ST X-CUBE-SBSFU, Руководство пользователя, Страница: 24 / 94

Protection measures and security strategy UM2262
24/94 UM2262 Rev 6
•
PCROP
(1)
(proprietary code readout protection): a section of Flash is defined as
execute-only applying PCROP protection on it: it is not possible to access this section
in reading nor writing. Being an execute-only area, a key is protected with PCROP only
if it is "embedded" in a piece of code: executing this code moves the key to a specific
pointer in RAM. Placed behind the firewall, its execution is not possible from outside.
•
WRP (write protection): write protection is used to protect trusted code from external
attacks or even internal modifications such as unwanted writings/erase operations on
critical code/data.
•
MPU (memory protection unit): the MPU is used to make an embedded system more
robust by splitting the memory map for Flash and SRAMs into regions having their own
access rights. In the SBSFU application example, MPU is configured in order to ensure
that no other code is executed from any memories during SBSFU code execution.
When leaving the SBSFU application, the MPU configuration is updated to authorize
also the execution of user application code.
1. For the STM32L0 Series, read protection is tightly coupled with write protection: when activated, any read-
protected sector is also write-protected. For this reason, read protection cannot be activated.
5.2 STM32F4 Series, STM32F7 Series and STM32L1 Series
Figure 7 illustrates how the system, the code, and the data are protected in the
X-CUBE-SBSFU application example for the STM32F4 Series, STM32F7 Series, and
STM32L1 Series.
Figure 7. STM32F4, STM32F7 and STM32L1 protection overview during SBSFU execution