Persistent application data erased upon firmware update using Secure Manager

[CRE]

Hi support team and developper community. Happy new year to all.

I have a project including Secure Manager and a Non-Secure application on a STM32H573 platform.

My non-secure app is modeled after the SMAK_Appli app provided within STM32Cube. I used  HAL_FLASH API to bring flash storage capability to it. 

My application data is stored in a code-free sector at the top of the non-secure flash area, but I could not find any way to notify the Secure Manager about it. Not even in CubeMX. As you would expect, my data persists after reset or power cycle, but it gets erased upon an update of the NS app.

I am aware of the possibility for the Secure Manager to provision data for the sake of the NS application, but this does not fit the bill: my application needs to update the persistent data.

 

So, in a nutshell, how can I implement a persistent storage which survives firmware upgrades ? 

 

Thanks in advance for your support.

CRE

 

[Jocelyn RICARD]

Hello @CRE ,

from your description of your setup, I'm not 100% sure where you are locating these data.

"code-free sector at the top of the non-secure flash area" does not look right though.

In the secure manager configuration, you have this NS reserved area that is made for this purpose. Here below an example where I setup 16KB (2 flash sectors).

These sectors are actually located at end of flash bank1, beginning of flash bank 2.

You can find the details in UM3254 Rev5 chapter 7: Flash memory mapping:

 

So, are you using this NS reserved area ?

Best regards

Jocelyn

 

[CRE]

Hi Jocelyn,

Thanks for your quick answer. I definitely failed to configure this NS reserved area, and consequently, I was storing my data in the NS code area.

However, I do configure it now, as per your example, and I went through all the steps of the How to start with Secure Manager (customized configuration) on STM32H5 wiki. But I keep loosing my data after every firmware update.

In my understanding, my linker config file (STM32H573IIKXQ_FLASH.ld) should automatically be updated by the prebuild script, according to my NS reserved flash area configuration:

 

CODE_SIZE = 0x53*SECTOR_SIZE; /* This define is updated automatically by prebuild command */

RESERVED_AREA_OFFSET = 0x80*SECTOR_SIZE; /* This define is updated automatically by prebuild command */

RESERVED_AREA_SIZE = 0x00*SECTOR_SIZE; /* This define is updated automatically by prebuild command */

 

I would expect RESERVED_AREA_SIZE to increase by 1 (or 2 ?) sectors. and CODE_SIZE to shrink accordingly, as stated by the comment in the file.

but nothing such happens.

And if I manually edit the file and rebuild, I keep erasing my data when updating the app with the YMODEM and image swapping mechanism..

 

FYI, I am using STM32CubeIDE.

Christian