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From:   Masahisa Kojima <masahisa.kojima@linaro.org>
Date:   Wed, 26 Jul 2023 13:49:17 +0900
Message-ID: <CADQ0-X8f7PrhMbepp_SCA3cvrUuz0+t1+xUdhx5O1yijsvMsYQ@mail.gmail.com>
Subject: Re: [PATCH v6 4/4] efivarfs: automatically update super block flag
To:     Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc:     Jan Kiszka <jan.kiszka@siemens.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Jens Wiklander <jens.wiklander@linaro.org>,
        Sumit Garg <sumit.garg@linaro.org>,
        linux-kernel@vger.kernel.org, op-tee@lists.trustedfirmware.org,
        Johan Hovold <johan+linaro@kernel.org>,
        Jeremy Kerr <jk@ozlabs.org>, linux-efi@vger.kernel.org
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Hi Ilias,

On Mon, 24 Jul 2023 at 19:22, Ilias Apalodimas
<ilias.apalodimas@linaro.org> wrote:
>
> Hi Kojima-san,
>
> On Mon, 24 Jul 2023 at 05:53, Masahisa Kojima
> <masahisa.kojima@linaro.org> wrote:
> >
> > Hi Ilias, Jan,
> >
> > On Fri, 23 Jun 2023 at 03:56, Ilias Apalodimas
> > <ilias.apalodimas@linaro.org> wrote:
> > >
> > > Hi Kojima-san, Jan
> > >
> > > On Thu, Jun 22, 2023 at 04:58:50PM +0200, Jan Kiszka wrote:
> > > > On 22.06.23 10:51, Masahisa Kojima wrote:
> > > > > efivar operation is updated when the tee_stmm_efi module is probed.
> > > > > tee_stmm_efi module supports SetVariable runtime service,
> > > > > but user needs to manually remount the efivarfs as RW to enable
> > > > > the write access if the previous efivar operation does not support
> > > > > SerVariable and efivarfs is mounted as read-only.
> > > > >
> > > > > This commit notifies the update of efivar operation to
> > > > > efivarfs subsystem, then drops SB_RDONLY flag if the efivar
> > > > > operation supports SetVariable.
> > > >
> > > > But it does not re-add it and prevents further requests to the TA (that
> > > > will only cause panics there) when the daemon terminates, does it?
> > >
> > > It doesn't, but I think I got a better way out.  Even what you suggest won't
> > > solve the problem entirely.  For the sake of context
> > > - The kernel decides between the RO/RW depending on the SetVariable ptr
> > > - The stmm *module* registers and swaps the RT calls -- and the ptr is now
> > > valid.  Note here that the module probe function will run only if the
> > > supplicant is running
> > > - Once the module is inserted the filesystem will be remounted even without
> > > the supplicant running, which would not trigger an oops, but an hard to
> > > decipher error message from OP-TEE.
> > >
> > > So even if we switch the permissions back to RO when the supplicant dies,
> > > someone can still remount it as RW and trigger the same error.
> > >
> > > Which got me thinking and staring the TEE subsystem a bit more.  The
> > > supplicant is backed by a /dev file, which naturally has .open() and
> > > .release() callbacks.  Why don't we leave the module perform the initial
> > > setup -- e.g talk to StMM and make sure it's there, setup the necessary
> > > buffers etc and defer the actual swapping of the efivar ops and the
> > > filesystem permissions there?  I might 'feel' a bit weird, but as I
> > > mentioned the module probe function only runs if the supplicant is running
> > > anyway
> >
> > I think we are discussing two issues.
> >
>
> Yes
>
> > 1) efivar ops is not restored when the tee-supplicant daemon terminates.
> >
> > The patch[1] sent by Sumit addresses this issue.
> > Thanks to this patch, 'remove' callback of tee_stmm_efi_driver is called
> > when the tee-supplicant daemon terminates, then restore the previous efivar ops
> > and SB_RDONLY flag if necessary.
>
> Ok but that didn't fix the original error Jan reported and I am not
> sure about the patch status

I think the patch is pending because the fTPM still causes panic when the system
shuts down.
https://lore.kernel.org/all/452472c5-ef30-ac30-6e4e-954f53b48315@siemens.com/

This is fTPM specific issue and is unrelated to the tee-based
SetVariable runtime series itself.

>
> >
> > 2) cause panic when someone remounts the efivarfs as RW even if
> > SetVariable is not supported.
>
> Yes, this [0] is fixing that issue

Thank you, I will include this patch in the next submission.

Anyway, the GetVariable() runtime service backed by the U-Boot variable service
does not work from kernel v6.4.0, so I will investigate this issue.

Thanks,
Masahisa Kojima

>
> [0] https://lore.kernel.org/linux-efi/20230609094532.562934-1-ilias.apalodimas@linaro.org/
> Thanks
> /Ilias
> >
> > [1] https://lore.kernel.org/all/20230607151435.92654-1-sumit.garg@linaro.org/
> >
> > Thanks,
> > Masahisa Kojima
> >
> > >
> > > Cheers
> > > /Ilias
> > >
> > > >
> > > > Jan
> > > >
> > > > --
> > > > Siemens AG, Technology
> > > > Competence Center Embedded Linux
> > > >