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F28M35H52C: C28 CSM issue - Why unsecure memory can access secure memory

Linda Zhang84708
Expert 6900 points

Part Number: F28M35H52C

Hello Champs,

Customer is using F28M35.

For C28 codes, they programmed the password and also added below settings according to TRM to make sure re-secure:

volatile int *CSMSCR = 0x00AEF; //CSMSCR register

//Set FORCESEC bit

EALLOW;

*CSMSCR = 0x8000;

EDIS;

But they found that executing the codes which were copied from flash into unsecure RAM S0 still can access the functions defined in the codes which were copied from flash into secure RAM L0. They didn't do any unlocking operation and C28 was always in lock status. 

Would you please kindly help? Why can the codes in unsecure memory(RAM S0) access the secure memory? Thanks!

Best Regards,

Linda

  • 0
    TI__Guru** 116081 points

    Hi Linda,

    Would you please kindly help? Why can the codes in unsecure memory(RAM S0) access the secure memory

    What is the meaning of "access" the secure memory here? Is it calling the function which is in secure memory or having read/write access to secure memory. Please note that code in unsecure memory can call a function which is in secure memory. That is allowed. If it's read/write access then I would think it's not secure.

    Regards,

    Vivek Singh 

  • 0 in reply to Vivek Singh
    TI__Expert 6900 points

    Hello Vivek,

    Thank you for your kind help.

    Customer found that code in unsecure memory can call a function which is in secure memory. So this is allowed. Understood.

    As you said " If it's read/write access then I would think it's not secure", does it mean unsecure memory cannot read data from or write data to secure memory if the device is secured? Thanks!

    Best Regards,

    Linda

  • 0 in reply to Linda Zhang84708
    TI__Guru** 116081 points

    As you said " If it's read/write access then I would think it's not secure", does it mean unsecure memory cannot read data from or write data to secure memory if the device is secured? Thanks!

    Correct. Function calls are allowed but READ/WRITE to secure memory by code running from unsecure memory is blocked.

    Regards,

    Vivek Singh

  • 0 in reply to Vivek Singh
    TI__Expert 6900 points

    Hello Vivek,

    It's clear. Thank you so much for your kind help.

    Best Regards,
    Linda