linux-kernel - Re: [PATCH] tpm: fix byte order related arithmetic inconsistency in tpm

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Message-ID: <20170511101646.556aoezp77wlcrw7@intel.com>
Date:   Thu, 11 May 2017 13:16:46 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        tpmdd-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: fix byte order related arithmetic inconsistency in
 tpm_getcap()

On Thu, May 11, 2017 at 01:41:15AM +0200, Luc Van Oostenryck wrote:
> On Wed, May 10, 2017 at 2:34 PM, Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> 
> > Arithmetic should work but it's not a good practice to do additions,
> > substractions or multiplications in any other byte order than the CPU
> > byte order.
> >
> > sparse also complains about this.
> >
> > /Jarkko
> 
> Arithmetic should work?
> let's try with 0x0080:
> in native order: 0x0080 + 0x0080 = 0x0100
> in reverse order: 0x8000 + 0x8000 = 0x0000 != swap16(0x0100)
> 
> Or do I misunderstand what you mean by "arithmetic should work"?
> 
> -- Luc Van Oostenryck

I was referring to the specific code snippet in tpm-interface.c.

/Jarkko