linux-kernel - Re: [PATCH v2 1/4] tpm: Add explicit endianness cast

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Message-ID: <CA+zpnLePcFJQURBNZEt=mRSRb9GUYR=1t9EQn82W0+311xKZ7w@mail.gmail.com>
Date:   Thu, 19 Apr 2018 13:09:12 +0000
From:   Thiebaud Weksteen <tweek@...gle.com>
To:     jgg@...pe.ca
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Nayna Jain <nayna@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] tpm: Add explicit endianness cast

On Tue, Apr 17, 2018 at 4:00 PM Jason Gunthorpe <jgg@...pe.ca> wrote:

> On Tue, Apr 17, 2018 at 08:32:33AM +0000, Thiebaud Weksteen wrote:
> > On Tue, Apr 17, 2018 at 5:02 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
> >
> > > On Thu, Apr 12, 2018 at 12:13:47PM +0200, Thiebaud Weksteen wrote:
> > > > Signed-off-by: Thiebaud Weksteen <tweek@...gle.com>
> > > >  drivers/char/tpm/tpm_eventlog_of.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/char/tpm/tpm_eventlog_of.c
> > b/drivers/char/tpm/tpm_eventlog_of.c
> > > > index 96fd5646f866..d74568d58a66 100644
> > > > +++ b/drivers/char/tpm/tpm_eventlog_of.c
> > > > @@ -56,8 +56,8 @@ int tpm_read_log_of(struct tpm_chip *chip)
> > > >        * but physical tpm needs the conversion.
> > > >        */
> > > >       if (of_property_match_string(np, "compatible", "IBM,vtpm") <
0) {
> > > > -             size = be32_to_cpup(sizep);
> > > > -             base = be64_to_cpup(basep);
> > > > +             size = be32_to_cpup((__be32 *)sizep);
> > > > +             base = be64_to_cpup((__be64 *)basep);
> >
> > > Er, no.. change the definitions of sizep and basep to be __be
> >
> > > Jason
> >
> > Please read the comment before the condition. sizep and
> > basep may contain either little endian or big endian and this block is
used
> > to adjust that. Let me know if there is a better way for handling this.

> Well a cast like that will throw sparse warnings, you need __force at
> least

> Jason

I don't think so. Since the variable is only defined as u32*, no specific
warning is generated. I've used `make C=2 drivers/char/tpm/` with this
patch applied and no new warning is being triggered.