Re: [PATCH] tee: optee: Add SMC for loading OP-TEE image

From: Jens Wiklander
Date: Thu Mar 02 2023 - 02:23:33 EST

On Wed, Mar 1, 2023 at 8:27 PM Jeffrey Kardatzke
<jkardatzke@xxxxxxxxxxxx> wrote:
>
> On Wed, Mar 1, 2023 at 12:44 AM Jens Wiklander
> <jens.wiklander@xxxxxxxxxx> wrote:
> >
> > On Tue, Feb 28, 2023 at 8:29 PM Jeffrey Kardatzke
> > <jkardatzke@xxxxxxxxxxxx> wrote:
> > >
> > > On Tue, Feb 28, 2023 at 10:55 AM Jens Wiklander
> > > <jens.wiklander@xxxxxxxxxx> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Fri, Feb 24, 2023 at 9:17 PM Jeffrey Kardatzke
> > > > <jkardatzke@xxxxxxxxxxxx> wrote:
> > > > >
> > > > > On Fri, Feb 24, 2023 at 12:25 AM Jens Wiklander
> > > > > <jens.wiklander@xxxxxxxxxx> wrote:
> > > > > >
> > > > > > On Thu, Feb 23, 2023 at 8:09 PM Jeffrey Kardatzke
> > > > > > <jkardatzke@xxxxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Thu, Feb 23, 2023 at 1:28 AM Jens Wiklander
> > > > > > > <jens.wiklander@xxxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > On Wed, Feb 22, 2023 at 6:24 PM Jeffrey Kardatzke
> > > > > > > > <jkardatzke@xxxxxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > > Adds an SMC call that will pass an OP-TEE binary image to EL3 and
> > > > > > > > > instruct it to load it as the BL32 payload. This works in conjunction
> > > > > > > > > with a feature added to Trusted Firmware for ARM that supports this.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxxxx>
> > > > > > > > > Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx>
> > > > > > > > > ---
> > > > > > > > >
> > > > > > > > > drivers/tee/optee/Kconfig | 10 +++++
> > > > > > > > > drivers/tee/optee/optee_msg.h | 14 +++++++
> > > > > > > > > drivers/tee/optee/optee_smc.h | 22 ++++++++++
> > > > > > > > > drivers/tee/optee/smc_abi.c | 77 +++++++++++++++++++++++++++++++++++
> > > > > > > > > 4 files changed, 123 insertions(+)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/tee/optee/Kconfig b/drivers/tee/optee/Kconfig
> > > > > > > > > index f121c224e682..5ffbeb3eaac0 100644
> > > > > > > > > --- a/drivers/tee/optee/Kconfig
> > > > > > > > > +++ b/drivers/tee/optee/Kconfig
> > > > > > > > > @@ -7,3 +7,13 @@ config OPTEE
> > > > > > > > > help
> > > > > > > > > This implements the OP-TEE Trusted Execution Environment (TEE)
> > > > > > > > > driver.
> > > > > > > > > +
> > > > > > > > > +config OPTEE_LOAD_IMAGE
> > > > > > > > > + bool "Load Op-Tee image as firmware"
> > > > > > > >
> > > > > > > > OP-TEE
> > > > > > > Done, fixed in next patch set.
> > > > > > > >
> > > > > > > > > + default n
> > > > > > > > > + depends on OPTEE
> > > > > > > > > + help
> > > > > > > > > + This loads the BL32 image for OP-TEE as firmware when the driver is probed.
> > > > > > > > > + This returns -EPROBE_DEFER until the firmware is loadable from the
> > > > > > > > > + filesystem which is determined by checking the system_state until it is in
> > > > > > > > > + SYSTEM_RUNNING.
> > > > > > > > > diff --git a/drivers/tee/optee/optee_msg.h b/drivers/tee/optee/optee_msg.h
> > > > > > > > > index 70e9cc2ee96b..84c1b15032a9 100644
> > > > > > > > > --- a/drivers/tee/optee/optee_msg.h
> > > > > > > > > +++ b/drivers/tee/optee/optee_msg.h
> > > > > > > > > @@ -284,6 +284,20 @@ struct optee_msg_arg {
> > > > > > > > > */
> > > > > > > > > #define OPTEE_MSG_FUNCID_GET_OS_REVISION 0x0001
> > > > > > > > >
> > > > > > > > > +/*
> > > > > > > > > + * Load Trusted OS from optee/tee.bin in the Linux firmware.
> > > > > > > > > + *
> > > > > > > > > + * WARNING: Use this cautiously as it could lead to insecure loading of the
> > > > > > > > > + * Trusted OS.
> > > > > > > > > + * This SMC instructs EL3 to load a binary and excute it as the Trusted OS.
> > > > > > > > > + * The first two params are the high and low 32 bits of the size of the payload
> > > > > > > > > + * and the third and fourth params are the high and low 32 bits of the physical
> > > > > > > > > + * address of the payload. The payload is in the OP-TEE image format.
> > > > > > > > > + *
> > > > > > > > > + * Returns 0 on success and an error code otherwise.
> > > > > > > > > + */
> > > > > > > > > +#define OPTEE_MSG_FUNCID_LOAD_IMAGE 0x0002
> > > > > > > >
> > > > > > > > There's no need to add anything to this file, you can define
> > > > > > > > OPTEE_SMC_FUNCID_LOAD_IMAGE to 2 directly in optee_smc.h below.
> > > > > > > >
> > > > > > > Done, fixed in next patch set.
> > > > > > > > > +
> > > > > > > > > /*
> > > > > > > > > * Do a secure call with struct optee_msg_arg as argument
> > > > > > > > > * The OPTEE_MSG_CMD_* below defines what goes in struct optee_msg_arg::cmd
> > > > > > > > > diff --git a/drivers/tee/optee/optee_smc.h b/drivers/tee/optee/optee_smc.h
> > > > > > > > > index 73b5e7760d10..908b1005e9db 100644
> > > > > > > > > --- a/drivers/tee/optee/optee_smc.h
> > > > > > > > > +++ b/drivers/tee/optee/optee_smc.h
> > > > > > > > > @@ -104,6 +104,28 @@ struct optee_smc_call_get_os_revision_result {
> > > > > > > > > unsigned long reserved1;
> > > > > > > > > };
> > > > > > > > >
> > > > > > > > > +/*
> > > > > > > > > + * Load Trusted OS from optee/tee.bin in the Linux firmware.
> > > > > > > > > + *
> > > > > > > > > + * WARNING: Use this cautiously as it could lead to insecure loading of the
> > > > > > > > > + * Trusted OS.
> > > > > > > > > + * This SMC instructs EL3 to load a binary and excute it as the Trusted OS.
> > > > > > > >
> > > > > > > > execute
> > > > > > > >
> > > > > > > Done, fixed in next patch set.
> > > > > > > > > + *
> > > > > > > > > + * Call register usage:
> > > > > > > > > + * a0 SMC Function ID, OPTEE_SMC_CALL_LOAD_IMAGE
> > > > > > > > > + * a1 Upper 32bit of a 64bit size for the payload
> > > > > > > > > + * a2 Lower 32bit of a 64bit size for the payload
> > > > > > > > > + * a3 Upper 32bit of the physical address for the payload
> > > > > > > > > + * a4 Lower 32bit of the physical address for the payload
> > > > > > > > > + *
> > > > > > > > > + * The payload is in the OP-TEE image format.
> > > > > > > > > + *
> > > > > > > > > + * Returns result in a0, 0 on success and an error code otherwise.
> > > > > > > > > + */
> > > > > > > > > +#define OPTEE_SMC_FUNCID_LOAD_IMAGE OPTEE_MSG_FUNCID_LOAD_IMAGE
> > > > > > > > > +#define OPTEE_SMC_CALL_LOAD_IMAGE \
> > > > > > > > > + OPTEE_SMC_FAST_CALL_VAL(OPTEE_SMC_FUNCID_LOAD_IMAGE)
> > > > > > > > > +
> > > > > > > > > /*
> > > > > > > > > * Call with struct optee_msg_arg as argument
> > > > > > > > > *
> > > > > > > > > diff --git a/drivers/tee/optee/smc_abi.c b/drivers/tee/optee/smc_abi.c
> > > > > > > > > index a1c1fa1a9c28..c1abbee86b39 100644
> > > > > > > > > --- a/drivers/tee/optee/smc_abi.c
> > > > > > > > > +++ b/drivers/tee/optee/smc_abi.c
> > > > > > > > > @@ -8,9 +8,11 @@
> > > > > > > > >
> > > > > > > > > #include <linux/arm-smccc.h>
> > > > > > > > > #include <linux/errno.h>
> > > > > > > > > +#include <linux/firmware.h>
> > > > > > > > > #include <linux/interrupt.h>
> > > > > > > > > #include <linux/io.h>
> > > > > > > > > #include <linux/irqdomain.h>
> > > > > > > > > +#include <linux/kernel.h>
> > > > > > > > > #include <linux/mm.h>
> > > > > > > > > #include <linux/module.h>
> > > > > > > > > #include <linux/of.h>
> > > > > > > > > @@ -1354,6 +1356,77 @@ static void optee_shutdown(struct platform_device *pdev)
> > > > > > > > > optee_disable_shm_cache(optee);
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > +#ifdef CONFIG_OPTEE_LOAD_IMAGE
> > > > > > > > > +
> > > > > > > > > +#define OPTEE_FW_IMAGE "optee/tee.bin"
> > > > > > > > > +
> > > > > > > > > +static int optee_load_fw(struct platform_device *pdev,
> > > > > > > > > + optee_invoke_fn *invoke_fn)
> > > > > > > > > +{
> > > > > > > > > + const struct firmware *fw = NULL;
> > > > > > > > > + struct arm_smccc_res res;
> > > > > > > > > + phys_addr_t data_pa;
> > > > > > > > > + u8 *data_buf = NULL;
> > > > > > > > > + u64 data_size;
> > > > > > > > > + u32 data_pa_high, data_pa_low;
> > > > > > > > > + u32 data_size_high, data_size_low;
> > > > > > > > > + int rc;
> > > > > > > > > +
> > > > > > > > > + rc = request_firmware(&fw, OPTEE_FW_IMAGE, &pdev->dev);
> > > > > > > > > + if (rc) {
> > > > > > > > > + /*
> > > > > > > > > + * The firmware in the rootfs will not be accessible until we
> > > > > > > > > + * are in the SYSTEM_RUNNING state, so return EPROBE_DEFER until
> > > > > > > > > + * that point.
> > > > > > > > > + */
> > > > > > > > > + if (system_state < SYSTEM_RUNNING)
> > > > > > > > > + return -EPROBE_DEFER;
> > > > > > > > > + goto fw_err;
> > > > > > > > > + }
> > > > > > > > > +
> > > > > > > > > + data_size = fw->size;
> > > > > > > > > + /*
> > > > > > > > > + * This uses the GFP_DMA flag to ensure we are allocated memory in the
> > > > > > > > > + * 32-bit space since TF-A cannot map memory beyond the 32-bit boundary.
> > > > > > > > > + */
> > > > > > > > > + data_buf = kmalloc(fw->size, GFP_KERNEL | GFP_DMA);
> > > > > > > > > + if (!data_buf) {
> > > > > > > > > + rc = -ENOMEM;
> > > > > > > > > + goto fw_err;
> > > > > > > > > + }
> > > > > > > > > + memcpy(data_buf, fw->data, fw->size);
> > > > > > > > > + data_pa = virt_to_phys(data_buf);
> > > > > > > > > + reg_pair_from_64(&data_pa_high, &data_pa_low, data_pa);
> > > > > > > > > + reg_pair_from_64(&data_size_high, &data_size_low, data_size);
> > > > > > > > > + goto fw_load;
> > > > > > > > > +
> > > > > > > > > +fw_err:
> > > > > > > > > + pr_warn("image loading failed\n");
> > > > > > > > > + data_pa_high = data_pa_low = data_size_high = data_size_low = 0;
> > > > > > > > > +
> > > > > > > > > +fw_load:
> > > > > > > > > + /*
> > > > > > > > > + * Always invoke the SMC, even if loading the image fails, to indicate
> > > > > > > > > + * to EL3 that we have passed the point where it should allow invoking
> > > > > > > > > + * this SMC.
> > > > > > > > > + */
> > > > > > > > > + invoke_fn(OPTEE_SMC_CALL_LOAD_IMAGE, data_size_high, data_size_low,
> > > > > > > > > + data_pa_high, data_pa_low, 0, 0, 0, &res);
> > > > > > > >
> > > > > > > > Prior to this, you've done nothing to check that the firmware might do
> > > > > > > > what you're expecting. optee_msg_api_uid_is_optee_api() does this
> > > > > > > > under normal circumstances as that SMC function is defined in the SMC
> > > > > > > > Calling Convention. I'm not sure what is the best approach here
> > > > > > > > though.
> > > > > > > >
> > > > > > > The way I think about it is that we have to issue this SMC call once
> > > > > > > we are in the SYSTEM_RUNNING state no matter what. We need to close
> > > > > > > the security hole this would leave open otherwise. Any other checks we
> > > > > > > would do that would prevent us from making that call could be other
> > > > > > > attack vectors.
> > > > > >
> > > > > > This is clearly a weakness in the design. If the kernel config doesn't
> > > > > > match exactly, we either have an open security hole in the secure
> > > > > > world or fail to initialize the driver.
> > > > > Yes, that's correct where if TF-A was built to enable the SMC call,
> > > > > but then the kernel wasn't built to include the OP-TEE driver, or with
> > > > > the image loading SMC config or the driver doesn't get loaded; that's
> > > > > leaving an open security hole. It's understood as part of this design
> > > > > that there's a big open security hole if the system isn't configured
> > > > > properly.
> > > > > > The former can only happen in
> > > > > > systems designed like yours where the kernel up to this point has the
> > > > > > same level of security as the secure world. There's no need for me to
> > > > > > repeat my concerns over that, but this is now going to have an impact
> > > > > > on platforms that don't use your security model too. So far we've
> > > > > > managed to avoid configuration options in the OP-TEE driver that
> > > > > > breaks everything for a class of devices.
> > > > > I could change TF-A and the kernel driver so that if it somebody does
> > > > > enable the kernel option but not the TF-A option, that TF-A returns a
> > > > > specific error code (rather than passing the non-secure originating
> > > > > call to OP-TEE) and the kernel driver can recognize that and then
> > > > > continue as if OP-TEE was loaded. Then enabling this option won't
> > > > > break anything if the TF-A config doesn't match.
> > > >
> > > > Yes, that should help a bit. We may want to check some UUID of the
> > > > service too, just to avoid sending SMCs into the dark and not knowing
> > > > what it may hit. I believe we can sort out those details when
> > > > reviewing the TF-A patch.
> > > >
> > > After looking at the code again...I realize I could do this in TF-A or
> > > OP-TEE. In the current TF-A code (except when this option is enabled),
> > > all SMCs are passed to OP-TEE. So I could add this into the SMC
> > > handling code in OP-TEE to just return success in this case and that's
> > > always enabled (since OP-TEE knows it is already loaded that seems
> > > correct). I'd also want to change the TF-A code so that if it tries to
> > > load OP-TEE more than once, that it returns success to satisfy your
> > > concern about driver reloading if somebody is using this option
> > > (currently it returns -EPERM). Does that sound fine to you?
> >
> > You're overlooking the problem with sending SMCs to an unknown entity.
> > It might not be entirely unknown at this stage due to the entry in
> > DTB, but I would rather not depend on that.
> >
> > Regarding the error code, that can actually be ignored as the driver
> > further down will discover if OP-TEE isn't there, see the call to
> > optee_msg_api_uid_is_optee_api(). The value defined for
> > OPTEE_SMC_CALLS_UID is also defined in the SMC Calling Convention,
> > https://developer.arm.com/documentation/den0028/latest, for this
> > purpose.
> >
>
> OK, now I see what you're getting at regarding the unknown entity. How
> about I first invoke the UID call, and then in TF-A if it is in the
> state where it needs the image loaded still, it then returns an
> alternate UID. In the kernel, if it has the alternate UID, then load
> the OP-TEE image. If it has the usual OP-TEE UID, then just proceed as
> normal. We could even get rid of the kernel config option at that
> point too and always enable this. Would that be fine?

Yes, that's what I had in mind, except that I think it should still be
under a config option, but I don't suppose that's a big deal.

Cheers,
Jens