Re: [PATCH RFC 3/3] tee: introduce orphan tee_shm and default context

[Sumit Garg]

On Tue, 26 Nov 2024 at 14:03, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
>
> On Mon, Nov 25, 2024 at 9:55 PM Amirreza Zarrabi
> <quic_azarrabi@xxxxxxxxxxx> wrote:
> >
> >
> >
> > On 11/25/2024 6:51 PM, Sumit Garg wrote:
> > > On Mon, 25 Nov 2024 at 12:53, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> > >>
> > >> On Mon, Nov 25, 2024 at 7:14 AM Sumit Garg <sumit.garg@xxxxxxxxxx> wrote:
> > >>>
> > >>> On Mon, 25 Nov 2024 at 03:00, Amirreza Zarrabi
> > >>> <quic_azarrabi@xxxxxxxxxxx> wrote:
> > >>>>
> > >>>>
> > >>>> Hi Sumit,
> > >>>>
> > >>>> Thank you so much for the comemnts :).
> > >>>>
> > >>>> On 11/23/2024 9:32 PM, Sumit Garg wrote:
> > >>>>> Hi Amirreza,
> > >>>>>
> > >>>>> Thanks for proposing this.
> > >>>>>
> > >>>>> On Fri, 22 Nov 2024 at 06:38, Amirreza Zarrabi
> > >>>>> <quic_azarrabi@xxxxxxxxxxx> wrote:
> > >>>>>>
> > >>>>>>
> > >>>>>> On 11/21/2024 11:08 PM, Jens Wiklander wrote:
> > >>>>>>
> > >>>>>> Hi Jens,
> > >>>>>>
> > >>>>>>> Hi Amirreza,
> > >>>>>>>
> > >>>>>>> On Thu, Nov 21, 2024 at 2:37 AM Amirreza Zarrabi
> > >>>>>>> <quic_azarrabi@xxxxxxxxxxx> wrote:
> > >>>>>>>>
> > >>>>>>>> The default context has a lifespan similar to the tee_device.
> > >>>>>
> > >>>>> Since it's associated with tee_device context, let's call it obvious
> > >>>>> via renaming it as device context instead (s/def_ctx/dev_ctx/ in this
> > >>>>> patch).
> > >>>>>
> > >>>>
> > >>>> Make sense, I'll rename it.
> > >>>>
> > >>>>>>>> It is used as a context for shared memory if the context to which the
> > >>>>>>>> shared memory belongs is released, making the tee_shm an orphan.
> > >>>>>>>> This allows the driver implementing shm_unregister to safely make
> > >>>>>>>> subsequent calls, such as to a supplicant if needed.
> > >>>>>>>>
> > >>>>>>>> It also enables users to free the shared memory while the driver is
> > >>>>>>>> blocked on unregister_tee_device safely.
> > >>>>>>>>
> > >>>>>>>> Preferably, this should be used for all driver internal uses, using
> > >>>>>>>> teedev_get_def_context rather than calling teedev_open.
> > >>>>>
> > >>>>> Makes sense to me.
> > >>>>>
> > >>>>>>>>
> > >>>>>>>> Signed-off-by: Amirreza Zarrabi <quic_azarrabi@xxxxxxxxxxx>
> > >>>>>>>> ---
> > >>>>>>>>  drivers/tee/optee/core.c    |  2 +-
> > >>>>>>>>  drivers/tee/optee/ffa_abi.c |  2 +-
> > >>>>>>>>  drivers/tee/optee/smc_abi.c |  2 +-
> > >>>>>>>>  drivers/tee/tee_core.c      | 83 +++++++++++++++++++++++++++++----------------
> > >>>>>>>>  drivers/tee/tee_private.h   |  3 --
> > >>>>>>>>  drivers/tee/tee_shm.c       | 18 ++--------
> > >>>>>>>>  include/linux/tee_core.h    | 15 ++++++++
> > >>>>>>>>  include/linux/tee_drv.h     |  7 ----
> > >>>>>>>>  8 files changed, 73 insertions(+), 59 deletions(-)
> > >>>>>>>>
> > >>>>>>>> diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c
> > >>>>>>>> index c75fddc83576..78d43d0c8014 100644
> > >>>>>>>> --- a/drivers/tee/optee/core.c
> > >>>>>>>> +++ b/drivers/tee/optee/core.c
> > >>>>>>>> @@ -173,7 +173,7 @@ void optee_remove_common(struct optee *optee)
> > >>>>>>>>
> > >>>>>>>>         optee_notif_uninit(optee);
> > >>>>>>>>         optee_shm_arg_cache_uninit(optee);
> > >>>>>>>> -       teedev_close_context(optee->ctx);
> > >>>>>>>> +
> > >>>>>>>>         /*
> > >>>>>>>>          * The two devices have to be unregistered before we can free the
> > >>>>>>>>          * other resources.
> > >>>>>>>> diff --git a/drivers/tee/optee/ffa_abi.c b/drivers/tee/optee/ffa_abi.c
> > >>>>>>>> index f3af5666bb11..6ad94f0788ad 100644
> > >>>>>>>> --- a/drivers/tee/optee/ffa_abi.c
> > >>>>>>>> +++ b/drivers/tee/optee/ffa_abi.c
> > >>>>>>>> @@ -949,7 +949,7 @@ static int optee_ffa_probe(struct ffa_device *ffa_dev)
> > >>>>>>>>         optee_shm_arg_cache_init(optee, arg_cache_flags);
> > >>>>>>>>         mutex_init(&optee->rpmb_dev_mutex);
> > >>>>>>>>         ffa_dev_set_drvdata(ffa_dev, optee);
> > >>>>>>>> -       ctx = teedev_open(optee->teedev);
> > >>>>>>>> +       ctx = teedev_get_def_context(optee->teedev);
> > >>>>>>>>         if (IS_ERR(ctx)) {
> > >>>>>>>>                 rc = PTR_ERR(ctx);
> > >>>>>>>>                 goto err_rhashtable_free;
> > >>>>>>>> diff --git a/drivers/tee/optee/smc_abi.c b/drivers/tee/optee/smc_abi.c
> > >>>>>>>> index e9456e3e74cc..c77a3e631d04 100644
> > >>>>>>>> --- a/drivers/tee/optee/smc_abi.c
> > >>>>>>>> +++ b/drivers/tee/optee/smc_abi.c
> > >>>>>>>> @@ -1722,7 +1722,7 @@ static int optee_probe(struct platform_device *pdev)
> > >>>>>>>>         mutex_init(&optee->rpmb_dev_mutex);
> > >>>>>>>>
> > >>>>>>>>         platform_set_drvdata(pdev, optee);
> > >>>>>>>> -       ctx = teedev_open(optee->teedev);
> > >>>>>>>> +       ctx = teedev_get_def_context(optee->teedev);
> > >>>>>>>>         if (IS_ERR(ctx)) {
> > >>>>>>>>                 rc = PTR_ERR(ctx);
> > >>>>>>>>                 goto err_supp_uninit;
> > >>>>>>>> diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> > >>>>>>>> index 93f3b330aec8..805e1336089d 100644
> > >>>>>>>> --- a/drivers/tee/tee_core.c
> > >>>>>>>> +++ b/drivers/tee/tee_core.c
> > >>>>>>>> @@ -57,7 +57,6 @@ struct tee_context *teedev_open(struct tee_device *teedev)
> > >>>>>>>>                 goto err;
> > >>>>>>>>         }
> > >>>>>>>>
> > >>>>>>>> -       kref_init(&ctx->refcount);
> > >>>>>>>>         ctx->teedev = teedev;
> > >>>>>>>>         INIT_LIST_HEAD(&ctx->list_shm);
> > >>>>>>>>         rc = teedev->desc->ops->open(ctx);
> > >>>>>>>> @@ -73,36 +72,43 @@ struct tee_context *teedev_open(struct tee_device *teedev)
> > >>>>>>>>  }
> > >>>>>>>>  EXPORT_SYMBOL_GPL(teedev_open);
> > >>>>>>>>
> > >>>>>>>> -void teedev_ctx_get(struct tee_context *ctx)
> > >>>>>>>> +struct tee_context *teedev_get_def_context(struct tee_device *teedev)
> > >>>>>>>>  {
> > >>>>>>>> -       if (ctx->releasing)
> > >>>>>>>> -               return;
> > >>>>>>>> +       int rc;
> > >>>>>>>> +       struct tee_context *ctx = &teedev->def_ctx;
> > >>>>>>>>
> > >>>>>>>> -       kref_get(&ctx->refcount);
> > >>>>>>>> -}
> > >>>>>>>> +       ctx->teedev = teedev;
> > >>>>>>>> +       INIT_LIST_HEAD(&ctx->list_shm);
> > >>>>>>>> +       rc = teedev->desc->ops->open(ctx);
> > >>>>>>>> +       if (rc)
> > >>>>>>>> +               return ERR_PTR(rc);
> > >>>>>>>
> > >>>>>>> I think ctx->teedev and ctx->list_shm must always be initialized or
> > >>>>>>> &teedev->def_ctx can't be used in teedev_close_context().
> > >>>>>>
> > >>>>>> True, but &teedev->def_ctx is never used in teedev_close_context().
> > >>>>>> The closing of the &teedev->def_ctx simply ignored. So once opened,
> > >>>>>> &teedev->def_ctx will always remain open until the tee_device is alive.
> > >>>>>>
> > >>>>>>> We could initialize teedev->def_ctx on the first call to teedev_open()
> > >>>>>>> on that tee_device. We need a way to tell the
> > >>>>>>> teedev->desc->ops->open() to the backed driver that it's initializing
> > >>>>>>> the default context though, or optee_open() can't handle the
> > >>>>>>> tee-supplicant case properly.
> > >>>>>>>
> > >>>>>>
> > >>>>>> That's a good point. This way, it is guaranteed that there is one def_ctx
> > >>>>>> per teedev. There should be a way to tell the open() callback that it is
> > >>>>>> a def_ctx, so it is not registered as a supplicant context.
> > >>>>>>
> > >>>>>>
> > >>>>>>> Should we allow this function to be called more than once for each teedev?
> > >>>>>>
> > >>>>>> Yes, moving to teedev_open() will fix the issue.
> > >>>>>>
> > >>>>>>> Do we need serialization in this function if it's called after the
> > >>>>>>> driver is probed?
> > >>>>>>>
> > >>>>>>
> > >>>>>> True. I'll make sure there is no race.
> > >>>>>>
> > >>>>>>>>
> > >>>>>>>> -static void teedev_ctx_release(struct kref *ref)
> > >>>>>>>> -{
> > >>>>>>>> -       struct tee_context *ctx = container_of(ref, struct tee_context,
> > >>>>>>>> -                                              refcount);
> > >>>>>>>> -       ctx->releasing = true;
> > >>>>>>>> -       ctx->teedev->desc->ops->release(ctx);
> > >>>>>>>> -       kfree(ctx);
> > >>>>>>>> +       return ctx;
> > >>>>>>>>  }
> > >>>>>>>> +EXPORT_SYMBOL_GPL(teedev_get_def_context);
> > >>>>>>>>
> > >>>>>>>> -void teedev_ctx_put(struct tee_context *ctx)
> > >>>>>>>> +void teedev_close_context(struct tee_context *ctx)
> > >>>>>>>>  {
> > >>>>>>>> -       if (ctx->releasing)
> > >>>>>>>> +       struct tee_device *teedev = ctx->teedev;
> > >>>>>>>> +       struct tee_shm *shm;
> > >>>>>>>> +
> > >>>>>>>> +       if (ctx == &teedev->def_ctx)
> > >>>>>>>>                 return;
> > >>>>>>>>
> > >>>>>>>> -       kref_put(&ctx->refcount, teedev_ctx_release);
> > >>>>>>>> -}
> > >>>>>>>> +       teedev->desc->ops->release(ctx);
> > >>>>>>>>
> > >>>>>>>> -void teedev_close_context(struct tee_context *ctx)
> > >>>>>>>> -{
> > >>>>>>>> -       struct tee_device *teedev = ctx->teedev;
> > >>>>>>>> +       mutex_lock(&teedev->mutex);
> > >>>>>>>> +       list_for_each_entry(shm, &ctx->list_shm, link) {
> > >>>>>>>> +               /* Context released. However, shm still holding a teedev reference.
> > >>>>>>>> +                * Replace shm->ctx with the default context so that tee_shm_get_from_id()
> > >>>>>>>> +                * fails (i.e. it is not accessible from userspace) but shm still
> > >>>>>>>> +                * holds a valid context for further clean up, e.g. shm_unregister().
> > >>>>>>>> +                */
> > >>>>>>>
> > >>>>>>> /*
> > >>>>>>>  * Please format
> > >>>>>>>  * multiline comments
> > >>>>>>>  * like this. Please
> > >>>>>>>  * keep the lines at
> > >>>>>>>  * max 80 columns
> > >>>>>>>  * here and at other
> > >>>>>>>  * places in the patch-
> > >>>>>>>  * set.
> > >>>>>>>  */
> > >>>>>>>
> > >>>>>>
> > >>>>>> Ack.
> > >>>>>>
> > >>>>>>>> +               shm->ctx = &teedev->def_ctx;
> > >>>>>>>
> > >>>>>>> shm->ctx will always point to a valid context, even if it is the
> > >>>>>>> default context. It seems that we can always get hold of the correct
> > >>>>>>> teedev via shm->ctx->teedev. Do we need "tee: revert removal of
> > >>>>>>> redundant teedev in struct tee_shm"?
> > >>>>>>>
> > >>>>>>
> > >>>>>> It was there in case we wanted to use NULL, but with def_ctx, it is not
> > >>>>>> necessary. I am withdrawing that commit. :).
> > >>>>>>
> > >>>>>>> Shouldn't the shm be removed from the ctx->list_shm and be moved to
> > >>>>>>> teedev->def_ctx.list_shm?
> > >>>>>
> > >>>>> +1
> > >>>>>
> > >>>>
> > >>>> Ack.
> > >>>>
> > >>>>>>>
> > >>>>>>
> > >>>>>> Not really. If we put shm in the teedev->def_ctx.list_shm, by the time
> > >>>>>> we are closing the def_ctx, the list is guaranteed to be empty.
> > >>>>>>
> > >>>>>> However, I understand it is cleaner and more consistent to do that rather
> > >>>>>> than making changes to tee_shm_put().
> > >>>>>>
> > >>>>>> I'll do it.
> > >>>>>>
> > >>>>>>>> +       }
> > >>>>>>>> +       mutex_unlock(&teedev->mutex);
> > >>>>>>>>
> > >>>>>>>> -       teedev_ctx_put(ctx);
> > >>>>>>>> +       kfree(ctx);
> > >>>>>>>>         tee_device_put(teedev);
> > >>>>>>>>  }
> > >>>>>>>>  EXPORT_SYMBOL_GPL(teedev_close_context);
> > >>>>>>>> @@ -946,6 +952,8 @@ struct tee_device *tee_device_alloc(const struct tee_desc *teedesc,
> > >>>>>>>>
> > >>>>>>>>         teedev->desc = teedesc;
> > >>>>>>>>         teedev->pool = pool;
> > >>>>>>>> +       /* Only open default context when teedev_get_def_context() called. */
> > >>>>>>>> +       teedev->def_ctx.teedev = NULL;
> > >>>>>
> > >>>>> Why don't you open the device context here only? This will associate
> > >>>>> it automatically with teedev lifespan and then
> > >>>>> teedev_get_def_context() will just return a reference to that.
> > >>>>>
> > >>>>> -Sumit
> > >>>>>
> > >>>>
> > >>>> So my assumption is that the tee_devic_alloc() is called as part of
> > >>>> the driver initialization; there is no guarantee that at this time the
> > >>>> driver is actually ready to accept any open() callback.
> > >>>>
> > >>>
> > >>> The drivers should be able to handle open() callback since we already
> > >>> check for !teedesc->ops->open in the beginning of tee_devic_alloc().
> > >>> Also, we need to open a device context for !TEE_DESC_PRIVILEGED such
> > >>> that we don't open a supplicant device context there.
> > >>
> > >> It would be nice to have the device context fully initialized when the
> > >> probe function returns. How about adding a "bool is_dev_ctx" to struct
> > >> tee_context so the open() callback can tell that this is a special
> > >> tee_contex?
> > >
> > > Sure, that will be useful to distinguish the device context from
> > > normal client context.
> > >
> > > -Sumit
> > >
> >
> > So, as far as the open() callback, I do not believe checking if it is not null
> > is reasonable for calling it here. Most drivers allocate resources and then
> > initialize them. So, assume these steps for a TEE driver:
> >  (1) allocate internal data structures,
> >  (2) allocate the device,
> >  (3) initialize the internal data structurse and then
> >  (4) register the device.
> >
> > Having these steps for a backend driver means that if you call open() at
> > step (2), the internal data structures are not ready.

As part of tee_device_alloc(), every driver has to pass "const struct
tee_desc *teedesc" fully initialized. Which internal data structures
are you referring too? Is there any upstream example?

> >
> > I was originally thinking of going with Jens' suggestion to open dev_ctx in
> > the teedev_open(), and use a flag to distinguish the type of context for
> > the open() callback
> >
> > What about this:
> > Open the dev_ctx in the tee_device_register(), at the last step before
> > setting the TEE_DEVICE_FLAG_REGISTERED flag. Then the open() callback can
> > check for this flag to determine if it is a normal context or dev_ctx.
> > If the open() is called while the device has not been registered, it should
> > handle it differently
>
> That makes sense, the driver should be prepared to handle open() calls
> after tee_device_register() anyway.
> However, there is no serialization of the flags field in struct
> tee_device. Hmm, would it be too hacky for the open() callback to
> check if &ctx->teedev.dev_ctx == ctx? We could add a helper function
> to wrap that check.
>

Your suggested change requires every driver to update open() callback
and later other callbacks may have to support it too. IMHO, only
teedev_get_dev_ctx() should be able to return a reference to device
context for usage within the TEE and the implementation driver.

I am still not able to understand why the following won't work with a
clear lifetime for the device context?

tee_device_alloc()
  -> if (!(teedesc->flags & TEE_DESC_PRIVILEGED))
desc->ops->open(&teedev->dev_ctx);

tee_device_put()
  -> if (teedev->dev_ctx) desc->ops->release(&teedev->dev_ctx);

-Sumit

> Cheers,
> Jens
>
> >
> > - Amir
> >
> > >>
> > >> Cheers,
> > >> Jens
> > >>
> > >>>
> > >>> -Sumit