On Mon, Mar 13, 2023 at 6:16 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 ARMv8 and above > architectures that supports this. > > The main purpose of this change is to facilitate updating the OP-TEE > component on devices via a rootfs change rather than having to do a > firmware update. Further details are linked to in the Kconfig file. > > Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxxxx> > Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx> > --- > > Changes in v7: > - Added documentation to Documentation/staging/tee.rst > > Changes in v6: > - Expanded Kconfig documentation > > Changes in v5: > - Renamed config option > - Added runtime warning when config is used > > Changes in v4: > - Update commit message > - Added more documentation > - Renamed config option, added ARM64 dependency > > Changes in v3: > - Removed state tracking for driver reload > - Check UID of service to verify it needs image load > > Changes in v2: > - Fixed compile issue when feature is disabled > - Addressed minor comments > - Added state tracking for driver reload > > Documentation/staging/tee.rst | 41 +++++++++++++++ > drivers/tee/optee/Kconfig | 17 ++++++ > drivers/tee/optee/optee_msg.h | 12 +++++ > drivers/tee/optee/optee_smc.h | 24 +++++++++ > drivers/tee/optee/smc_abi.c | 97 +++++++++++++++++++++++++++++++++++ > 5 files changed, 191 insertions(+) > > diff --git a/Documentation/staging/tee.rst b/Documentation/staging/tee.rst > index 498343c7ab08..315aa8e35e6b 100644 > --- a/Documentation/staging/tee.rst > +++ b/Documentation/staging/tee.rst > @@ -214,6 +214,47 @@ call is done from the thread assisting the interrupt handler. This is a > building block for OP-TEE OS in secure world to implement the top half and > bottom half style of device drivers. > > +OPTEE_INSECURE_LOAD_IMAGE Kconfig option > +---------------------------------------- > + > +The OPTEE_INSECURE_LOAD_IMAGE Kconfig option enables the ability to load the > +BL32 OP-TEE image from the kernel after the kernel boots, rather than loading > +it from the firmware before the kernel boots. This also requires enabling the > +corresponding option in Trusted Firmware for Arm. The documentation there > +explains the security threat associated with enabling this as well as > +mitigations at the firmware and platform level. > +https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html > + > +There are additional attack vectors/mitigations for the kernel that should be > +addressed when using this option. > + > +1. Boot chain security. > + Attack vector: Replace the OP-TEE OS image in the rootfs to gain control of > + the system. > + Migitation: There must be boot chain security that verifies the kernel and > + rootfs, otherwise an attacker can modify the loaded OP-TEE > + binary by modifying it in the rootfs. > +3. Alternate boot modes. > + Attack vector: Using an alternate boot mode (i.e. recovery mode), the OP-TEE > + driver isn't loaded, leaving the SMC hole open. > + Mitigation: If there are alternate methods of booting the device, such as a > + recovery mode, it should be ensured that the same mitigations are > + applied in that mode. > +3. Attacks prior to SMC invocation. > + Attack vector: Code that is executed prior to issuing the SMC call to load > + OP-TEE can be exploited to then load an alternate OS image. > + Mitigation: The OP-TEE driver must be loaded before any potential attack > + vectors are opened up. This should include mounting of any > + modifiable filesystems, opening of network ports or communicating > + with external devices (e.g. USB). > +4. Blocking SMC call to load OP-TEE. > + Attack vector: Prevent the driver from being probed, so the SMC call to load > + OP-TEE isn't executed when desired, leaving it open to being > + executed later and loading a modified OS. > + Mitigation: It is recommended to build the OP-TEE driver as an included > + driver rather than a module to prevent exploits that may cause > + the module to not be loaded. > + > AMD-TEE driver > ============== > > diff --git a/drivers/tee/optee/Kconfig b/drivers/tee/optee/Kconfig > index f121c224e682..70898bbd5809 100644 > --- a/drivers/tee/optee/Kconfig > +++ b/drivers/tee/optee/Kconfig > @@ -7,3 +7,20 @@ config OPTEE > help > This implements the OP-TEE Trusted Execution Environment (TEE) > driver. > + > +config OPTEE_INSECURE_LOAD_IMAGE > + bool "Load OP-TEE image as firmware" > + default n > + depends on OPTEE && ARM64 > + 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. This also requires enabling the corresponding > + option in Trusted Firmware for Arm. The documentation there explains > + the security threat associated with enabling this as well as > + mitigations at the firmware and platform level. > + https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html > + > + Additional documentation on kernel security risks are at > + Documentation/staging/tee.rst. > diff --git a/drivers/tee/optee/optee_msg.h b/drivers/tee/optee/optee_msg.h > index 70e9cc2ee96b..e8840a82b983 100644 > --- a/drivers/tee/optee/optee_msg.h > +++ b/drivers/tee/optee/optee_msg.h > @@ -241,11 +241,23 @@ struct optee_msg_arg { > * 384fb3e0-e7f8-11e3-af63-0002a5d5c51b. > * Represented in 4 32-bit words in OPTEE_MSG_UID_0, OPTEE_MSG_UID_1, > * OPTEE_MSG_UID_2, OPTEE_MSG_UID_3. > + * > + * In the case where the OP-TEE image is loaded by the kernel, this will > + * initially return an alternate UID to reflect that we are communicating with > + * the TF-A image loading service at that time instead of OP-TEE. That UID is: > + * a3fbeab1-1246-315d-c7c4-06b9c03cbea4. > + * Represented in 4 32-bit words in OPTEE_MSG_IMAGE_LOAD_UID_0, > + * OPTEE_MSG_IMAGE_LOAD_UID_1, OPTEE_MSG_IMAGE_LOAD_UID_2, > + * OPTEE_MSG_IMAGE_LOAD_UID_3. > */ > #define OPTEE_MSG_UID_0 0x384fb3e0 > #define OPTEE_MSG_UID_1 0xe7f811e3 > #define OPTEE_MSG_UID_2 0xaf630002 > #define OPTEE_MSG_UID_3 0xa5d5c51b > +#define OPTEE_MSG_IMAGE_LOAD_UID_0 0xa3fbeab1 > +#define OPTEE_MSG_IMAGE_LOAD_UID_1 0x1246315d > +#define OPTEE_MSG_IMAGE_LOAD_UID_2 0xc7c406b9 > +#define OPTEE_MSG_IMAGE_LOAD_UID_3 0xc03cbea4 > #define OPTEE_MSG_FUNCID_CALLS_UID 0xFF01 > > /* > diff --git a/drivers/tee/optee/optee_smc.h b/drivers/tee/optee/optee_smc.h > index 73b5e7760d10..7d9fa426505b 100644 > --- a/drivers/tee/optee/optee_smc.h > +++ b/drivers/tee/optee/optee_smc.h > @@ -104,6 +104,30 @@ 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 execute it as the Trusted OS. > + * > + * 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 2 > +#define OPTEE_SMC_CALL_LOAD_IMAGE \ > + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, ARM_SMCCC_SMC_32, \ > + ARM_SMCCC_OWNER_TRUSTED_OS_END, \ > + 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..00b6b69b6f79 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> > @@ -1149,6 +1151,22 @@ static bool optee_msg_api_uid_is_optee_api(optee_invoke_fn *invoke_fn) > return false; > } > > +#ifdef CONFIG_OPTEE_INSECURE_LOAD_IMAGE > +static bool optee_msg_api_uid_is_optee_image_load(optee_invoke_fn *invoke_fn) > +{ > + struct arm_smccc_res res; > + > + invoke_fn(OPTEE_SMC_CALLS_UID, 0, 0, 0, 0, 0, 0, 0, &res); > + > + if (res.a0 == OPTEE_MSG_IMAGE_LOAD_UID_0 && > + res.a1 == OPTEE_MSG_IMAGE_LOAD_UID_1 && > + res.a2 == OPTEE_MSG_IMAGE_LOAD_UID_2 && > + res.a3 == OPTEE_MSG_IMAGE_LOAD_UID_3) > + return true; > + return false; > +} > +#endif > + > static void optee_msg_get_os_revision(optee_invoke_fn *invoke_fn) > { > union { > @@ -1354,6 +1372,81 @@ static void optee_shutdown(struct platform_device *pdev) > optee_disable_shm_cache(optee); > } > > +#ifdef CONFIG_OPTEE_INSECURE_LOAD_IMAGE > + > +#define OPTEE_FW_IMAGE "optee/tee.bin" > + > +static int optee_load_fw(struct platform_device *pdev, > + optee_invoke_fn *invoke_fn) Please align with the '(' on the line above. > +{ > + 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; > + > + if (!optee_msg_api_uid_is_optee_image_load(invoke_fn)) > + return 0; > + > + 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. > + */ > + pr_warn("OP-TEE image loaded from kernel, this can be insecure"); > + invoke_fn(OPTEE_SMC_CALL_LOAD_IMAGE, data_size_high, data_size_low, > + data_pa_high, data_pa_low, 0, 0, 0, &res); > + if (!rc) > + rc = res.a0; > + if (fw) > + release_firmware(fw); > + kfree(data_buf); > + > + return rc; > +} > +#else > +static inline int optee_load_fw(struct platform_device *__unused1, > + optee_invoke_fn *__unused2) { Please align with the '(' on the line above. The `{` should be at the start of the next line. I'd prefer the normal names of the parameters instead even if they are unused. Cheers, Jens > + return 0; > +} > +#endif > + > static int optee_probe(struct platform_device *pdev) > { > optee_invoke_fn *invoke_fn; > @@ -1372,6 +1465,10 @@ static int optee_probe(struct platform_device *pdev) > if (IS_ERR(invoke_fn)) > return PTR_ERR(invoke_fn); > > + rc = optee_load_fw(pdev, invoke_fn); > + if (rc) > + return rc; > + > if (!optee_msg_api_uid_is_optee_api(invoke_fn)) { > pr_warn("api uid mismatch\n"); > return -EINVAL; > -- > 2.40.0.rc1.284.g88254d51c5-goog >
