The Linux 6.16 kernel this summer will likely see the new SNP SVSM vTPM driver introduced for further enhancing the AMD EPYC confidential computing capabilities atop the mainline Linux kernel.
Queued this week via the tip/tip.git x86/sev Git branch is this SNP SVSM vTPM driver for recent EPYC CPUs boasting Secure Encrypted Virtualization Secure Nested Paging (SEV-SNP) capabilities. With the driver making it now to a tip/tip.git branch, it will likely be submitted for the next merge window (Linux 6.16 in June) barring any new problems from arising with the code or other objections being raised.
Stefano Garzarella of Red Hat spearheaded the effort on this new Linux driver for helping the AMD virtualization confidential computing effort. Stefano explains of this new driver in the patch series now queued in the TIP branch:
“AMD SEV-SNP defined a new mechanism for adding privileged levels (VMPLs) in the context of a Confidential VM. These levels can be used to run the guest OS at a lower privilege level than a Secure VM Service Module (SVSM). In this way SVSM can be used to emulate those devices (such as TPM) that cannot be delegated to an untrusted host.
The guest OS can talk to SVSM using a specific calling convention and instructions (a kind of system call/hyper call) and request services such as TPM emulation.
The main goal of this series is to add a driver for the vTPM defined by the AMD SVSM spec. The specification defines a protocol that a
SEV-SNP guest OS (running on VMPL >= 1) can use to discover and talk to a vTPM emulated by the SVSM in the guest context, but at a more
privileged level (VMPL0).This series is based on the RFC sent by James last year. In the meantime, the patches have been maintained and tested in the Coconut Linux fork along with the work to support the vTPM emulation in Coconut SVSM.”
This new driver is gated by the TCG_SVSM Kconfig switch.
Nice to see more of the AMD SEV-SNP / Trusted Computing / Confidential Computing work nearing the mainline kernel. Like with Intel and their Trust Domain Extensions (TDX) enablement, some elements of the upstreaming have dragged on for quite some time and multiple rounds of code review.
