linux-kernel - Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry

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Date:   Fri, 19 Jun 2020 13:42:17 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Jerome Forissier <jerome@...issier.org>,
        Maxim Uvarov <maxim.uvarov@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Arnd Bergmann <arnd@...aro.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, peterhuewe@....de
Subject: Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry

On Fri, 19 Jun 2020 at 00:49, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
>
> On Thu, 2020-06-18 at 10:42 +0530, Sumit Garg wrote:
> > On Thu, 18 Jun 2020 at 10:29, Sumit Garg <sumit.garg@...aro.org>
> > wrote:
> [...]
> > > > typedef struct
> > > > {
> > > >         uint32_t timeLow;
> > > >         uint16_t timeMid;
> > > >         uint16_t timeHiAndVersion;
> > > >         uint8_t clockSeqAndNode[8];
> > > > } TEE_UUID;
> > > >
> > > > (GlobalPlatform TEE Internal Core API spec v1.2.1 section 3.2.4)
> > > >
> > > > - The spec does not mandate any particular endianness and simply
> > > > warnsabout possible issues if secure and non-secure worlds differ
> > > > in endianness.
> > > > - OP-TEE uses %pUl assuming that host order is little endian
> > > > (that is true for the Arm platforms that run OP-TEE currently).
> > > > By the same logic %pUl should be fine in the kernel.
> >
> > I think Linux adheres to this RFC [1] for UUID byte order. See below
> > snippet from section: "Layout and Byte Order":
> >
> >    The fields are encoded as 16 octets, with the sizes and order of
> > the
> >    fields defined above, and with each field encoded with the Most
> >    Significant Byte first (known as network byte order).  Note that
> > the
> >    field names, particularly for multiplexed fields, follow
> > historical
> >    practice.
>
> Actually, that's not quite true.  We used to support both little and
> big endian uuids until we realised it was basically microsoft vs
> everyone else (as codified by RFC 4122).  Now we support UUIDs which
> are big endian and GUIDs which are little endian.  This was the commit
> that sorted out the confusion:
>
> commit f9727a17db9bab71ddae91f74f11a8a2f9a0ece6
> Author: Christoph Hellwig <hch@....de>
> Date:   Wed May 17 10:02:48 2017 +0200
>
>     uuid: rename uuid types
>

Thanks for providing the background here.

> so if you're using a little endian uuid, you should probably be using
> GUID for TEE_UUID.

IMO, using GUID in kernel for TEE_UUID in OP-TEE OS will lead to
deviation from GlobalPlatform TEE client spec [1] as the spec only
references it as UUID and we would like to keep kernel TEE client
interface to be compatible with GP specs.

[1] https://globalplatform.org/specs-library/tee-client-api-specification/

-Sumit

>
> James
>