[RFC PATCH v2 0/3] Allow access to confidential computing secret area

[Dov Murik]

Confidential computing 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.

Support for secret injection is already available in OVMF (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 sev_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 sev_secret module
that exposes the content of the secret entries as securityfs files, and
allows clearing out secrets with a file unlink interface.

This has been tested with AMD SEV guests, but the kernel side of
handling the secret area has no SEV-specific dependencies, and therefore
should be usable 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 sev_secret module in a guest to which
secrets were injected during launch:

# modprobe sev_secret
# ls -la /sys/kernel/security/sev_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/sev_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/sev_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910

# ls -la /sys/kernel/security/sev_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

v2 changes:
 - Add unlink support in sev_secret securityfs.


Dov Murik (3):
  efi/libstub: Copy confidential computing secret area
  efi: Reserve confidential computing secret area
  virt: Add sev_secret module to expose confidential computing secrets

 drivers/firmware/efi/Makefile                 |   2 +-
 drivers/firmware/efi/confidential-computing.c |  41 +++
 drivers/firmware/efi/efi.c                    |   5 +
 drivers/firmware/efi/libstub/Makefile         |   3 +-
 .../efi/libstub/confidential-computing.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                          |   2 +
 drivers/virt/Makefile                         |   1 +
 drivers/virt/sev_secret/Kconfig               |  11 +
 drivers/virt/sev_secret/Makefile              |   2 +
 drivers/virt/sev_secret/sev_secret.c          | 298 ++++++++++++++++++
 include/linux/efi.h                           |  11 +
 14 files changed, 448 insertions(+), 2 deletions(-)
 create mode 100644 drivers/firmware/efi/confidential-computing.c
 create mode 100644 drivers/firmware/efi/libstub/confidential-computing.c
 create mode 100644 drivers/virt/sev_secret/Kconfig
 create mode 100644 drivers/virt/sev_secret/Makefile
 create mode 100644 drivers/virt/sev_secret/sev_secret.c


base-commit: 62fb9874f5da54fdb243003b386128037319b219
-- 
2.25.1