Re: [PATCH RFC 0/3] security: ima: support TSM measurement registers

[Yeoreum Yun <yeoreum.yun@arm.com>]

Hi Roberto,

> On Thu, 2026-10-01 at 13:27 +0200, Roberto Sassu wrote:
> > On Wed, 2026-09-30 at 14:43 +0100, Yeoreum Yun wrote:
> > > Confidential computing guests without a TPM can use TSM measurement
> > > registers to record IMA measurement digests instead of TPM PCRs.
> 
> + Gong Ruiqi, of course.
> 
> Roberto
> 
> > Hi Yeoreum
> > 
> > a similar patch set has been sent to the linux-integrity mailing list:
> > 
> > https://lore.kernel.org/linux-integrity/20250630125928.765285-1-gongruiqi1@huawei.com/
> > 
> > Could you please work with Gong Ruiqi to have a unified proposal?
> > 
> > Thanks
> > 
> > Roberto
> > 

Thanks for letting me know and I think the proposal is almost the same
with the different terminology only.

@Gong, what do you think?

> > > This series introduces in-kernel interfaces for accessing TSM
> > > measurement registers, abstracts IMA's measurement-register operations,
> > > and adds a TSM backend for Intel TDX and Arm CCA.
> > > 
> > > The following mappings between TPM PCR indices and TSM measurement
> > > registers are defined for Intel TDX [0] and proposed for Arm CCA [1]:
> > > 
> > >   TPM PCR index | Intel TDX register | Arm CCA register
> > >   --------------+--------------------+-----------------
> > >   0             | MRTD               | RIM
> > >   1, 7          | RTMR[0]            | REM[0]
> > >   2-6           | RTMR[1]            | REM[1]
> > >   8-15          | RTMR[2]            | REM[2]
> > > 
> > > These mappings allow IMA to translate PCR indices into the corresponding
> > > TSM measurement registers.
> > > 
> > > The TPM backend remains preferred when it is available at IMA
> > > initialization. Otherwise, IMA falls back to a supported TSM backend.
> > > Only one backend is selected; IMA measurements are not extended to both
> > > TPM PCRs and TSM measurement registers.
> > > 
> > > The attestation proccess for guest with TSM measurement register will
> > > be done with Confidential Compute Event Log (CCEL) which is exported by
> > > /sys/firmware/acpi/tables/data/CCEL. Here is brief process in arm64:
> > > 
> > >   Verifier                 Realm guest              RMM / Platform
> > >      |                         |                           |
> > >      |--- Challenge (nonce) -->|                           |
> > >      |                         |--- Request token -------->|
> > >      |                         |    with challenge         |
> > >      |                         |                           |
> > >      |                         |<-- CCA token T -----------|
> > >      |<-- CCA token T ---------|                           |
> > >      |<-- CCEL event log ------|                           |
> > >      |<-- IMA measurement log -|                           |
> > >      |                         |                           |
> > >  Verify token T:               |                           |
> > >   - signatures                 |                           |
> > >   - Platform/Realm             |                           |
> > >     token binding              |                           |
> > >   - challenge freshness        |                           |
> > >   - platform/RIM policy        |                           |
> > >   - verify measurement logs    |                           |
> > >      |                         |                           |
> > >      | ----ACCEPT / REJECT---->|                           |
> > > 
> > > This patch based on arm-cca-mr series [3].
> > > 
> > > Link: [0] https://uefi.org/specs/UEFI/2.11/38_Confidential_Computing.html#intel-trust-domain-extension
> > > Link: [1] https://github.com/tianocore/edk2/issues/11383
> > > Link: [2] https://github.com/tianocore/edk2/issues/11384
> > > Link: [3] https://lore.kernel.org/all/20260929-arm_cca_mr-v2-0-1d98bba187fd@arm.com/
> > > 
> > > ---
> > > Yeoreum Yun (3):
> > >       virt: coco: introduce tsm_default_tm() and tsm_mr_read()/write()
> > >       security: IMA: introduce ima_mr structure
> > >       security: IMA: use TSM measurement registers
> > > 
> > >  drivers/virt/coco/guest/tsm-mr.c          | 159 +++++++++++++---
> > >  include/linux/tsm-mr.h                    |  26 +++
> > >  security/integrity/ima/Makefile           |   3 +-
> > >  security/integrity/ima/ima.h              |   7 +-
> > >  security/integrity/ima/ima_api.c          |   4 +-
> > >  security/integrity/ima/ima_crypto.c       | 137 +++++---------
> > >  security/integrity/ima/ima_fs.c           |  16 +-
> > >  security/integrity/ima/ima_init.c         |   7 +-
> > >  security/integrity/ima/ima_mr.c           |  48 +++++
> > >  security/integrity/ima/ima_mr.h           |  76 ++++++++
> > >  security/integrity/ima/ima_mr_tpm.c       | 155 ++++++++++++++++
> > >  security/integrity/ima/ima_mr_tsm.c       | 290 ++++++++++++++++++++++++++++++
> > >  security/integrity/ima/ima_queue.c        |  39 ++--
> > >  security/integrity/ima/ima_template.c     |   4 +-
> > >  security/integrity/ima/ima_template_lib.c |   2 +-
> > >  15 files changed, 819 insertions(+), 154 deletions(-)
> > > ---
> > > base-commit: b561246f45174b7472c24b75358ea95bae72b7b8
> > > change-id: 20260929-ima_tgx_integration_v2-1c54aeeaeaee
> > > 
> > > Best regards,
> 

-- 
Sincerely,
Yeoreum Yun