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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Mon, 19 Apr 2021 16:40:29 +0300
Message-ID: <CAHp75VeP9eXyrpuWpb9smuLUCBmocwfzA1p4NXPNyNfP0i3ngw@mail.gmail.com>
Subject: Re: [PATCH v1 1/1] tee: optee: Provide special parameter field for
 UUID values
To:     Jens Wiklander <jens.wiklander@linaro.org>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        OP-TEE TrustedFirmware <op-tee@lists.trustedfirmware.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Apr 19, 2021 at 4:30 PM Jens Wiklander
<jens.wiklander@linaro.org> wrote:
> On Mon, Apr 19, 2021 at 2:01 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> >
> > On Mon, Apr 19, 2021 at 01:35:51PM +0200, Jens Wiklander wrote:
> > > On Thu, Apr 15, 2021 at 4:58 PM Andy Shevchenko
> > > <andriy.shevchenko@linux.intel.com> wrote:
> >
> > Thanks for review, my answer below.
> >
> > > >                 struct optee_msg_param_tmem tmem;
> > > >                 struct optee_msg_param_rmem rmem;
> > > >                 struct optee_msg_param_value value;
> > > > +               uuid_t uuid;
> > >
> > > It's nice to get rid of the cast above, but I'm not that keen on the
> > > change in this struct. This file defines the ABI towards Secure world
> > > and adding dependencies on external complex types is a larger problem
> > > than the cast above in my opinion.
> >
> > I understand.
> >
> > So, the cast is simply wrong there. Can you add a comment above that cast to
> > explain that and make it is marked as FIXME? Because there is no guarantee that
> > internal Linux types can be 1:1 mapped to the ABI of something.
>
> We might as well fix it directly instead. How about storing the
> intermediate result in a proper uuid_t and then export it as:
> export_uuid((u8 *)&msg_arg->params[1].u.uuid, &myuuid);

Still a casting here.
With u64 members you have a (potential) endianness issue (consider
BE-32 platform). Also you never know that a b c translates properly to
byte array.

I would rather see a custom function

optee_import_uuid(param, uuid_t *uuid)
{
  u8 uuid_raw[UUID_SIZE];

  put_unaligned_le64(&uuid_raw[0], param.a); // not sure about endianness
  put_unaligned_le64(&uuid_raw[0], param.b); // ditto

  import_uuid();
}

> > What you need, perhaps, is a middle layer function that will copy u64 data
> > to uuid_t or so. Also, u64 is not an ABI type, why the respective __uXX
> > variants are not in use?
>
> Does it make any difference? The file isn't shared with user space and
> I need to sync the file manually anyway since OP-TEE doesn't have the
> same include files.

Yes. It gives a hint that these are ABI (that's why I felt free to add
a member to the union. I have no idea that's an ABI). Optionally a
comment suggesting that.

Besides the above mentioned issues.

-- 
With Best Regards,
Andy Shevchenko