2381341_en-US

[#1]

SEC_CONFIG fuse on iMX8 Mini

Hi,

I'm trying to enable secure boot on a custom hardware platform based on iMX8 Mini.

By following the available documentation, I was able to create a boot image with correct signatures, I'm sure about that because the hab_status command did not show any hab event and also the image verifier tool did not show any error.

To close the device, I programmed the SRK_HASH fuses and the SEC_CONFIG fuses, but after this step my board does not start anymore and does not show anything on serial console.

I'm quite sure that the SRK_HASH has been programmed properly, but I have doubts on SEC_CONFIG: to enable secure boot I should have used the below command:

fuse prog 1 3 0x02000000

that sets bit 25.

However, before doing the modification, I read the content of SEC_CONFIG and I saw the below value:

fuse read 1 3

0x8000000

So, since I saw bit 27 set to 1, I had the great idea to use the below command:

fuse prog 1 3 0x0A000000

To preserve bit 27 and set bit 25.

Question:

Is it possible that the above command put SEC_CONFIG to an invalid value so that the ROM bootloader does not even start the SPL?

If yes, is there any way to restore the board?

Best Regards

Re: SEC_CONFIG fuse on iMX8 Mini

Hi,

many thanks for your answer, this is coherent with the current behaviour.

Only a last question:

Since I did not program any lock bit, do you think that using an hardware debugger would it be possible to restore the board?

Best Regards

Re: SEC_CONFIG fuse on iMX8 Mini

If the chip became bricked after the reserved bits were written, then it is impossible to restore the chip, because the fuse operation is a one-time and irreversible process.

Re: SEC_CONFIG fuse on iMX8 Mini

Bit 27 is a reserved bit and cannot be programmed by the customer. Rather than whether this command(fuse prog 1 3 0x0A000000) will invalidate sec_config, it is more likely that the behavior of the entire chip will become unpredictable.

Re: SEC_CONFIG fuse on iMX8 Mini

Hello,

Unfortunately, no, not by clearing fuses, eFuses are one-time programmable. Once sec_config is blown, you cannot “unblow” it