| Message ID | 20250228170720.144739-1-sgarzare@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Enlightened vTPM support for SVSM on SEV-SNP | expand |
On Fri, Feb 28, 2025 at 06:07:14PM +0100, Stefano Garzarella wrote: > I put RFC back in because we haven't yet decided if this is the best > approach to support SVSM vTPM, but I really like to receive feedbacks > especially from the maintainer/reviewers of the TPM subsystem, to see if > this approach is acceptable. I didn't look in high detail, but the overall shape is what I was thinking about in our previous conversations. Very little TPM code is under arch/, we have a nice simplifying helper in the core code, and you have a tidy platform device to tie it all together. Jason
On Fri, Feb 28, 2025 at 08:30:09PM -0400, Jason Gunthorpe wrote: >On Fri, Feb 28, 2025 at 06:07:14PM +0100, Stefano Garzarella wrote: >> I put RFC back in because we haven't yet decided if this is the best >> approach to support SVSM vTPM, but I really like to receive feedbacks >> especially from the maintainer/reviewers of the TPM subsystem, to see if >> this approach is acceptable. > >I didn't look in high detail, but the overall shape is what I was >thinking about in our previous conversations. Very little TPM code is >under arch/, we have a nice simplifying helper in the core code, and >you have a tidy platform device to tie it all together. Thank you so much for taking a look and confirming that I understood your suggestions correctly! Stefano
I put RFC back in because we haven't yet decided if this is the best approach to support SVSM vTPM, but I really like to receive feedbacks especially from the maintainer/reviewers of the TPM subsystem, to see if this approach is acceptable. Also James, Claudio, I left some questions for you in patches 2 and 4, since I reused your code, but I changed the context quite a bit, so for now I reset the author and added C-o-b, but I'm not sure it's okay for you. As requested, I try to add more context: 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 [3]. 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 [1]. In the meantime, the patches have been maintained and tested in the Coconut Linux fork [2] along with the work to support the vTPM emulation in Coconut SVSM. The first two patches add public APIs to use AMD SVSM vTPM. They use SVSM_VTPM_QUERY call to probe for the vTPM device and SVSM_VTPM_CMD call to execute vTPM operations as defined in the AMD SVSM spec [3]. The third patch add a new send_recv() tpm_class_ops callback as suggested by Jason to be used with devices that do not support interrupts and provide a single operation to send the command and receive the response on the same buffer. The fourth patch adds an interface to talk to emulated devices via the TCG reference implementation and then used by the fifth patch to implement the SVSM vTPM driver. The sixth patch simply registers the platform device. Since all SEV-SNP dependencies are now upstream, this series can be applied directly to the Linus' tree. These patches were tested in an AMD SEV-SNP guest running: - a recent version of Coconut SVSM [4] containing an ephemeral vTPM - a PoC [5] containing a stateful vTPM used for sealing/unsealing a LUKS key Changelog: v1 -> v2 RFC - Added send_recv() tpm_class_ops callback - Removed the intermediate tpm_platform.ko driver - Renamed tpm_platform.h to tpm_tcgsim.h and included some API to fill TPM_SEND_COMMAND requests and parse responses from a device emulated using the TCG Simulatore reference implementation - Added public API in x86/sev usable to discover and talk with the SVSM vTPM - Added the tpm-svsm platform driver in driver/char/tpm/ - Fixed some SVSM TPM related issues (resp_size as u32, don't fail on features !=0, s/VTPM/vTPM) v0 RFC -> v1: https://lore.kernel.org/linux-integrity/20241210143423.101774-1-sgarzare@redhat.com/ - Used SVSM_VTPM_QUERY to probe the TPM as Tom Lendacky suggested - Changed references/links to TCG TPM repo since in the last year MS donated the reference TPM implementation to the TCG. - Addressed Dov Murik's comments: https://lore.kernel.org/all/f7d0bd07-ba1b-894e-5e39-15fb1817bc8b@linux.ibm.com/ - Added a new patch with SVSM call macros for the vTPM protocol, following what we already have for SVSM_CORE and SVSM_ATTEST - Rebased on v6.13-rc2 Thanks, Stefano [1] https://lore.kernel.org/all/acb06bc7f329dfee21afa1b2ff080fe29b799021.camel@linux.ibm.com/ [2] https://github.com/coconut-svsm/linux/tree/svsm [3] "Secure VM Service Module for SEV-SNP Guests" Publication # 58019 Revision: 1.00 https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf [4] https://github.com/coconut-svsm/svsm/commit/6522c67e1e414f192a6f014b122ca8a1066e3bf5 [5] https://github.com/stefano-garzarella/snp-svsm-vtpm Stefano Garzarella (6): x86/sev: add SVSM call macros for the vTPM protocol x86/sev: add SVSM vTPM probe/send_command functions tpm: add send_recv() ops in tpm_class_ops tpm: add interface to interact with devices based on TCG Simulator tpm: add SNP SVSM vTPM driver x86/sev: register tpm-svsm platform device arch/x86/include/asm/sev.h | 7 ++ include/linux/tpm.h | 2 + include/linux/tpm_tcgsim.h | 136 +++++++++++++++++++++++++++++++ arch/x86/coco/sev/core.c | 55 +++++++++++++ drivers/char/tpm/tpm-interface.c | 8 +- drivers/char/tpm/tpm_svsm.c | 120 +++++++++++++++++++++++++++ drivers/char/tpm/Kconfig | 10 +++ drivers/char/tpm/Makefile | 1 + 8 files changed, 338 insertions(+), 1 deletion(-) create mode 100644 include/linux/tpm_tcgsim.h create mode 100644 drivers/char/tpm/tpm_svsm.c base-commit: ac9c34d1e45a4c25174ced4fc0cfc33ff3ed08c7 prerequisite-patch-id: 46b3bb004bd044863a404b15d704b0ab5cb3adf3 prerequisite-patch-id: 6448736bc6cd561e6ddc10d21f43952a585c5657 prerequisite-patch-id: 9dd308a4f5a115129c6c1b403083651ade63a3de prerequisite-patch-id: 0a97c8378dbe85c3547a39ecb008190b84c7e797 prerequisite-patch-id: 776de0155dee63ac4ad062e30c97ba09c2d3da83 prerequisite-patch-id: 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