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From: Sumit Garg <sumit.garg@linaro.org>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>,
	Jerome Forissier <jerome@forissier.org>,
	Maxim Uvarov <maxim.uvarov@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Arnd Bergmann <arnd@linaro.org>,
	"tee-dev @ lists . linaro . org" <tee-dev@lists.linaro.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	linux-integrity@vger.kernel.org, peterhuewe@gmx.de
Subject: Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry
Date: Mon, 29 Jun 2020 12:25:18 +0530
Message-ID: <CAFA6WYMKbm7HxGf_041JPD+wkjXprB9h+2HgTh4z_Ty97udFSw@mail.gmail.com> (raw)
In-Reply-To: <1593184281.7381.16.camel@HansenPartnership.com>

On Fri, 26 Jun 2020 at 20:41, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
>
> On Fri, 2020-06-26 at 12:29 +0100, Daniel Thompson wrote:
> > On Fri, Jun 26, 2020 at 10:40:41AM +0530, Sumit Garg wrote:
> > > On Fri, 26 Jun 2020 at 05:01, James Bottomley
> > > <James.Bottomley@hansenpartnership.com> wrote:
> > > >
> > > > On Thu, 2020-06-25 at 19:54 +0530, Sumit Garg wrote:
> > > > > On Wed, 24 Jun 2020 at 20:51, James Bottomley
> > > > > <James.Bottomley@hansenpartnership.com> wrote:
> > > > > >
> > > > > > On Wed, 2020-06-24 at 16:17 +0530, Sumit Garg wrote:
> > > > > > > Apologies for delay in my reply as I was busy with some
> > > > > > > other stuff.
> > > > > > >
> > > > > > > On Fri, 19 Jun 2020 at 20:30, James Bottomley
> > > > > > > <James.Bottomley@hansenpartnership.com> wrote:
> > > > > >
> > > > > > [...]
> > > > > > > > it's about consistency with what the kernel types
> > > > > > > > mean.  When some checker detects your using little endian
> > > > > > > > operations on a big endian structure (like in the prink
> > > > > > > > for instance) they're going to keep emailing you about
> > > > > > > > it.
> > > > > > >
> > > > > > > As mentioned above, using different terminology is meant to
> > > > > > > cause more confusion than just difference in endianness
> > > > > > > which is manageable inside TEE.
> > > > > > >
> > > > > > > And I think it's safe to say that the kernel implements
> > > > > > > UUID in big endian format and thus uses %pUb whereas OP-TEE
> > > > > > > implements UUID in little endian format and thus uses %pUl.
> > > > > >
> > > > > > So what I think you're saying is that if we still had uuid_be
> > > > > > and uuid_le you'd use uuid_le, because that's exactly the
> > > > > > structure described in the docs.  But because we renamed
> > > > > >
> > > > > > uuid_be -> uuid_t
> > > > > > uuid_le -> guid_t
> > > > > >
> > > > > > You can't use guid_t as a kernel type because it has the
> > > > > > wrong name?
> > > > >
> > > > > Isn't the rename commit description [1] pretty clear about
> > > > > which is the true UUID type from Linux point of view?
> > > >
> > > > I don't think the kernel code takes a position on eternal verity,
> > > > just on logical or arithmetic truth.  We just have to deal with
> > > > both LE and BE UUIDs so we have appropriate types for them and
> > > > the LE type is now named guid_t.  They're both equally correct to
> > > > use provided the use case matches the designed one. So does the
> > > > name really matter?
> > >
> > > Yes it does. I guess I have provided enough reasoning for that.
> > > Also, the rename commit itself illustrates its importance and
> > > clarifies the use case for which they are meant to be used.
> > >
> > > > If we did
> > > >
> > > > #define uuid_le_t guid_t
> > > >
> > > > would you be happy? (not that the kernel cares about karmic
> > > > emotional states either ...)
> > >
> > > It's not about me being happy but more about confusion and
> > > inconsistency it will bring.
> > >
> > > IMO, either kernel should be opinionated about UUID endianness like
> > > currently it is:
> > >
> > > uuid_t and its corresponding helpers (eg. UUID_INIT) follows BE
> > > format.
> > >
> > > or support both endianness for UUID (no common type: uuid_t) like
> > > we had earlier prior to rename commit:
> > >
> > > uuid_be_t and its corresponding helpers (eg. UUID_BE_INIT) follow
> > > BE format. uuid_le_t and its corresponding helpers (eg.
> > > UUID_LE_INIT) follow LE format.
> > >
> > > But even if we consider later case as well, I am still not sure if
> > > we can switch to uuid_le_t as it's been part of TEE core ABI
> > > (open_session) where UUID is passed in BE format (see LE to BE
> > > conversion in TEE client [1] and vice-versa in OP-TEE OS [2]) and
> > > won't be a backwards compatible change.
> > >
> > > [1] https://github.com/OP-TEE/optee_client/blob/master/libteec/src/
> > > tee_client_api.c#L595
> > > [2] https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/ke
> > > rnel/ree_fs_ta.c#L92
> >
> > I'm struck that all references here are to code that does not run in
> > kernel space. Frankly on LKML I don't know if we should even *care*
> > what format UUIDs are stored in other address spaces.
> >
> > We care about is the endianness of the UUID on the interface
> > boundaries into and out of the kernel[1] and we care that we use the
> > correct kernel type to describe it.
> >
> > I understood from Jerome's post that the UUID that the kernel
> > manipulates are, in fact, big endian and that they should be called
> > uuid_t.
> >
> > Is there more going on here or is that it?
>
> As you say, a UUID to the kernel is a binary blob except for input,
> which to the kernel is INIT_UUID or INIT_GUID and output, which is
> either printk %Ub for uuid_t or %Ul for guid_t.
>
> The bit I objected to was doing a %Ul on a uuid_t because it's going to
> trip the static checkers.

This is exactly which is fixed in v9 patch-set to use %Ub on a uuid_t.

>  That shows me there's a confusion in the
> code between little and big endian UUID types, but I haven't looked
> further than that.

From kernel TEE subsystem perspective, it's all big endian UUID type
which forms the ABI into and out of the kernel.

-Sumit

>
> James
>

  reply index

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 17:58 [PATCHv8 0/3] optee: register drivers on optee bus Maxim Uvarov
2020-06-04 17:58 ` [PATCHv8 1/3] optee: use uuid for sysfs driver entry Maxim Uvarov
2020-06-16 20:50   ` Jarkko Sakkinen
2020-06-17  6:07     ` Sumit Garg
2020-06-17  6:45       ` Maxim Uvarov
2020-06-17 13:58   ` Sumit Garg
2020-06-17 14:12     ` Maxim Uvarov
2020-06-17 15:16     ` [Tee-dev] " Jerome Forissier
2020-06-17 19:52       ` Maxim Uvarov
2020-06-17 20:45         ` Jerome Forissier
2020-06-18  4:59       ` Sumit Garg
2020-06-18  5:12         ` Sumit Garg
2020-06-18 19:18           ` James Bottomley
2020-06-19  8:12             ` Sumit Garg
2020-06-19 15:00               ` James Bottomley
2020-06-24  9:50                 ` Jens Wiklander
2020-06-24 10:47                 ` Sumit Garg
2020-06-24 15:21                   ` James Bottomley
2020-06-24 15:44                     ` Jerome Forissier
2020-06-25 12:51                       ` Maxim Uvarov
2020-06-26  5:13                         ` Sumit Garg
2020-06-26  8:47                           ` Andy Shevchenko
2020-06-26  5:26                         ` Sumit Garg
2020-06-25 14:24                     ` Sumit Garg
2020-06-25 23:31                       ` James Bottomley
2020-06-26  5:10                         ` Sumit Garg
2020-06-26  7:26                           ` Sumit Garg
2020-06-26 11:29                           ` Daniel Thompson
2020-06-26 15:11                             ` James Bottomley
2020-06-29  6:55                               ` Sumit Garg [this message]
2020-06-29  7:03                               ` Jens Wiklander
2020-06-18  6:57         ` Jerome Forissier
2020-06-18  7:44           ` Maxim Uvarov
2020-06-04 17:58 ` [PATCHv8 2/3] optee: enable support for multi-stage bus enumeration Maxim Uvarov
2020-06-16 20:56   ` Jarkko Sakkinen
2020-06-04 17:58 ` [PATCHv8 3/3] tpm_ftpm_tee: register driver on TEE bus Maxim Uvarov
2020-06-16 20:57   ` Jarkko Sakkinen
2020-06-15 14:32 ` [PATCHv8 0/3] optee: register drivers on optee bus Maxim Uvarov
2020-06-16  8:29   ` Jens Wiklander
2020-06-17 14:26     ` Maxim Uvarov
2020-06-18  8:00       ` Jens Wiklander
2020-06-17 23:37     ` Jarkko Sakkinen
2020-06-18  7:56       ` Jens Wiklander
2020-06-23  0:50         ` Jarkko Sakkinen
2020-06-16 20:49   ` Jarkko Sakkinen
2020-06-16 20:54     ` Jarkko Sakkinen

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