Assuming that an exploit with a stack buffer overflow will very likely overwrite that canary, it can be detected by the by the running program. Similar to the canaries used in coal mines, a stack canary is a variable with a special value placed at the end of the stack memory. The MCUXpresso IDE V11 includes the ‘Image Info’ view which calculates the stack space needed:

And both methods are used at context switch time only, so stack overflow detection might not be detected for a while. The second method includes the first plus places a pattern at the end of the stack and verifies it if it has been touched.

In this article I describe an approach with the GNU gcc in a bare-metal (no RTOS) environment, because FreeRTOS already includes an option to check for a stack overflow at runtime: the check is performed at task context switch, see “ FreeRTOS – stacks and stack overflow” for more details.įreeRTOS has two methods: one is just comparing the current task stack pointer with a known stack limit value (if it is outside the stack range). This article uses the NXP MCUXpresso IDE V11 which uses GNU tools. The last option is what can be turned on in FreeRTOS. Place sentinel values at the end of the stack space which are periodically checked.Using hardware watch points to detect the overwrite.Using MPU (Hardware Memory Protection) to detect and protect the overflow.Making a good analysis how much stack is needed.

There are different ways to deal with this:

How to change the image on canary mail