STM32CubeU5 - SBSFU application bug

[tdjastrzebski]

SBSFU app app probably has a bug. Unless tamper detection is disabled in boot_hal_cfg.h file (#define TFM_TAMPER_ENABLE NO_TAMPER), SBSFU_Boot application resets endlessly because FLOW_CONTROL_STEP does not pass evaluation (low_level_security.c file, line 1774).

/* Set active tampers */
if (HAL_RTCEx_SetActiveTampers(&RTCHandle, &sAllTamper) != HAL_OK)
{
    Error_Handler();
}
FLOW_CONTROL_STEP(uFlowProtectValue, FLOW_STEP_TAMP_ACT_EN, FLOW_CTRL_TAMP_ACT_EN); // <-- problem here

The above results in the following serial terminal output:

[tdjastrzebski]

BTW, it probably would be a good idea to add some detailed instruction on how to regress the board and remove protection. On this topic README.md states only: "refer to AN5347". This document describes several methods which may or may not work, depending on the circumstances. It takes some time and frustration to figure out the correct way.

[tdjastrzebski]

I learned that what I described was an expected behavior if CN3 pins 11 & 14 were disconnected. This is meant to demonstrate anti-tamper feature. However, some more descriptive message would be helpful.