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

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Date:   Wed, 24 May 2017 09:59:50 -0700
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [tpmdd-devel] [PATCH] tpm: fix byte order related arithmetic
 inconsistency in tpm_getcap()

On Mon, May 15, 2017 at 09:39:34AM -0600, Jason Gunthorpe wrote:
> On Mon, May 15, 2017 at 02:36:02PM +0300, Jarkko Sakkinen wrote:
> > On Wed, May 10, 2017 at 03:34:58PM +0300, Jarkko Sakkinen wrote:
> > > On Tue, May 09, 2017 at 09:13:08AM -0600, Jason Gunthorpe wrote:
> > > > On Tue, May 09, 2017 at 05:13:53PM +0300, Jarkko Sakkinen wrote:
> > > > > On Sun, May 07, 2017 at 08:50:02PM +0300, Jarkko Sakkinen wrote:
> > > > > > You should not do arithmetic with __be32 or __le32 types because
> > > > > > sometimes it results incorrect results. Calculations must be done only
> > > > > > with integers that are in in the CPU byte order. This commit migrates
> > > > > > tpm_getcap() to struct tpm_buf in order to sort out these issues.
> > > > > > 
> > > > > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > > > > > Now this should work as Robertos patches move byte order conversion
> > > > > > where it should be. Sadly I'm out of reach to my Dell E6400 laptop
> > > > > > that I use for TPM 1.2 testing.
> > > > > >  drivers/char/tpm/tpm-interface.c | 30 ++++++++++++++++--------------
> > > > > >  drivers/char/tpm/tpm.h           | 13 -------------
> > > > > >  2 files changed, 16 insertions(+), 27 deletions(-)
> > > > > 
> > > > > I've now tested this with TPM 1.2. Any complains?
> > > > 
> > > > Seems reasonable, but which linke had the problematic arithmetic?
> > > > 
> > > > Jason
> > > 
> > > 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.
> > 
> > Can I get your Reviewed-by for this one?
> 
> Sure, but I'm still wondering what the sparse warning was?
> 
> Jason

This type of errors

drivers/char/tpm//tpm-interface.c:492:42: warning: bad assignment (-=) to restricted __be32

/Jarkko