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

[Dr. David Alan Gilbert]

* Brijesh Singh (brijesh.singh@xxxxxxx) wrote:
> Hi Dov,
> 
> 
> On 5/13/21 1:26 AM, Dov Murik wrote:
> > 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.
> >
> > 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 May 12 18:03 .
> > drwxr-xr-x 3 root root 0 May 12 18:02 ..
> > -r--r----- 1 root root 0 May 12 18:03 736870e5-84f0-4973-92ec-06879ce3da0b
> > -r--r----- 1 root root 0 May 12 18:03 83c83f7f-1356-4975-8b7e-d3a0b54312c6
> > -r--r----- 1 root root 0 May 12 18:03 9553f55d-3da2-43ee-ab5d-ff17f78864d2
> > -r--r----- 1 root root 0 May 12 18:03 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                                     ..
> 
> I am adding a new virt driver to help get the attestation report for the
> SEV-SNP guest. I understand they both are different, in case of the SEV
> the attestation is already completed and we are simply exposing the
> secret provided after the attestation to the userspace, whereas in SNP,
> the userspace is querying the attestation and will probably derive keys
> etc based on the attestation report. I am wondering if we should merge
> both the SEV secret and SNP attestation query in a single driver ?
> Should we cover usecases where SEV guest is not booted under the EFI ?
> Also, it appears that this driver need to be manually loaded, should we
> create a platform device so that the driver binds to platform device and
> use the resource structure to find the location of the secret data?

The nice thing about Dov's device/file is that it's a simple text file
that userspace can then read the secret out of;  I'm not sure if there's
anything similar in SNP (or for that matter TDX, cc'ing in Andi)

Dave

> I was trying to answer some of these questions SNP series. See these patches
> 
> https://marc.info/?l=kvm&m=161978514019741&w=2
> 
> https://marc.info/?l=kvm&m=161978514119744&w=2
> 
> https://marc.info/?l=kvm&m=161978514219751&w=2
> 
> 
> >
> > [1] https://github.com/tianocore/edk2/commit/01726b6d23d4
> >
> >
> > Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
> > Cc: Ashish Kalra <ashish.kalra@xxxxxxx>
> > Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > Cc: James Bottomley <jejb@xxxxxxxxxxxxx>
> > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > Cc: James Morris <jmorris@xxxxxxxxx>
> > Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
> > Cc: linux-efi@xxxxxxxxxxxxxxx
> > Cc: linux-security-module@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> >
> > 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          | 260 ++++++++++++++++++
> >  include/linux/efi.h                           |  11 +
> >  14 files changed, 410 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: c06a2ba62fc401b7aaefd23f5d0bc06d2457ccc1
-- 
Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK