On 2/4/24 2:03 PM, Ard Biesheuvel wrote: > On Sun, 4 Feb 2024 at 21:28, Kuppuswamy Sathyanarayanan > <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote: >> +Jiewen & Ken (RTMR firmware owner) >> >> On 2/3/24 10:46 PM, James Bottomley wrote: >>> On Sat, 2024-02-03 at 07:57 +0000, Kuppuswamy Sathyanarayanan wrote: >>>> If the virtual firmware implements TPM support, TCG2 protocol will be >>>> used for kernel measurements and event logging support. But in CC >>>> environment, not all platforms support or enable the TPM feature. >>>> UEFI specification [1] exposes protocol and interfaces used for >>>> kernel measurements in CC platforms without TPM support. >>>> >>>> Currently, the efi-stub only supports the kernel related measurements >>>> for the platform that supports TCG2 protocol. So, extend it add >>>> CC measurement protocol (EFI_CC_MEASUREMENT_PROTOCOL) and event >>>> logging support. Event logging format in the CC environment is the >>>> same as TCG2. >>> Why do we have to do this anymore? Given that you're already pushing >>> patches that map RTMRs to TPM PCRs: >>> >>> https://lore.kernel.org/lkml/20240128212532.2754325-4-sameo@xxxxxxxxxxxx/ >> IMHO, I am not sure whether we need this mapping support . I have already >> mentioned the same comment in [1]. If we support extension and logging >> via configFS ABI, why again support PCR mapping? >> >> https://lore.kernel.org/lkml/2bd7c80b-9cd8-4450-a410-c3739d224167@xxxxxxxxxxxxxxx/ [1] >> >>> Can't you just add a stub TCG2 driver to EFI that exposes only the >>> ability to log and measure using this mapping? That way all our >>> existing code will "just work" without the need to understand anything >>> about confidential computing or add new code to do the measurement? >> I am not familiar with the EFI implementation, but I think a new protocol >> is added to handle future CC extensions (which could deviate from >> TCG2) and to support platforms that does not support or enable TPM >> feature. So modifying the TCG2 driver in EFI may not work for the >> above-mentioned cases. I think the EFI driver part of this support >> is already merged. >> >> Jiewen/Ken may have more comments about this proposal. >> > I don't think it is sufficient to wire up the CC protocol here. There > is more code in drivers/firmware/efi/libstub/tpm.c that deals with the > event log. > > Given that the EFI CC protocol was specifically designed to act as a > substitute for the TCG2 protocol, I would expect all occurrences of > TCG2 protocol invocations to be handled accordingly. > > So I think the approach here should be to provide a local wrapper > around get_event_log() and hash_log_extend_event() that is backed by > either the TCG2 protocol of the EFI cc protocol, and all current > callers invoke this wrapper rather than the TCG2 protocol directly. Ah, I missed that part. Thanks for pointing out. I will fix this in next version. -- Sathyanarayanan Kuppuswamy Linux Kernel Developer
