60 lines
2.2 KiB
ReStructuredText
60 lines
2.2 KiB
ReStructuredText
.. _userspace_protected_memory:
|
|
|
|
Userspace Protected Memory
|
|
##########################
|
|
|
|
Overview
|
|
********
|
|
This sample is an example of running multiple threads assigned
|
|
unique memory domains with protected partitions. The
|
|
application uses memory partitioning with a sample algorithm
|
|
simulating an enigma-like machine, but the implementation of the
|
|
machine has not been validated and should not be used for any
|
|
actual security purposes.
|
|
|
|
Requirements
|
|
************
|
|
|
|
The sample is dependent on the subsystem app_memory, and it will
|
|
not run on boards that do not support the subsystem. The sample
|
|
was tested on the following boards qemu_x86,frdm_k64, and ``96b_carbon/stm32f401xe``.
|
|
|
|
Building and Running
|
|
********************
|
|
|
|
This example will only cover the qemu_x86 board, since the sample
|
|
just prints text to a console.
|
|
|
|
.. zephyr-app-commands::
|
|
:zephyr-app: samples/userspace/shared_mem
|
|
:board: qemu_x86
|
|
:goals: build run
|
|
:compact:
|
|
|
|
After starting, the console will display multiple starting messages
|
|
followed by two series of repeating messages. The repeating messages
|
|
are the input and output of the enigma-like machine. The second
|
|
message is the output of the first message, and the resulting
|
|
output is the first message without spaces. The two messages are
|
|
marked as 1 and 1' respectively.
|
|
|
|
Exit QEMU by pressing :kbd:`CTRL+A` :kbd:`x`.
|
|
|
|
Two definitions can be inserted to change the wheel settings and print
|
|
the state information. To enable the definitions uncomment the last
|
|
two lines in CMakeLists.txt.
|
|
|
|
Functionality
|
|
*************
|
|
The PT thread sends a message followed by the encrypted version of the
|
|
message after sleeping. To send the message the PT thread checks a
|
|
flag, and if it is clear, writes the message to a buffer shared with
|
|
the encrypt thread. After writing the buffer, the flag is set. The
|
|
encrypt thread copies the memory from the common buffer into the
|
|
encrypted thread's private memory when the flag is set and then clears
|
|
the flag. Once the encrypted thread receives the text string, it
|
|
performs a simulation of the enigma machine to produce cypher text(CT).
|
|
The CT is copied to a shared memory partition connecting to the third
|
|
thread. The third thread prints the CT to the console with a banner
|
|
denoting the content as CYPHER TEXT.
|