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TMS320F28035：Will the registers be locked when using CSM encryption?

Julia Li
Expert 4405 points
Part Number: TMS320F28035
Other Parts Discussed in Thread: UNIFLASH

Hello Champs,

We know that CSM prevents access/visibility to on-chip memory to unauthorized person. The CSM of F28035 can secure Flash and RAM. Does it mean that it also locks all registers at the same time, so that the registers cannot be modified?

Best Regards,

Julia

  • 0
    TI__Guru* 95315 points

    Julia,

          When the device is secure, access to secure resources is blocked by the CSM. Registers can still be modified by the code running out of secure memory.

  • 0 in reply to Hareesh Janakiraman
    TI__Guru* 95315 points

    Julia,

                Upon some reflection, this appears to be a nuanced question. I think this is what you are asking: In a secure device, will I be able to modify the value of a register, which is not protected by the CSM? If so, answer is below:

    Any access to a protected resource (like Flash or secure RAM blocks) would activate the ECSL and break the debug probe connection. However, peripheral registers are not protected. So, yes, if you halted the device in an unsecure region to avoid JTAG disconnect, you could either modify the unsecure memory or directly read/write to the peripheral registers with the debugger.

  • 0 in reply to Hareesh Janakiraman
    TI__Expert 4405 points

    Hi Hareesh,

    Thanks for your reply! Since customer have network security requirements, customers need to confirm whether there is a possibility that the registers are modified when using CSM. What the customer want to know is: CSM can block FLASH and RAM, whether it can also block registers at the same time.

    According to your reply, the peripheral registers are not protected and can still be accessed and changed through the JTAG port.

    Now the question is as follows:

    1) Are there any risks of being modified except for the peripheral registers? Such as CPU register, when the pointer points to the secured area, access will be prohibited; if it points to the non-secured area, will it not be prohibited from accessing?

    2) Is the difference between CSM and DCSM only the number of security zones? 

    Could you please help answer them? Many thanks!

    Best Regards,

    Julia

  • 0 in reply to Julia Li
    TI__Guru* 95315 points
    Julia Li said:
    1) Are there any risks of being modified except for the peripheral registers? Such as CPU register, when the pointer points to the secured area, access will be prohibited; if it points to the non-secured area, will it not be prohibited from accessing?

    As mentioned before, only (unsecure) peripheral registers may be accessed. Secure resources cannot be accessed/modified.

    Julia Li said:
    2) Is the difference between CSM and DCSM only the number of security zones?

    No, there are a few more differences. The passwords are now stored in the OTP, not flash. Therefore, the password location moves to a different location every time the password needs to be changed. The current password location is tracked by the link pointer. 

  • 0 in reply to Hareesh Janakiraman
    TI__Expert 4405 points

    Hi Hareesh,

    Thank you for your reply! Now customer still want to confirm the following questions:

    1. In the datasheet of F28035, it is mentioned that the flash register and CLA register are protected, as shown in the figure below. However, the same description was not found in the "Peripheral Registers Memory Map" of the F280049 datasheet, so please help to confirm which registers of the 280049 are protected by DCSM?

    2. For mass production in the factory, do we have tools and guidance book for DCSM/CSM programming? I know Uniflash can do this, but customer think it's too time-consuming to use Uniflash in mass production.

    Could you please help answer them? Many thanks!

    Best Regards,

    Julia

  • +1 in reply to Julia Li
    TI__Guru* 95315 points

    EALLOW protection is completely different from DCSM protection. DCSM protects unauthorized copying of the flash contents, which is protected by a password. EALLOW protects registers/bits from being modified by rogue code or unintentionally. There is no passwords involved with EALLOW. These are two completely different mechanisms. Also note that the flash technology used in F280049 is very different from F8035. Hence flash control registers are also different.

    #2: The TRM material is all we have. 

  • +1 in reply to Hareesh Janakiraman
    TI__Guru* 95315 points

    SPNA148 has some information that could be of help.