Re: [PATCH v7 0/5] Allow guest access to EFI confidential computing secret area

Greg KH
2022-02-01T13:50:58Z

On Tue, Feb 01, 2022 at 12:44:08PM +0000, Dov Murik wrote:
> 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 keeps the address of the EFI-provided memory for
> injected secrets, and exposes the secrets to userspace via securityfs
> using a new efi_secret kernel module. The module is autoloaded (by the
> EFI driver) if the secret area is populated.
>
> The first patch in EFI keeps the address of the secret area as passed in
> the EFI configuration table. The second patch is a quirk fix for older
> firmwares didn't mark the secrets page as EFI_RESERVED_TYPE. 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. The fourth patch auto-loads the
> efi_secret module during startup if the injected secrets area is
> populated. The last patch documents the data flow of confidential
> computing secret injection.
>
> 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.
>
> To enable this functionality, set CONFIG_EFI_SECRET=m when building the
> guest kernel.
>
> 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:
>
> # 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

Please see my comments on the powerpc version of this type of thing:
https://lore.kernel.org/r/20220122005637.28199-1-nayna@linux.ibm.com

You all need to work together to come up with a unified place for this
and stop making it platform-specific.

Until then, we can't take this.

sorry,

greg k-h