linux-kernel - Re: [tpmdd-devel] [PATCH 1/3] vTPM: fixed the limit checking

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Date:	Tue, 12 May 2015 16:19:12 -0500
From:	"Joy M. Latten" <jmlatten@...ux.vnet.ibm.com>
To:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:	"Hon Ching(Vicky) Lo" <honclo@...ux.vnet.ibm.com>,
	tpmdd-devel@...ts.sourceforge.net,
	Ashley Lai <ashley@...leylai.com>,
	linux-kernel@...r.kernel.org, Peter Huewe <PeterHuewe@....de>
Subject: Re: [tpmdd-devel] [PATCH 1/3] vTPM: fixed the limit checking

Hi Stefan,

On Mon, 2015-05-11 at 09:02 -0400, Stefan Berger wrote: 
> On 05/05/2015 08:51 PM, Hon Ching(Vicky) Lo wrote:
> > Do not skip the last entry of the event log.
> >
> > Signed-off-by: Hon Ching(Vicky) Lo <honclo@...ux.vnet.ibm.com>
> > Signed-off-by: Joy Latten <jmlatten@...ux.vnet.ibm.com>
> >
> > Changelog:
> > - remove redundant code
> > ---
> >   drivers/char/tpm/tpm_eventlog.c |    5 +----
> >   1 files changed, 1 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/char/tpm/tpm_eventlog.c b/drivers/char/tpm/tpm_eventlog.c
> > index 3a56a13..e77d8c1 100644
> > --- a/drivers/char/tpm/tpm_eventlog.c
> > +++ b/drivers/char/tpm/tpm_eventlog.c
> > @@ -116,11 +116,8 @@ static void *tpm_bios_measurements_next(struct seq_file *m, void *v,
> >
> >   	event = v;
> >
> > -	if (event->event_type == 0 && event->event_size == 0)
> > -		return NULL;
> > -
> >   	if ((event->event_type == 0 && event->event_size == 0) ||
> > -	    ((v + sizeof(struct tcpa_event) + event->event_size) >= limit))
> > +	    ((v + sizeof(struct tcpa_event) + event->event_size) > limit))
> >   		return NULL;
> >
> >   	(*pos)++;
> 
> The limit stems from log->bios_event_log_end and is calculated as follows:
> 
>   log->bios_event_log_end = log->bios_event_log + len;
> 
> The '>=' above is correct since the limit address itself is not part of 
> the log anymore.
> 
> The log is the following sequence of addresses:
> 
> [log->bios_event_log ... log->bios_event_log + len - 1 ]
> 
> or
> 
> [log->bios_event_log ... log->bios_event_log + len [
> 
> with ']' meaning inclusive and '[' meaning exclusive.
> 
Thanks for pointing this out... you are correct.
We are just seeing where the spec describes this.

On powerpc(p8/powervm)) using vtpm, the last entry doesn't
get shown when ">=", so I suspect phype may be giving us
an "inclusive" len. Vicky and I will investigate this.

regards,
Joy



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