• STM32U585xx option bytes values violation: in case STM32U585xx option bytes values are not correctly
configured to ensure the TOE security, the TOE secure boot procedure after reset detects the problem and
blocks the TOE secure boot procedure execution: Reset is generated, except for the case of RDP option
bytes value for which infinite loop is executed in the secure domain. To unlock the product, STM32U585xx
option bytes must be correctly programmed and the product must be reset.
• PSA APIs violation: Any calls to PSA APIs go through a secure or privilege fix entry point managed by the
TOE. The TOE secure or privileged entry point controls the access to each TF-M Secure Partition, from the
non-secure application or the secure or non-privileged services, by checking the validity of parameters of
any operation requested. Any PSA APIs access violations (secure or privilege) result in an infinite loop in the
secure domain.
• JTAG access violation: Once TOE security is fully configured, the product cannot be debugged via the JTAG
interface anymore:
– With RDP set to Level 2, JTAG connection is only possible to inject OEM2 password and to obtain
device identification, which means any other usage like debug is not possible.
• Tampering attempt: STM32U585xx anti‑tamper mechanisms are activated in the TOE for internal tamper
events on backup voltage domain and cryptographic IP faults. The product is reset in case of any tampering
attempt detected by the TOE.
• RDP regression:
– With the RDP set to level 2 and OEM2 password provisioned, it is possible to do an RDP regression
to level 1 by injecting the OEM2 password on JTAG/SWD interface. Once RDP level 1 is achieved, the
TOE is blocking the boot process and enters an infinite loop in the secure domain, as the verification
of the static protection RDP level is not matching expected RDP level 2 anymore. It is then possible
to perform RDP regression to level 0 which erases all Flash and protected memories (SRAM2 and
back-up registers) and all peripheral registers.
– Any wrong OEM2 password injection on JTAG/SWD interface when RDP is set to level 2 raises an
intrusion signal, blocking access to all protected memories (Flash, protected SRAMs, and back-up
registers).
• Protection against debugging:
– In RDP level 2 with OEM2 password, debug via JTAG is not possible. Nevertheless, with RDP Level
2 with OEM2 password provisioned, it is still possible to go back to RDP level 1 by injecting OEM2
password via JTAG interface, then to RDP level 0. (all memories erased first)
– Intrusion signal raised as soon we connect JTAG, blocking access to all protected memories (Flash,
protected SRAMs, and back-up registers).
4.2.4 Security measures (AGD_OPE.1.6C)
To achieve the TRUSTED_INTEGRATOR, the following measures must be taken:
• Follow all guidelines described and referenced in Section 3.2 Secure installation and secure preparation of
the operational environment (AGD_PRE.1.2C).
• Follow all guidelines described in Section 4.2.1 User‑accessible functions and privileges (AGD_OPE.1.1C)
and Section 4.2.2 Available interfaces and methods of use (AGD_OPE.1.2C and AGD_OPE.1.3C)
regarding the implementation of the required user drivers.
• Once the integrator finishes its IoT device development and wants to start to validate the complete product
with the security fully activated, he must compile the TOE in production mode (that is TFM_DEV_MODE
compilation switch disabled) as stated in Section 3.3 Secure installation to validate the IoT device in the
final security configuration.
• Once the integrator finishes its IoT device development and wants to start the production, the integrator
must securely provision the TOE immutable data specific to the integrator or specific to the product as
stated in section TOE specific information personalization of Section 4.2.1 User‑accessible functions and
privileges (AGD_OPE.1.1C).
• Once the integrator finishes production of a final IoT device, he must set the STM32U585xx hardware static
protections as stated in Section 3.3 Secure installation to disable JTAG interface debug capability (RDP
level2 with OEM2 password) and to lock the STM32U585xx hardware static protections (with RDP Level 2
all option bytes are locked by STM32U585xx hardware).
To achieve TOE_SECRETS, the following measures must be taken:
• The integrator must protect the integrity and confidentiality of the private cryptographic keys used to build
new authentic firmware images.
UM2852
Operational guidance for the integrator role
UM2852 - Rev 1
page 21/27
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