STM32 Trusted Package Creator ignoring Security Counter

[Christian Keydel]

Using STM32TRUSTEE-SM framework, the non-secure application is built by the project.py script which in turn calls

STM32TrustedPackageCreator_CLI.exe -pb SM_Code_Image_bin.xml

to generate the application .bin file in MCUboot format.

The xml file has

	<Param>
		<Name>Security Counter</Name>
		<Value>auto</Value>
		<Type>Data</Type>
		<Command>-s</Command>
		<Hidden>1</Hidden>
		<Default>auto</Default>
	</Param>

It is my understanding that with this setting, an incrementing counter should be placed in the image header's ih_ver.iv_build_num field. But this field stays 0 no matter what I put under <Value>, auto or direct number.

There is a command "-s" which according to the documentation would be passed on to the imgtool executable, which, however, is described as this

and therefore would have nothing to do with any counter.

Could anybody shed some light on it, please? I am using the latest version 2.20.0 of CubeProgrammer/TPC.

[Christian Keydel · Accepted solution]

Answering my own question, I looked into the imgtool further and here is what I found:

The "Slot" reference for the -s parameter in the documentation is wrong. "-s auto" uses a 32-bit value in the format: 0xAABBCCCC with AA=major, BB=minor and CCCC=revision and these values come straight from the -v parameters which comes from "Version" in the XML file.

These values therefore go into two places in the generated .bin file: 1. The header (version info) and 2. Into the TLV as the IMAGE_TLV_SEC_CNT entry in the protected area (security counter.

The ih_ver.iv_build_num field in the header has nothing to do with it but it can be set to any 32-bit value (purely informational) by using the major.minor.revision+build format for "Version" in the XML, e.g.

1.0.3+123456