52 lines
2.2 KiB
Plaintext
52 lines
2.2 KiB
Plaintext
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What: security/secrets/coco
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Date: February 2022
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Contact: Dov Murik <dovmurik@linux.ibm.com>
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Description:
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Exposes confidential computing (coco) EFI secrets to
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userspace via securityfs.
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EFI can declare memory area used by confidential computing
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platforms (such as AMD SEV and SEV-ES) for secret injection by
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the Guest Owner during VM's launch. The secrets are encrypted
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by the Guest Owner and decrypted inside the trusted enclave,
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and therefore are not readable by the untrusted host.
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The efi_secret module exposes the secrets to userspace. Each
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secret appears as a file under <securityfs>/secrets/coco,
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where the filename is the GUID of the entry in the secrets
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table. This module is loaded automatically by the EFI driver
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if the EFI secret area is populated.
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Two operations are supported for the files: read and unlink.
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Reading the file returns the content of secret entry.
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Unlinking the file overwrites the secret data with zeroes and
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removes the entry from the filesystem. A secret cannot be read
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after it has been unlinked.
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For example, listing the available secrets::
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# modprobe efi_secret
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# ls -l /sys/kernel/security/secrets/coco
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-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
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-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
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-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
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-r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
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Reading the secret data by reading a file::
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# cat /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
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the-content-of-the-secret-data
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Wiping a secret by unlinking a file::
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# rm /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910
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# ls -l /sys/kernel/security/secrets/coco
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-r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
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-r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
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-r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
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Note: The binary format of the secrets table injected by the
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Guest Owner is described in
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drivers/virt/coco/efi_secret/efi_secret.c under "Structure of
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the EFI secret area".
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