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

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Date:   Mon, 26 Aug 2019 10:45:35 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Peter Jones <pjones@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Bartosz Szczepanek <bsz@...ihalf.com>,
        Lyude Paul <lyude@...hat.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] efi+tpm: don't traverse an event log with no events

On Mon, Aug 26, 2019 at 9:30 AM Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> On Mon, Aug 26, 2019 at 11:30:28AM -0400, Peter Jones 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@...hat.com>
> > Tested-by: Lyude Paul <lyude@...hat.com>
> > ---
> >  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);
> > +             tbl_size = tpm2_calc_event_log_size(events,
> > +                                                 final_tbl->nr_events,
> > +                                                 log_tbl->log);
> > +     }
>
> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Acked-by: Matthew Garrett <mjg59@...gle.com>