topic Re: Access to peripherals in UserMode when K82 MPU is enabled in Kinetis Microcontrollers

Access to peripherals in UserMode when K82 MPU is enabled

EugeneHiihtaja — Mon, 18 Jun 2018 16:27:44 GMT

Hi !

It is not so clear from documentation if K82 MPU can be configured for access to simple peripherals (LPUART0 )

in UserMode. All trials to configure LPUART address space in MPU for read/write space dosn't have any effect and simple read of DATA register cause BusFault.

Not all ARM can grant access for this area in UserMode.

But what about K82 ?

Does it possible to configure K82 MPU if in UserMode to have access to LPUART0 and i2C address space ?

Regards,

Eugene

Re: Access to peripherals in UserMode when K82 MPU is enabled

xiangjun_rong — Wed, 20 Jun 2018 09:38:31 GMT

Hi, Eugene,

I think the MPU module is used to protect memory rather than the peripheral as the name MPU implies "memory protection unit".

If you access the peripheral, you can set the AIPSx_PACRn and AIPSx_MPRA register to protect the peripheral.

The LPUART0 module locates at slot 68 of AIPS1 as the Table 5-3. Peripheral bridge 1 slot assignments (continued) which I display as the screenshot.

You can write the AIPS1_PACR68 to set the access right for the LPUART0. You can set the AIPS1_MPRA to configure the different master access right.

Hope it can help you

Xiangjun Rong

Re: Access to peripherals in UserMode when K82 MPU is enabled

EugeneHiihtaja — Wed, 20 Jun 2018 12:51:31 GMT

Hi Xiangjun Rong !

Thank you ! It is really work like this. It have sense to add AIPS table to each TCB of FreeRTOS for get more secure execution environment.

I have few small questions about K82 after that.

1. So it is dosn't have sense to protect by MPU areas after 0x40000000 where peripherals starts ?

Core always have access to this area and only AIPS0/AIPS1 blocks can be used for protect peripheral memory mapped area ?

2. Private Peripherals at address >= 0xE00000000 is always accessible by core in privileged mode and MPU settings dosn't have any effect as well.

By the way , do you have any application note where all peripherals what have effect to security is explained for K82 ?

What should be hardened for get from K82 as max protection as possible ?

Regards,

Eugene