[PATCH v4] tee: optee: rework TA bus scanning code

Thu Sep 22 10:51:54 CEST 2022

Hello Patrick and all,

On Mon, 19 Sept 2022 at 16:49, Patrick DELAUNAY
<patrick.delaunay at foss.st.com> wrote:
>
>
> Hi Simon,
>
> On 9/12/22 20:31, Simon Glass wrote:
> > Hi Ilias,
> >
> > On Wed, 7 Sept 2022 at 15:32, Ilias Apalodimas
> > <ilias.apalodimas at linaro.org> wrote:
> >> Hi Simon,
> >>
> >> On Thu, 8 Sept 2022 at 00:11, Simon Glass <sjg at chromium.org> wrote:
> >>> Hi Ilias,
> >>>
> >>> On Tue, 6 Sept 2022 at 15:23, Ilias Apalodimas
> >>> <ilias.apalodimas at linaro.org> wrote:
> >>>> Hi Simon,
> >>>>
> >>>> On Tue, Sep 06, 2022 at 03:18:28PM -0600, Simon Glass wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On Tue, 6 Sept 2022 at 03:37, Ilias Apalodimas
> >>>>> <ilias.apalodimas at linaro.org> wrote:
> >>>>>> Late versions of OP-TEE support a pseudo bus. TAs that behave as
> >>>>>> hardware blocks (e.g TPM, RNG etc) present themselves on a bus
> >>>>>> whichwe can
> >>>>>> scan. Unfortunately U-Boot doesn't support that yet. It's worth
> >>>>>> noting
> >>>>>> that we already have a workaround for RNG. The details are in
> >>>>>> commit 70812bb83da6 ("tee: optee: bind rng optee driver")
> >>>>>>
> >>>>>> So let's add a list of devices based on U-Boot Kconfig options
> >>>>>> that we will
> >>>>>> scan until we properly implement the tee-bus functionality.
> >>>>>>
> >>>>>> While at it change the behaviour of the tee core itself wrt to device
> >>>>>> binding. If some device binding fails, print a warning instead of
> >>>>>> disabling OP-TEE.
> >>>>>>
> >>>>>> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> >>>>>> Reviewed-by: Jens Wiklander <jens.wiklander at linaro.org>
> >>>>>> Reviewed-by: Etienne Carriere <etienne.carriere at linaro.org>
> >>>>>> ---
> >>>>>> Changes since v3:
> >>>>>> - Use NULL instead of a child ptr on device_bind_driver(), since
> >>>>>> it's not
> >>>>>> really needed
> >>>>>> - Changed the style of the optee_bus_probe[] definition to
> >>>>>> {.drv_name = xxx, .dev_name = yyy }
> >>>>>>
> >>>>>> Changes since v2:
> >>>>>> - Fixed typo on driver name ftpm-tee -> ftpm_tee
> >>>>>>
> >>>>>> Changes since v1:
> >>>>>> - remove a macro and use ARRAY_SIZE directly
> >>>>>> drivers/tee/optee/core.c | 24 +++++++++++++++++++-----
> >>>>>> 1 file changed, 19 insertions(+), 5 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c
> >>>>>> index a89d62aaf0b3..c201a4635e6b 100644
> >>>>>> --- a/drivers/tee/optee/core.c
> >>>>>> +++ b/drivers/tee/optee/core.c
> >>>>>> @@ -31,6 +31,18 @@ struct optee_pdata {
> >>>>>> optee_invoke_fn *invoke_fn;
> >>>>>> };
> >>>>>>
> >>>>>> +static const struct {
> >>>>>> + const char *drv_name;
> >>>>>> + const char *dev_name;
> >>>>>> +} optee_bus_probe[] = {
> >>>>>> +#ifdef CONFIG_RNG_OPTEE
> >>>>>> + { .drv_name = "optee-rng", .dev_name = "optee-rng" },
> >>>>>> +#endif
> >>>>>> +#ifdef CONFIG_TPM2_FTPM_TEE
> >>>>>> + { .drv_name = "ftpm_tee", .dev_name = "ftpm_tee" },
> >>>>>> +#endif
> >>>>>> +};
> >>>>>> +
> >>>>>> struct rpc_param {
> >>>>>> u32 a0;
> >>>>>> u32 a1;
> >>>>>> @@ -642,8 +654,7 @@ static int optee_probe(struct udevice *dev)
> >>>>>> {
> >>>>>> struct optee_pdata *pdata = dev_get_plat(dev);
> >>>>>> u32 sec_caps;
> >>>>>> - struct udevice *child;
> >>>>>> - int ret;
> >>>>>> + int ret, i;
> >>>>>>
> >>>>>> if (!is_optee_api(pdata->invoke_fn)) {
> >>>>>> dev_err(dev, "OP-TEE api uid mismatch\n");
> >>>>>> @@ -672,10 +683,13 @@ static int optee_probe(struct udevice *dev)
> >>>>>> * in U-Boot, the discovery of TA on the TEE bus is not supported:
> >>>>>> * only bind the drivers associated to the supported OP-TEETA
> >>>>>> */
> >>>>>> - if (IS_ENABLED(CONFIG_RNG_OPTEE)) {
> >>>>>> - ret = device_bind_driver(dev, "optee-rng", "optee-rng", &child);
> >>>>>> +
> >>>>>> + for (i = 0; i < ARRAY_SIZE(optee_bus_probe); i++) {
> >>>>>> + ret = device_bind_driver(dev, optee_bus_probe[i].drv_name,
> >>>>>> + optee_bus_probe[i].dev_name, NULL);
> >>>>>> if (ret)
> >>>>>> - return ret;
> >>>>>> + dev_warn(dev, "Failed to bind device %s\n",
> >>>>>> + optee_bus_probe[i].dev_name);
> >>>>> Please add device tree nodes for these and all this code can go away.
> >>>> That's the exact opposite of what the commit message describes. OP-TEE
> >>>> supports a scannable bus ifor TAs that behave like hardware blocks and
> >>>> doesn't need a DT entry. Since it's really the TAs compilation decision
> >>>> to support that or not having them as a DT node is not always the right
> >>>> choice.
> >>> This is continuing the perversion of how things are supposed to work
> >>> in driver model.
> >> Which is not the only thing we need to keep in mind though.
> >>
> >>> We need to talk about this because it is simply the wrong way to be
> >>> approaching this.
> >> This is already part of other software components though, e.g it's
> >> already in the kernel. So I don't think it's the wrong approach.
> >>
> >>> There is nothing wrong with putting things in the DT
> >>> and this is how U-Boot works. For now, please create a binding and get
> >>> it reviewed. You don't need all the internal objects but you do need
> >>> an OP-TEE driver and node, as we have with PCI.
> >> Some things *are* working without a DT entry. You had similar
> >> concerns on FF-A (where you requested a DT node again) and people gave
> >> the exact same response. As long as a bus is scanable in any way,
> >> it's preferable to than adding a DT entry. Moreover this code does
> >> not prevent anyone from adding a DT entry.
> >>
> >> To make things even worse if the TA is compiled as 'scanable' and has
> >> a DT entry, it might cause issues down the road when being probed by
> >> the kernel. So really this is just a patch that makes u-boot behave
> >> and plug in properly to the rest of the ecosystem
> > Calling device_bind() is supposed to be used in extremis. I don't see
> > any scanning of an OP-TEE bus here. I just see it binding two child
> > devices which are hard-coded in U-Boot. What am I missing?
>
>
> The tee bus is supported in Linux kernel (each TA have a UUID and
> is discoverable by the TEE driver).
>
> see drivers/tee/optee/core.c::optee_bus_scan()
> and "struct tee_client_driver" with TA UUID
> It wasn't supported in U-Boot is the first TEE/OP-TEE driver implementation
>
> => TA support was hardcoded, under the associated CONFIG
>        and the probe failed when the TA is not present.
>        for example, I add this binding for TA_RNG in drivers/rng/optee_rng.c
>
> The TEE bus feature is added by the Etienne in the serie [1].
> This bus is more flexible and avoid OP-TEE to dynamically modify the
> device tree
> to add/remove the supported SW component (TA support are activated
> during OP-TEE
> compilation) as the binding is managed dynamically in OP-TEE as it is
> done in Linux.
>
> For information, on STM32MP15 platform, I have the trace "can't open
> session:" for
> RNG TA for each 'rng' command when this TA is not supported in OP-TEE but
> OP-TEE RNG driver is activated in U-Boot, because the driver is binding.
>
> [1] drivers: tee: optee: remove unused probe local variable
>
> http://patchwork.ozlabs.org/project/uboot/list/?series=311351&state=*
>
> > This appears to be a Linaro binding, so you should be able to update
> > it easily enough.
> >

Discussing with Patrick, he made a suggestion and showed me I was
wrong in OP-TEE tee-supplicant enumeration constraints in U-Boot.
OP-TEE exposes 2 levels of service discovery, so-called devices
enumeration and device-with-supplicant enumeration. The later are
OP-TEE services that depend on RPC service exposed to OP-TEE by in the
caller OS (U-Boot or Linux kernel). The former are services without
such dependencies. When i posted OP-TEE services discovery in U-Boot,
I made U-Boot to enumerate OP-TEE "devices" (without tee-suppl.
dependencies).
I made it intentionally as U-Boot tee-supplicant does not implement
all OP-TEE RPC services as Linux kernel. Since FTPM TA service relies
on tee-supplicant support, it is not enumerated/discovered.

The point is the U-Boot tee-suppl. does implement the few RPC services
FTPM TA needs (that are memory allocation and RPMB access).
So Patrick argued that U-Boot can as well enumerate OP-TEE service
*with* tee-suppl. devices. The optee ftpm driver can register to this
service discovery and will operate properly.
What puzzled me was that discovery of OP-TEE services that require
tee-suppl. services not available in U-Boot would end in a failure of
the service, but as Patrick rightly said that it makes no sense for
one of add implement u-boot a driver for an OP-TEE service if that
service lacks some U-Boot tee-suppl. supports.

All in one, my apologies Ilias for this mistake. A change in
tee/optee/core.c to also bind services enumerated by OP-TEE command
PTA_CMD_GET_DEVICES_SUPPL should enable full dynamic discovery of
functional FTPM TA service. I'll post a change for that.

Regards,
Etienne

> > Regards,
> > Simon
>
> Regards
> Patrick