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Message-ID: <YKZAUdbikp2Pt0XV@work-vm>
Date: Thu, 20 May 2021 11:56:17 +0100
From: "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To: Brijesh Singh <brijesh.singh@....com>
Cc: Dov Murik <dovmurik@...ux.ibm.com>, linux-efi@...r.kernel.org,
Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
Tobin Feldman-Fitzthum <tobin@....com>,
Jim Cadden <jcadden@....com>,
James Bottomley <jejb@...ux.ibm.com>,
Hubertus Franke <frankeh@...ibm.com>,
Mike Rapoport <rppt@...ux.ibm.com>,
Laszlo Ersek <lersek@...hat.com>,
Ashish Kalra <ashish.kalra@....com>,
Tom Lendacky <thomas.lendacky@....com>,
Ard Biesheuvel <ardb@...nel.org>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, ak@...ux.intel.com,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] Allow access to confidential computing secret
area
* Brijesh Singh (brijesh.singh@....com) 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@...hat.com>
> > Cc: Ashish Kalra <ashish.kalra@....com>
> > Cc: Brijesh Singh <brijesh.singh@....com>
> > Cc: Tom Lendacky <thomas.lendacky@....com>
> > Cc: James Bottomley <jejb@...ux.ibm.com>
> > Cc: Ard Biesheuvel <ardb@...nel.org>
> > Cc: James Morris <jmorris@...ei.org>
> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
> > Cc: linux-efi@...r.kernel.org
> > Cc: linux-security-module@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> >
> > 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@...hat.com / Manchester, UK
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