Re: [PATCH v3] tpm: only set efi_tpm_final_log_size after successful event log parsing

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

On Wed, 25 Sep 2019 at 19:27, Jerry Snitselaar <jsnitsel@redhat.com> wrote:
>
> If __calc_tpm2_event_size fails to parse an event it will return 0,
> resulting tpm2_calc_event_log_size returning -1. Currently there is
> no check of this return value, and efi_tpm_final_log_size can end up
> being set to this negative value resulting in a panic like the
> the one given below.
>
> Also __calc_tpm2_event_size returns a size of 0 when it fails
> to parse an event, so update function documentation to reflect this.
>
...
>
> The root cause of the issue that caused the failure of event parsing
> in this case is resolved by Peter Jone's patchset dealing with large
> event logs where crossing over a page boundary causes the page with
> the event count to be unmapped.
>
> Fixes: c46f3405692de ("tpm: Reserve the TPM final events table")
> Cc: linux-efi@vger.kernel.org
> Cc: linux-integrity@vger.kernel.org
> Cc: stable@vger.kernel.org
> Cc: Matthew Garrett <mjg59@google.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>

Thanks Jerry, I have queued this in the efi/urgent branch.


> ---
> v3: rebase on top of Peter Jone's patchset
> v2: added FW_BUG to pr_err, and renamed label to out_calc.
>     Updated doc comment for __calc_tpm2_event_size.
>
>  drivers/firmware/efi/tpm.c   | 9 ++++++++-
>  include/linux/tpm_eventlog.h | 2 +-
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
> index b9ae5c6f9b9c..703469c1ab8e 100644
> --- a/drivers/firmware/efi/tpm.c
> +++ b/drivers/firmware/efi/tpm.c
> @@ -85,11 +85,18 @@ int __init efi_tpm_eventlog_init(void)
>                                                     final_tbl->nr_events,
>                                                     log_tbl->log);
>         }
> +
> +       if (tbl_size < 0) {
> +               pr_err(FW_BUG "Failed to parse event in TPM Final Events Log\n");
> +               goto out_calc;
> +       }
> +
>         memblock_reserve((unsigned long)final_tbl,
>                          tbl_size + sizeof(*final_tbl));
> -       early_memunmap(final_tbl, sizeof(*final_tbl));
>         efi_tpm_final_log_size = tbl_size;
>
> +out_calc:
> +       early_memunmap(final_tbl, sizeof(*final_tbl));
>  out:
>         early_memunmap(log_tbl, sizeof(*log_tbl));
>         return ret;
> diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
> index 12584b69a3f3..2dfdd63ac034 100644
> --- a/include/linux/tpm_eventlog.h
> +++ b/include/linux/tpm_eventlog.h
> @@ -152,7 +152,7 @@ struct tcg_algorithm_info {
>   * total. Once we've done this we know the offset of the data length field,
>   * and can calculate the total size of the event.
>   *
> - * Return: size of the event on success, <0 on failure
> + * Return: size of the event on success, 0 on failure
>   */
>
>  static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
> --
> 2.23.0
>