write protection mechanism is not working in the internal flash of nrf5340 dk

[SRINI]

Hi ,

My environment :

1. nrf connect sdk
2. nrf5340 dk
3. segger studio IDE

verified method 1:

As per nrf5340 product specification document , we can protect the flash erase and flash write operations using write protection.

CONFIG is a register in NVMC . we can set read only access when set 0 in CONFIG register
NRF_NVMC->CONFIG = 0; // read only access
but, I am able to erase the flash and write the flash. It should not happen.

Verified method 2:

As per below link

docs.zephyrproject.org/.../group__flash__interface_gaf0cda694a08f6bcf230b08790c12b3c2.html

If we want erase the flash and write the flash need to pass false in the second argument to the below function.

flash_write_protection_set(flash_dev, false);

If we want to protect the flash erase and flash write need to pass true in the second argument to the below function .

flash_write_protection_set(flash_dev, true);

but, I am able to erase the flash and write the flash even if pass true in the second argument .

Note : In two methods, I am not able to protect the erase and write operation in the internal flash . please let me know , how can I proceed to use write protection mechanism for block the erase and write flash.

Thanks & Regards,

Srinivas Rao.

[Einar Thorsrud]

Hi Srinivas,

Can you explain in detail how you write protect and then erase, as it is not clear to me exactly what you do.

Also note that the while the CONFIG register of the NVMC can be used to enable or disable flash operations, it can be changed at any time. There are other mechanisms that can be used to provide more protection, such as ACL. I am not sure what your use case and requirements is, though.

Einar

[SRINI]

Method 1:
const struct device *dev;
void erasefunction()    // NVMC header file included in my file.
{
NRF_NVMC->CONFIG = 0; // read only access so, it should not allow to erase or write operation
flash_erase(dev, flash_page_address, 4096); // it will erase the page if write protection disable
}

it should not erase the page why because i have enabled write protection in the above function.

void writefunction()  // NVMC header file included in my file.
{
NRF_NVMC->CONFIG = 0; // read only access so, it should not allow to erase or write operation
flash_write(dev, flash_page_address, buf, 4096); // it will write the page if write protection disable
}

It should not write the page why because I have enabled write protection in the above function.

Method 2:
const struct device *dev;
void erasefunction()
{
flash_write_protection_set(dev, true); // write protection enabled .so, it should not allow to erase or write operation
flash_erase(dev, flash_page_address, 4096); // it will erase the page if write protection disable
}

it should not erase the page why because i have enabled write protection in the above function.

void writefunction()
{
flash_write_protection_set(dev, true); // write protection enabled .so, it should not allow to erase or write operation
flash_write(dev, flash_page_address, buf, 4096); // it will write the page if write protection disable
}

It should not write the page why because I have enabled write protection in the above function.

I hope, you can understand as per above functionality

how can I block the erase and write operations

[Einar Thorsrud]

Hi,

Regarding flash_write_protection_set() that is implemented by flash_nrf_write_protection() zephyr\drivers\flash\soc_flash_nrf.c, and the implementation is empty. So that is not functional. I have not been able to clarify why that is yet.

Regarding writing to the register directly that should work. But note that NRF_NVMC is only relevant for the network core, for the application core you have NRF_NVMC_NS and NRF_NVMC_S.

Also, you you may memory barriers before writing immediately after, so something like this:

NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen; // or NVMC_CONFIG_WEN_Ren or NVMC_CONFIG_WEN_Een
__DSB();
__ISB();

[SRINI]

As per your suggestion, I have updated code as shown in the below . still , I am able to write and erase the page in the flash.

Method 1:
const struct device *dev;
void erasefunction() // NVMC header file included in my file.
{

NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren; // or NVMC_CONFIG_WEN_Wen or NVMC_CONFIG_WEN_Een
__DSB();
__ISB();
flash_erase(dev, flash_page_address, 4096); // it will erase the page if write protection disable
}

it should not erase the page why because i have enabled write protection in the above function.

void writefunction() // NVMC header file included in my file.
{
NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren; // or NVMC_CONFIG_WEN_Wen or NVMC_CONFIG_WEN_Een
__DSB();
__ISB();
flash_write(dev, flash_page_address, buf, 4096); // it will write the page if write protection disable
}

For your information, NRF_NVMC macro defined in the below file

\v1.5.0\zephyr\modules\hal_nordic\nrfx\nrfx_config_nrf5340_application.h 

please let me know the solution for this issue. 

Regards,

Srinivas 

[Einar Thorsrud]

Hi Srinivas,

Can you clarify if you are using the application core or network core, and if using application core if you are building as secure or non-secure?

Einar

[SRINI]

Hi Einar,

I am using application core and building with secure

Regards,

Srinivas 

[Einar Thorsrud]

Hi Srinivas,

I missed an important point before. You are using the flash_erase() function, which is implemented for the nRF in soc_flash_nrf.c. Referring to NCS 1.5.1 you can start at line 268, where you see flash_nrf_api.erase (which is called when you call flash_erase()) is implemented by flash_nrf_erase(). If you follow that further down via some intermediate calls you end up with nrfx_nvmc_page_erase() which is implemented in nrfx_nvmc.c. That calls nvmc_erase_mode_set() which writes to the NVMC_CONFIG registers (both secure and non-secure variants). So in short, it does not matter if you set it before, it will be overwritten by this call.

[SRINI]

Thank you for your available information.