Re: [PATCH 2/2] efi+tpm: don't traverse an event log with no events

[Ard Biesheuvel]

On Mon, 26 Aug 2019 at 18:30, Peter Jones <pjones@xxxxxxxxxx> wrote:
>
> When there are no entries to put into the final event log, some machines
> will return the template they would have populated anyway.  In this case
> the nr_events field is 0, but the rest of the log is just garbage.
>
> This patch stops us from trying to iterate the table with
> __calc_tpm2_event_size() when the number of events in the table is 0.
>
> Signed-off-by: Peter Jones <pjones@xxxxxxxxxx>
> Tested-by: Lyude Paul <lyude@xxxxxxxxxx>
> ---
>  drivers/firmware/efi/tpm.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
> index 1d3f5ca3eaa..be51ed17c6e 100644
> --- a/drivers/firmware/efi/tpm.c
> +++ b/drivers/firmware/efi/tpm.c
> @@ -75,11 +75,15 @@ int __init efi_tpm_eventlog_init(void)
>                 goto out;
>         }
>
> -       tbl_size = tpm2_calc_event_log_size((void *)efi.tpm_final_log
> -                                           + sizeof(final_tbl->version)
> -                                           + sizeof(final_tbl->nr_events),
> -                                           final_tbl->nr_events,
> -                                           log_tbl->log);
> +       tbl_size = 0;
> +       if (final_tbl->nr_events != 0) {
> +               void *events = (void *)efi.tpm_final_log
> +                               + sizeof(final_tbl->version)
> +                               + sizeof(final_tbl->nr_events);

Please put a newline here

With that fixed,

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

> +               tbl_size = tpm2_calc_event_log_size(events,
> +                                                   final_tbl->nr_events,
> +                                                   log_tbl->log);
> +       }
>         memblock_reserve((unsigned long)final_tbl,
>                          tbl_size + sizeof(*final_tbl));
>         early_memunmap(final_tbl, sizeof(*final_tbl));
> --
> 2.23.0.rc2
>