AM6442: Security: keywriter not validated with eMMC boot source

Andy Green

Part Number: AM6442

Tool/software:

Hi -

In addition to needing to make devices follow Secure Boot at the factory, we want to blow fuses in the field for anti-rollback epoch management purposes.

As such, in both cases, we plan to be booting from SD or eMMC, and then later want to write fuses.

The TI documentation does not claim that this has been "validated", instead it claims paths like JTAG or serial (in fact, serial boot is not usable on am6442 due to an errata) are 'validated'.

What is the situation with burning fuses in the field after eMMC boot, eg, while Linux is running: is it reliable? If not, what are the constraints?

Thanks,

Andy

over 1 year ago

0 Prashant Shivhare over 1 year ago

TI__Guru* 84781 points

Hello,

The Keywriter is a SBL application & so can be booted over any ROM supported boot media. From the runtime functionality point of view, the keywriter does not involve usage of any media & so is agnostic of them.

The OTP updates in the field for anti-rollback, which is supported by the following TISCI messages, are also agnostic of any media.

https://software-dl.ti.com/tisci/esd/latest/2_tisci_msgs/security/otp_revision.html

Regards,

Prashant

0 Andy Green over 1 year ago in reply to Prashant Shivhare

Prodigy 70 points

Thanks... should I understand from this that it's OK to just treat keywriter as a way to generate certificates, which can be passed into SCI from Linux using the message you point to?

Keywriter (whose docs is the source of the 'validation' info) seems to also want to be booted into, but if that is optional, and can be ignored, it's all to the good.

If it's true (it's certainly preferable), how does the management of the 1.8V fuse power fit into it?

Thanks,

-Andy

+1 Prashant Shivhare over 1 year ago in reply to Andy Green

TI__Guru* 84781 points

Hello,

The Keywriter for it's functionality requires a special SYSFW which comes with the Keywriter package itself. This SYSFW is different from the usual SYSFW delivered with the SDKs and are not interchangeable. So, the Keywriting procedure using TISCI_MSG_KEY_WRITER cannot be done from any software other than keywriter itself.

As for the OTP Revision messages, they can be requested from the SDKs. It is expected that the 1.8V is supplied one way or another before the request to SYSFW. The MCU+ SDK has an example for the SWREV

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/10_00_00_20/exports/docs/api_guide_am64x/EXAMPLES_RUNTIME_SWREV.html

Regards,

Prashant

0 Andy Green over 1 year ago in reply to Prashant Shivhare

Prodigy 70 points

I see, thanks for the explanation.

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AM6442: Security: keywriter not validated with eMMC boot source