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jmcoreymv
Associate II
November 12, 2024
Question

SBSFU not detecting Active Slot Image

  • November 12, 2024
  • 15 replies
  • 2984 views

I'm working on integrating the latest SBSFU (v2.6.2) onto an STM32L4A6 platform. I've reviewed both the user manual and application note for the SBSFU, as well as the examples provided.

In my use case:

  • I have an external attached MMC flash
  • I'm not planning to use the internal MCU flash dual-bank capability (so I can have an image larger than half the 1MB flash size)
  • I don't need rollback/swap capability
  • For OTA updates, my user application will download the encrypted image to a location in the external MMC flash. The SBSFU on boot will check for a valid image in that location, and if so, it will copy it to the MCU flash active slot.

 

I was able to get the B-L475E-IOT01A 2_Images_ExtFlash example to boot and run on my board, and it executes the UserApp.

 

For porting the SBSFU to integrate with my custom UserApp I have:

  • Started from the B-L475E-IOT01A 2_Images_ExtFlash example because it seemed like the closest for what I needed.
  • Replaced the example QSPI driver with an MMC flash driver
  • Modified the various linker files how I think they should be modified based on the user manual/app note.
  • Temporarily disabled all security protections in the SBSFU and enabled verbose debugging
  • The example I started from with external flash was putting the FIREWALL NVDATA section in the middle of the MCU flash (0x8080000) as if we were using dual-bank internal flash, so I changed that by referencing the NUCLEO-L432KC 1_Image example which uses the Firewall but places the NVDATA section at the start of the first active slot (0x8020000).
  • I'm able to build the SECoreBin, SBSFU, and custom UserApp successfuly.
  • When I try to use STMCubeProgrammer to flash the resulting combined binary in to the MCU, it loads but it fails to detect a valid image in Active Slot 1 (the master slot), and then it erases that slot because no valid image was found.
  • I'm having trouble figuring out why it's not seeing a valid image in that location, since it should be part of the combined binary produced by the SBSFU scripts.
    • I've added some trace statements to the when SFU_IMG_DetectFW() is called and more specifically for the SFU_LL_FLASH_INT_Read() function.
    • I can see that when it's searching inside the header region, the se_status returns SE_KO, and the se_ret_status returns SE_ERROR, but I'm not sure how to troubleshoot this further.
    • Here's a console output from some trace logging I've added in this region:

 

SFU_IMG_DetectFW -> slot 1
SFU_LL_FLASH_Read internal
Looking in header
pSource: 0x0x8020000, Length: 320 -> pdest: 0x0x20017e78
DoubleECC_Error_Counter: 0
se_status: 1245757
se_ret_status: 100249
SFU_IMG_DetectFW -> slot 1
SFU_LL_FLASH_Read internal
Looking in header
pSource: 0x0x8020000, Length: 320 -> pdest: 0x0x20017e78
DoubleECC_Error_Counter: 0
se_status: 1245757
se_ret_status: 100249
Slot SLOT_ACTIVE_1 not empty : erasing ...

 

Trying to figure out what my next steps should be to determine why the SBSFU is not finding a valid image in active slot 1.

 

Thanks!

This topic has been closed for replies.

15 replies

Jocelyn RICARD
Jocelyn RICARD
ST Employee
November 13, 2024

Hello @jmcoreymv ,

I don't fully catch what you have done with NVDATA of firewall.

Just be aware that there is a firewall limitation that you can check in errata sheet that impacts the possible mapping solutions.

In any case, my advice will be to debug the modified SBSFU and try to understand what happens.

You can always add SECoreBin symbols to debug inside SECoreBin. Just make sure to disable firewall and once you make it work, re-enable firewall to see if you don't fall in the limitation.

Best regards

Jocelyn

jmcoreymvAuthor
Associate II
November 13, 2024

I'm going to work a bit more on trying to load the SECoreBin symbols to debug that further.  Currently all SBSFU protections are disabled.

Regarding the firewall limitation, could you help me understand this better for my use-case?  I have the STM32L4A6, but I don't want to use the dual-bank capability since it will limit my potential image size to a bit under half of the 1MB flash.  Instead I'm using the external MMC flash as my download slot, and giving up swap/rollback capabilities.

Is this still possible to do?  So firewall would be enabled, code and NV data would be protected, but I don't want to place NVDATA in the middle of the MCU flash because that would prevent me from supporting larger images.  Is my understanding correct?

Jocelyn RICARD
Jocelyn RICARD
ST Employee
November 22, 2024

Hello @jmcoreymv ,

I tried changing the L475 configuration to align to your requierements.

I faced an issue, maybe the same as yours.

The crypto used is mbedTLS on this example. It is consuming lots of memory.

The SE_SP_SMUGGLE is the entry leads to se_callgate. You should have entered inside.

By debugging, I could see that signature verification returned -16 meaning lack of memory.

So, I increased the heap size of the secure engine, adapted the mapping_sbsfu.ld to provide more memory to secure engine. And it passed.

Now, I disabled firewall for now just to check things are working.

Here are the changes I made:

In mapping_fwimg.ld: 

__ICFEDIT_SLOT_Active_1_header__ = 0x08014000;
__ICFEDIT_SLOT_Active_1_start__ = 0x08015000;
__ICFEDIT_SLOT_Active_1_end__ = 0x080FFFFF;

/* Dwl slot #1 (472 kbytes) */
__ICFEDIT_SLOT_Dwl_1_start__ = 0x90000000;
__ICFEDIT_SLOT_Dwl_1_end__ = 0x900EAFFF;

 

Header is just after the SBSFU

in sfu_low_level_security.h

#define SFU_PROTECT_FWALL_NVDATA_ADDR_START ((uint32_t)(SB_REGION_ROM_END + 1))/*!< Firewall protection NVDATA
 area START address*/
#define SFU_PROTECT_FWALL_NVDATA_SIZE (SLOT_ACTIVE_1_HEADER)/*!< Firewall protection NVDATA area

 

Add more side for SE Heap

_Min_Heap_Size = 0x1800;

 

And in mapping_sbsfu.ld

__ICFEDIT_SE_region_RAM_end__ = 0x20003DFF;

 

I could make an update from external flash.

Now, I will need to reactivate firewall protection. May need to change some mappings.

Best regards

Jocelyn

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