } + case SNP_GET_DERIVED_KEY: { + ret = get_derived_key(snp_dev, &input); + break; + } default: break; } diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h index e8cfd15133f3..621a9167df7a 100644 --- a/include/uapi/linux/sev-guest.h +++ b/include/uapi/linux/sev-guest.h @@ -36,9 +36,33 @@ struct snp_user_guest_request { __u64 fw_err; }; +struct __snp_derived_key_req { + __u32 root_key_select; + __u32 rsvd; + __u64 guest_field_select; + __u32 vmpl; + __u32 guest_svn; + __u64 tcb_version; +}; + +struct snp_derived_key_req { + /* message version number (must be non-zero) */ + __u8 msg_version; + + struct __snp_derived_key_req data; +}; + +struct snp_derived_key_resp { + /* response data, see SEV-SNP spec for the format */ + __u8 data[64]; +}; + #define SNP_GUEST_REQ_IOC_TYPE 'S' /* Get SNP attestation report */ #define SNP_GET_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x0, struct snp_user_guest_request) +/* Get a derived key from the root */ +#define SNP_GET_DERIVED_KEY _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x1, struct snp_user_guest_request) + #endif /* __UAPI_LINUX_SEV_GUEST_H_ */ -- 2.17.1