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

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Message-ID: <CAExDi1RODELLA+N4_5JS3LcDa5DN4q_imYwhw4hd4BHq1GFRBw@mail.gmail.com>
Date:   Thu, 11 May 2017 01:41:15 +0200
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 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