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

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Message-ID: <20190826163020.e7sahr3irqwwneey@linux.intel.com>
Date:   Mon, 26 Aug 2019 19:30:20 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Jones <pjones@...hat.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Bartosz Szczepanek <bsz@...ihalf.com>,
        Lyude Paul <lyude@...hat.com>, linux-efi@...r.kernel.org,
        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 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>

/Jarkko