Shadow stack experiments and test code for ARM64 Guarded Control Stack (GCS). For exploring, understanding, and validating GCS mechanisms

Note: Functions in this file are marked static inline intentionally. This was done in order to avoid surprises during disassembly or test instrumentation and keep stack as minimal as possible, reducing cognitive overhead when inspecting the control flow and understanding GCS behavior.

This is test code, not production logic, so predictability is prefered. Additionally disabling ASLR echo 0 > /proc/sys/kernel/randomize_va_space during inspection ensures memory addresses remain consistent across different code revisions, which is super useful to avoid distractions during analysis.

TODO: Give a TL;DR of what the test covers

I usually have it running with an SSH server and the linux-tools dir from the kernel sources copied to the root's home dir so simply:

rsync -rvz -e 'ssh -p 2222' --progress gcs-simple.c [email protected]:/root/linux-tools/testing/selftests/arm64/gcs/gcs-simple.c

Add target to Makefile inside the simulator if you don't have setup a faster choor build env.

$(OUTPUT)/gcs-simple: gcs-simple.c
	$(CC) -g -fno-asynchronous-unwind-tables -fno-ident -Os -nostdlib \
		-static -include ../../../../include/nolibc/nolibc.h \
		-I../../../../../usr/include \
		-std=gnu99 -I../.. -g \
		-ffreestanding -Wall $^ -o $@ -lgcc

cd /root/linux-tools/testing/selftests/arm64/gcs
make CFLAGS="-I../../../selftests -I../../../../../linux-tools/include" $PWD/gcs-simples