Re: [PATCH V7 4/4] efi: Attempt to get the TCG2 event log in the boot stub

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Mon, 20 May 2019 at 21:55, Matthew Garrett <matthewgarrett@google.com> wrote:
>
> From: Matthew Garrett <mjg59@google.com>
>
> Right now we only attempt to obtain the SHA1-only event log. The
> protocol also supports a crypto agile log format, which contains digests
> for all algorithms in use. Attempt to obtain this first, and fall back
> to obtaining the older format if the system doesn't support it. This is
> lightly complicated by the event sizes being variable (as we don't know
> in advance which algorithms are in use), and the interface giving us
> back a pointer to the start of the final entry rather than a pointer to
> the end of the log - as a result, we need to parse the final entry to
> figure out its length in order to know how much data to copy up to the
> OS.
>
> Signed-off-by: Matthew Garrett <mjg59@google.com>

Provided that this gets a tested-by from Bartosz,

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

> ---
>  drivers/firmware/efi/libstub/tpm.c | 50 ++++++++++++++++++++----------
>  1 file changed, 33 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/efi/libstub/tpm.c
> index 5bd04f75d8d6..6b3b507a54eb 100644
> --- a/drivers/firmware/efi/libstub/tpm.c
> +++ b/drivers/firmware/efi/libstub/tpm.c
> @@ -57,7 +57,7 @@ void efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg)
>
>  #endif
>
> -static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
> +void efi_retrieve_tpm2_eventlog(efi_system_table_t *sys_table_arg)
>  {
>         efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
>         efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
> @@ -67,6 +67,7 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
>         unsigned long first_entry_addr, last_entry_addr;
>         size_t log_size, last_entry_size;
>         efi_bool_t truncated;
> +       int version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_2;
>         void *tcg2_protocol = NULL;
>
>         status = efi_call_early(locate_protocol, &tcg2_guid, NULL,
> @@ -74,14 +75,20 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
>         if (status != EFI_SUCCESS)
>                 return;
>
> -       status = efi_call_proto(efi_tcg2_protocol, get_event_log, tcg2_protocol,
> -                               EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2,
> -                               &log_location, &log_last_entry, &truncated);
> -       if (status != EFI_SUCCESS)
> -               return;
> +       status = efi_call_proto(efi_tcg2_protocol, get_event_log,
> +                               tcg2_protocol, 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(efi_tcg2_protocol, get_event_log,
> +                                       tcg2_protocol, version, &log_location,
> +                                       &log_last_entry, &truncated);
> +               if (status != EFI_SUCCESS || !log_location)
> +                       return;
> +
> +       }
>
> -       if (!log_location)
> -               return;
>         first_entry_addr = (unsigned long) log_location;
>
>         /*
> @@ -96,8 +103,23 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
>                  * We need to calculate its size to deduce the full size of
>                  * the logs.
>                  */
> -               last_entry_size = sizeof(struct tcpa_event) +
> -                       ((struct tcpa_event *) last_entry_addr)->event_size;
> +               if (version == EFI_TCG2_EVENT_LOG_FORMAT_TCG_2) {
> +                       /*
> +                        * The TCG2 log format has variable length entries,
> +                        * and the information to decode the hash algorithms
> +                        * back into a size is contained in the first entry -
> +                        * pass a pointer to the final entry (to calculate its
> +                        * size) and the first entry (so we know how long each
> +                        * digest is)
> +                        */
> +                       last_entry_size =
> +                               __calc_tpm2_event_size((void *)last_entry_addr,
> +                                                   (void *)(long)log_location,
> +                                                   false);
> +               } else {
> +                       last_entry_size = sizeof(struct tcpa_event) +
> +                          ((struct tcpa_event *) last_entry_addr)->event_size;
> +               }
>                 log_size = log_last_entry - log_location + last_entry_size;
>         }
>
> @@ -114,7 +136,7 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
>
>         memset(log_tbl, 0, sizeof(*log_tbl) + log_size);
>         log_tbl->size = log_size;
> -       log_tbl->version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
> +       log_tbl->version = version;
>         memcpy(log_tbl->log, (void *) first_entry_addr, log_size);
>
>         status = efi_call_early(install_configuration_table,
> @@ -126,9 +148,3 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
>  err_free:
>         efi_call_early(free_pool, log_tbl);
>  }
> -
> -void efi_retrieve_tpm2_eventlog(efi_system_table_t *sys_table_arg)
> -{
> -       /* Only try to retrieve the logs in 1.2 format. */
> -       efi_retrieve_tpm2_eventlog_1_2(sys_table_arg);
> -}
> --
> 2.21.0.1020.gf2820cf01a-goog
>