linux-kernel - Re: [PATCH 3/3] vTPM: support little endian guests

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Date:	Fri, 08 May 2015 19:10:24 -0400
From:	"Hon Ching (Vicky) Lo" <honclo@...ux.vnet.ibm.com>
To:	Ashley Lai <ashley@...leylai.com>
Cc:	tpmdd-devel@...ts.sourceforge.net, Peter Huewe <PeterHuewe@....de>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Vicky Lo <honclo2014@...il.com>, linux-kernel@...r.kernel.org,
	Joy Latten <jmlatten@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/3] vTPM: support little endian guests

Thanks Ashley!

> > The event log in ppc64 arch is always in big endian format. PowerPC
> > supports both little endian and big endian guests. This patch converts
> > the event log entries to guest format.
> 
> I'm a little confused here.  If this patch is to convert the event log 
> entries why are we convert in the conditional statements?  One example 
> below:
> 
> +       if (((convert_to_host_format(event->event_type) == 0) &&
> +            (convert_to_host_format(event->event_size) == 0))
> +           ||
> +           ((v + sizeof(struct tcpa_event) +
> +             convert_to_host_format(event->event_size)) > limit))
> 
> >
> > We defined a macro to convert to guest format. In addition,
> > tpm_binary_bios_measurements_show() is modified to parse the event
> > and print each field individually.
> 

We do not convert the whole event entry.  Instead, we're converting only
what's necessary such as pcr_index, event_type and event_size. pcr_value
and event_data are of type u8.  They do not need LE conversion.


> It's nice to have human readable format but it may break existing tools 
> that parse or understand the machine readable format.  Any comments on 
> this anyone?

I got comments on the format, so I tried to make that conditional
statement all in one line, but the 'Lindent' tool puts the lines back to
the above format..   


Regards,
Vicky

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