The gcc original implementation does not catch my case above where the allocated stack for the application overflows. 💡 The point to make here is: the check is something has overwritten the stack space of the instrumented function (printValue() in this case). Void _stack_chk_fail(void) resore pushed regs Unsigned long _stack_chk_guard = 0xDEADBEEF error callback function, named _stack_chk_failīelow is a very simple implementation of this:.stack guard (32bit) value, ideally with a ‘random’ value, named _stack_chk_guard.If using the Stack Guard functionality of the GNU compiler, I have to provide two things: Possibly that printf() might cause a stack overflow: fstack-protector-all: Like -fstack-protector except that all functions are protected.įor example add that option to the compiler settings like this:īelow is a small function which prints a value. If a guard check fails, an error message is printed and the program exits. The guards are initialized when a function is entered and then checked when the function exits. This includes functions that call alloca, and functions with buffers larger than 8 bytes. This is done by adding a guard variable to functions with vulnerable objects.
STACK SMASHING DETECTED RECURSION CODE
fstack-protector: Emit extra code to check for buffer overflows, such as stack smashing attacks.
The gcc compiler provides a set of options to use canaries (see ). 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.
STACK SMASHING DETECTED RECURSION PLUS
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:
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