linux-kernel - Re: [PATCH v2 3/5] virt: sevguest: Prep for kernel internal {get, get_ext}

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Date:   Wed, 16 Aug 2023 12:38:38 -0700
From:   Dionna Amalie Glaze <dionnaglaze@...gle.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>, linux-coco@...ts.linux.dev,
        Borislav Petkov <bp@...en8.de>,
        Brijesh Singh <brijesh.singh@....com>, peterz@...radead.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] virt: sevguest: Prep for kernel internal {get, get_ext}_report()

> Definitely, instead it was this comment from James that gave me pause:
>
> "To get a bit off topic, I'm not sure derived keys are much use.  The
> problem is in SNP that by the time the PSP does the derivation, the key
> is both tied to the physical system and derived from a measurement too
> general to differentiate between VM images (so one VM could read
> another VMs stored secrets)."
>

Key derivation on AMD SEV-SNP is not necessarily tied to a physical
system with the introduction of VLEK-based attestation. It's now tied
to a CSP's fleet of machines. We can use key derivation in the SVSM as
a basis for further key derivation based on measurement registers, so
the utility increases to provide something like persisted sealed data
that can only be unsealed when the SVSM witnesses a particular runtime
measurement configuration.
We can use NIST 800-90A Rev. 1 for combining keys from the PSP with
measurement register values for example.

> http://lore.kernel.org/r/c6576d1682b576ba47556478a98f397ed518a177.camel@HansenPartnership.com

--
-Dionna Glaze, PhD (she/her)