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

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Date:   Fri, 20 Apr 2018 08:57:40 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Thiebaud Weksteen <tweek@...gle.com>
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 Thu, Apr 19, 2018 at 01:09:12PM +0000, Thiebaud Weksteen wrote:
> 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
> 
> 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.

I'm surprised to hear you say that..

Sparse is supposed to require force on all cast that change the
annotation, and there are many examples in the kernel that have force
in that case.

Jason