Confidential computing (coco) hardware such as AMD SEV (Secure Encrypted Virtualization) allows guest owners to inject secrets into the VMs memory without the host/hypervisor being able to read them. In SEV, secret injection is performed early in the VM launch process, before the guest starts running. OVMF already reserves designated area for secret injection (in its AmdSev package; see edk2 commit 01726b6d23d4 "OvmfPkg/AmdSev: Expose the Sev Secret area using a configuration table" [1]), but the secrets were not available in the guest kernel. The patch series copies the secrets from the EFI-provided memory to kernel reserved memory, and optionally exposes them to userspace via securityfs using a new efi_secret kernel module. The first patch in efi/libstub copies the secret area from the EFI memory to specially allocated memory; the second patch reserves that memory block; and the third patch introduces the new efi_secret module that exposes the content of the secret entries as securityfs files, and allows clearing out secrets with a file unlink interface. As a usage example, consider a guest performing computations on encrypted files. The Guest Owner provides the decryption key (= secret) using the secret injection mechanism. The guest application reads the secret from the efi_secret filesystem and proceeds to decrypt the files into memory and then performs the needed computations on the content. In this example, the host can't read the files from the disk image because they are encrypted. Host can't read the decryption key because it is passed using the secret injection mechanism (= secure channel). Host can't read the decrypted content from memory because it's a confidential (memory-encrypted) guest. This has been tested with AMD SEV and SEV-ES guests, but the kernel side of handling the secret area has no SEV-specific dependencies, and therefore might be usable (perhaps with minor changes) for any confidential computing hardware that can publish the secret area via the standard EFI config table entry. Here is a simple example for usage of the efi_secret module in a guest to which an EFI secret area with 4 secrets was injected during launch: # modprobe efi_secret # ls -la /sys/kernel/security/coco/efi_secret total 0 drwxr-xr-x 2 root root 0 Jun 28 11:54 . drwxr-xr-x 3 root root 0 Jun 28 11:54 .. -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6 -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2 -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910 # xxd /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910 00000000: 7468 6573 652d 6172 652d 7468 652d 6b61 these-are-the-ka 00000010: 7461 2d73 6563 7265 7473 0001 0203 0405 ta-secrets...... 00000020: 0607 .. # rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910 # ls -la /sys/kernel/security/coco/efi_secret total 0 drwxr-xr-x 2 root root 0 Jun 28 11:55 . drwxr-xr-x 3 root root 0 Jun 28 11:54 .. -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6 -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2 [1] https://github.com/tianocore/edk2/commit/01726b6d23d4 --- v3 changes: - Rename the module to efi_secret - Remove the exporting of clean_cache_range - Use clflush_cache_range in wipe_memory - Document function wipe_memory - Initialize efi.coco_secret to EFI_INVALID_TABLE_ADDR to correctly detect when there's no secret area published in the EFI configuration tables v2: https://lore.kernel.org/linux-coco/20211007061838.1381129-1-dovmurik@xxxxxxxxxxxxx v2 changes: - Export clean_cache_range() - When deleteing a secret, call clean_cache_range() after explicit_memzero - Add Documentation/ABI/testing/securityfs-coco-sev_secret v1: https://lore.kernel.org/linux-coco/20210809190157.279332-1-dovmurik@xxxxxxxxxxxxx/ RFC: https://lore.kernel.org/linux-coco/20210628183431.953934-1-dovmurik@xxxxxxxxxxxxx/ Dov Murik (3): efi/libstub: Copy confidential computing secret area efi: Reserve confidential computing secret area virt: Add efi_secret module to expose confidential computing secrets .../ABI/testing/securityfs-coco-efi_secret | 50 +++ arch/x86/platform/efi/efi.c | 1 + drivers/firmware/efi/Makefile | 2 +- drivers/firmware/efi/coco.c | 41 +++ drivers/firmware/efi/efi.c | 4 + drivers/firmware/efi/libstub/Makefile | 2 +- drivers/firmware/efi/libstub/coco.c | 68 ++++ drivers/firmware/efi/libstub/efi-stub.c | 2 + drivers/firmware/efi/libstub/efistub.h | 2 + drivers/firmware/efi/libstub/x86-stub.c | 2 + drivers/virt/Kconfig | 3 + drivers/virt/Makefile | 1 + drivers/virt/coco/efi_secret/Kconfig | 10 + drivers/virt/coco/efi_secret/Makefile | 2 + drivers/virt/coco/efi_secret/efi_secret.c | 324 ++++++++++++++++++ include/linux/efi.h | 9 + 16 files changed, 521 insertions(+), 2 deletions(-) create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret create mode 100644 drivers/firmware/efi/coco.c create mode 100644 drivers/firmware/efi/libstub/coco.c create mode 100644 drivers/virt/coco/efi_secret/Kconfig create mode 100644 drivers/virt/coco/efi_secret/Makefile create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c base-commit: 60a9483534ed0d99090a2ee1d4bb0b8179195f51 -- 2.25.1
