Re: [PATCH v2 1/2] efi/libstub: Add Confidential Computing (CC) measurement support

[Ilias Apalodimas]

Hi Kuppuswamy,

On Thu, 15 Feb 2024 at 05:02, Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> 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.
>
> More details about the EFI CC measurements and logging can be found
> in [1].
>
> Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#efi-cc-measurement-protocol [1]
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> ---
>
> Changes since v1:
> * Fixed missing tagged event data.
>
>  .../firmware/efi/libstub/efi-stub-helper.c    | 127 ++++++++++++++----
>  drivers/firmware/efi/libstub/efistub.h        |  74 ++++++++++
>  include/linux/efi.h                           |   1 +
>  3 files changed, 174 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> index bfa30625f5d0..cc31f8143190 100644
> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> @@ -219,50 +219,121 @@ static const struct {
>         },
>  };
>
> +static efi_status_t tcg2_efi_measure(efi_tcg2_protocol_t *tcg2,
> +                                    unsigned long load_addr,
> +                                    unsigned long load_size,
> +                                    enum efistub_event event)
> +{
> +       struct efi_measured_event {
> +               efi_tcg2_event_t        event_data;
> +               efi_tcg2_tagged_event_t tagged_event;
> +               u8                      tagged_event_data[];
> +       } *evt;
> +       int size = sizeof(*evt) + events[event].event_data_len;

This is defined as size_t on the cc variant. I guess both are ok, just pick one

> +       efi_status_t status;
> +
> +       status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, size,
> +                            (void **)&evt);
> +       if (status != EFI_SUCCESS)

pr_err() here as done in the cc variant?

> +               return status;
> +
> +       evt->event_data = (struct efi_tcg2_event){
> +               .event_size                     = size,
> +               .event_header.header_size       = sizeof(evt->event_data.event_header),
> +               .event_header.header_version    = EFI_TCG2_EVENT_HEADER_VERSION,
> +               .event_header.pcr_index         = events[event].pcr_index,
> +               .event_header.event_type        = EV_EVENT_TAG,
> +       };
> +
> +       evt->tagged_event = (struct efi_tcg2_tagged_event){
> +               .tagged_event_id                = events[event].event_id,
> +               .tagged_event_data_size         = events[event].event_data_len,
> +       };
> +
> +       memcpy(evt->tagged_event_data, events[event].event_data,
> +              events[event].event_data_len);
> +
> +       status = efi_call_proto(tcg2, hash_log_extend_event, 0,
> +                               load_addr, load_size, &evt->event_data);

The struct filling/memcpying looks similar across the 2 functions.  I
wonder if it makes sense to have a common function for that, with an
argument for the event data type.

> +       efi_bs_call(free_pool, evt);
> +
> +       return status;
> +}
> +
> +static efi_status_t cc_efi_measure(efi_cc_protocol_t *cc,
> +                                  unsigned long load_addr,
> +                                  unsigned long load_size,
> +                                  enum efistub_event event)
> +{
> +       struct efi_measured_event {
> +               efi_cc_event_t  event_data;
> +               efi_tcg2_tagged_event_t tagged_event;
> +               u8                      tagged_event_data[];
> +       } *evt;
> +       size_t size = sizeof(*evt) + events[event].event_data_len;
> +       efi_cc_mr_index_t mr;
> +       efi_status_t status;
> +
> +       status = efi_call_proto(cc, map_pcr_to_mr_index, events[event].pcr_index, &mr);
> +       if (status != EFI_SUCCESS) {
> +               efi_err("CC_MEASURE: PCR to MR mapping failed\n");
> +               return status;
> +       }
> +
> +       status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, size, (void **)&evt);
> +       if (status != EFI_SUCCESS) {
> +               efi_err("CC_MEASURE: Allocating event struct failed\n");
> +               return status;
> +       }
> +
> +       evt->event_data = (struct efi_cc_event){
> +               .event_size                     = size,
> +               .event_header.header_size       = sizeof(evt->event_data.event_header),
> +               .event_header.header_version    = EFI_CC_EVENT_HEADER_VERSION,
> +               .event_header.mr_index          = mr,
> +               .event_header.event_type        = EV_EVENT_TAG,
> +       };
> +
> +       evt->tagged_event = (struct efi_tcg2_tagged_event){
> +               .tagged_event_id                = events[event].event_id,
> +               .tagged_event_data_size         = events[event].event_data_len,
> +       };
> +
> +       memcpy(evt->tagged_event_data, events[event].event_data,
> +              events[event].event_data_len);
> +
> +       status = efi_call_proto(cc, hash_log_extend_event, 0,
> +                               load_addr, load_size, &evt->event_data);
> +
> +       efi_bs_call(free_pool, evt);
> +
> +       return status;
> +}
>  static efi_status_t efi_measure_tagged_event(unsigned long load_addr,
>                                              unsigned long load_size,
>                                              enum efistub_event event)
>  {
>         efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
> +       efi_guid_t cc_guid = EFI_CC_MEASUREMENT_PROTOCOL_GUID;
> +       efi_cc_protocol_t *cc = NULL;
>         efi_tcg2_protocol_t *tcg2 = NULL;
>         efi_status_t status;
>
>         efi_bs_call(locate_protocol, &tcg2_guid, NULL, (void **)&tcg2);
>         if (tcg2) {
> -               struct efi_measured_event {
> -                       efi_tcg2_event_t        event_data;
> -                       efi_tcg2_tagged_event_t tagged_event;
> -                       u8                      tagged_event_data[];
> -               } *evt;
> -               int size = sizeof(*evt) + events[event].event_data_len;
> -
> -               status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, size,
> -                                    (void **)&evt);
> +               status = tcg2_efi_measure(tcg2, load_addr, load_size, event);
>                 if (status != EFI_SUCCESS)
>                         goto fail;
>
> -               evt->event_data = (struct efi_tcg2_event){
> -                       .event_size                     = size,
> -                       .event_header.header_size       = sizeof(evt->event_data.event_header),
> -                       .event_header.header_version    = EFI_TCG2_EVENT_HEADER_VERSION,
> -                       .event_header.pcr_index         = events[event].pcr_index,
> -                       .event_header.event_type        = EV_EVENT_TAG,
> -               };
> -
> -               evt->tagged_event = (struct efi_tcg2_tagged_event){
> -                       .tagged_event_id                = events[event].event_id,
> -                       .tagged_event_data_size         = events[event].event_data_len,
> -               };
> -
> -               memcpy(evt->tagged_event_data, events[event].event_data,
> -                      events[event].event_data_len);
> -
> -               status = efi_call_proto(tcg2, hash_log_extend_event, 0,
> -                                       load_addr, load_size, &evt->event_data);
> -               efi_bs_call(free_pool, evt);
> +               return EFI_SUCCESS;
> +       }
>
> +       efi_bs_call(locate_protocol, &cc_guid, NULL, (void **)&cc);
> +       if (cc) {
> +               status = cc_efi_measure(cc, load_addr, load_size, event);
>                 if (status != EFI_SUCCESS)
>                         goto fail;
> +
>                 return EFI_SUCCESS;
>         }
>

[...]

Thanks
/Ilias