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1What: security/secrets/coco2Date: February 20223Contact: Dov Murik <dovmurik@linux.ibm.com>4Description:5 Exposes confidential computing (coco) EFI secrets to6 userspace via securityfs.7 8 EFI can declare memory area used by confidential computing9 platforms (such as AMD SEV and SEV-ES) for secret injection by10 the Guest Owner during VM's launch. The secrets are encrypted11 by the Guest Owner and decrypted inside the trusted enclave,12 and therefore are not readable by the untrusted host.13 14 The efi_secret module exposes the secrets to userspace. Each15 secret appears as a file under <securityfs>/secrets/coco,16 where the filename is the GUID of the entry in the secrets17 table. This module is loaded automatically by the EFI driver18 if the EFI secret area is populated.19 20 Two operations are supported for the files: read and unlink.21 Reading the file returns the content of secret entry.22 Unlinking the file overwrites the secret data with zeroes and23 removes the entry from the filesystem. A secret cannot be read24 after it has been unlinked.25 26 For example, listing the available secrets::27 28 # modprobe efi_secret29 # ls -l /sys/kernel/security/secrets/coco30 -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b31 -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c632 -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d233 -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a991034 35 Reading the secret data by reading a file::36 37 # cat /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a991038 the-content-of-the-secret-data39 40 Wiping a secret by unlinking a file::41 42 # rm /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a991043 # ls -l /sys/kernel/security/secrets/coco44 -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b45 -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c646 -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d247 48 Note: The binary format of the secrets table injected by the49 Guest Owner is described in50 drivers/virt/coco/efi_secret/efi_secret.c under "Structure of51 the EFI secret area".52