linux-kernel - Re: [PATCH v1 1/1] tee: optee: Provide special parameter field for UUID values

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Date:   Mon, 19 Apr 2021 16:30:00 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        OP-TEE TrustedFirmware <op-tee@...ts.trustedfirmware.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/1] tee: optee: Provide special parameter field for
 UUID values

On Mon, Apr 19, 2021 at 3:40 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Apr 19, 2021 at 4:30 PM Jens Wiklander
> <jens.wiklander@...aro.org> wrote:
> > On Mon, Apr 19, 2021 at 2:01 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.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@...ux.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

I believe it's a memcpy() we want then, since UUIDs are supposed to be
transmitted using a big endian memory pattern.
We should perhaps add
u8 octets[24];
to that union. Then should the result be well defined using export_uuid().

>
>   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.

It does say that it defines a protocol at the beginning of the file, I
can add ABI too if you think that helps.

Cheers,
Jens