linux-kernel - Re: [PATCH v2 2/2] efi/libstub: Add get_event

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Date: Mon, 19 Feb 2024 09:03:59 +0200
From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v2 2/2] efi/libstub: Add get_event_log() support for CC platforms

On Thu, 15 Feb 2024 at 05:02, Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>
> To allow event log info access after boot, EFI boot stub extracts
> the event log information and installs it in an EFI configuration
> table. Currently, EFI boot stub only supports installation of event
> log only for TPM 1.2 and TPM 2.0 protocols. Extend the same support
> for CC protocol. Since CC platform also uses TCG2 format, reuse TPM2
> support code as much as possible.
>
> Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#efi-cc-measurement-protocol [1]
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

[...]

> +void efi_retrieve_eventlog(void)
> +{
> +       efi_physical_addr_t log_location = 0, log_last_entry = 0;
> +       efi_guid_t cc_guid = EFI_CC_MEASUREMENT_PROTOCOL_GUID;
> +       efi_guid_t tpm2_guid = EFI_TCG2_PROTOCOL_GUID;
> +       int version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_2;
> +       efi_tcg2_protocol_t *tpm2 = NULL;
> +       efi_cc_protocol_t *cc = NULL;
> +       efi_bool_t truncated;
> +       efi_status_t status;
> +
> +       status = efi_bs_call(locate_protocol, &tpm2_guid, NULL, (void **)&tpm2);
> +       if (status == EFI_SUCCESS) {
> +               status = efi_call_proto(tpm2, get_event_log, version, &log_location,
> +                                       &log_last_entry, &truncated);
> +
> +               if (status != EFI_SUCCESS || !log_location) {
> +                       version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
> +                       status = efi_call_proto(tpm2, get_event_log, version,
> +                                               &log_location, &log_last_entry,
> +                                               &truncated);
> +                       if (status != EFI_SUCCESS || !log_location)
> +                               return;
> +               }
> +
> +               efi_retrieve_tcg2_eventlog(version, log_location, log_last_entry,
> +                                          truncated);
> +               return;
> +       }
> +
> +       status = efi_bs_call(locate_protocol, &cc_guid, NULL, (void **)&cc);
> +       if (status == EFI_SUCCESS) {
> +               version = EFI_CC_EVENT_LOG_FORMAT_TCG_2;
> +               status = efi_call_proto(cc, get_event_log, version, &log_location,
> +                                       &log_last_entry, &truncated);
> +               if (status != EFI_SUCCESS || !log_location)
> +                       return;
> +
> +               efi_retrieve_tcg2_eventlog(version, log_location, log_last_entry,
> +                                          truncated);
> +               return;
> +       }
> +}

[...]

I haven't looked into CC measurements much, but do we always want to
prioritize the tcg2 protocol? IOW if you have firmware that implements
both, shouldn't we prefer the CC protocol for VMs?

Thanks
/Ilias