arch: arm64: Refactor the stack relevant macros

Refactor the stack relevant macros to prepare to introduce the stack
guard. Also add comments about the changes related to stack layout.

Signed-off-by: Jaxson Han <jaxson.han@arm.com>

arch/arm64/core/reset.S

@@ -7,6 +7,7 @@
 #include <zephyr/toolchain.h>
 #include <zephyr/linker/sections.h>
 #include <zephyr/arch/cpu.h>
+#include <offsets.h>
 #include "boot.h"
 #include "macro_priv.inc"
 
@@ -149,7 +150,7 @@ resetwait:
 primary_core:
 #endif
 	/* load primary stack and entry point */
-	ldr	x24, =(z_interrupt_stacks + CONFIG_ISR_STACK_SIZE)
+	ldr	x24, =(z_interrupt_stacks + __z_interrupt_stack_SIZEOF)
 	ldr	x25, =z_arm64_prep_c
 2:
 	/* Prepare for calling C code */

arch/arm64/core/thread.c

@@ -28,19 +28,35 @@
  *   normal execution. When at exception is taken or a syscall is called the
  *   stack pointer switches to SP_EL1 and the execution starts using the
  *   privileged portion of the user stack without touching SP_EL0. This portion
- *   is marked as not user accessible in the MMU.
+ *   is marked as not user accessible in the MMU/MPU.
+ *
+ * - a stack guard region will be added bellow the kernel stack when
+ *   ARM64_STACK_PROTECTION is enabled. In this case, SP_EL0 will always point
+ *   to the safe exception stack in the kernel space. For the kernel thread,
+ *   SP_EL0 will not change always pointing to safe exception stack. For the
+ *   userspace thread, SP_EL0 will switch from the user stack to the safe
+ *   exception stack when entering the EL1 mode, and restore to the user stack
+ *   when backing to userspace (EL0).
  *
  *   Kernel threads:
  *
+ * High memory addresses
+ *
  *    +---------------+ <- stack_ptr
  *  E |     ESF       |
  *  L |<<<<<<<<<<<<<<<| <- SP_EL1
  *  1 |               |
- *    +---------------+
+ *    +---------------+ <- stack limit
-
+ *    |  Stack guard  | } Z_ARM64_STACK_GUARD_SIZE (protected by MMU/MPU)
+ *    +---------------+ <- stack_obj
+ *
+ * Low Memory addresses
+ *
  *
  *   User threads:
  *
+ * High memory addresses
+ *
  *    +---------------+ <- stack_ptr
  *  E |               |
  *  L |<<<<<<<<<<<<<<<| <- SP_EL0
@@ -49,7 +65,11 @@
  *  E |     ESF       |               |  Privileged portion of the stack
  *  L +>>>>>>>>>>>>>>>+ <- SP_EL1     |_ used during exceptions and syscalls
  *  1 |               |               |  of size ARCH_THREAD_STACK_RESERVED
- *    +---------------+ <- stack_obj..|
+ *    +---------------+ <- stack limit|
+ *    |  Stack guard  | } Z_ARM64_STACK_GUARD_SIZE (protected by MMU/MPU)
+ *    +---------------+ <- stack_obj
+ *
+ * Low Memory addresses
  *
  *  When a kernel thread switches to user mode the SP_EL0 and SP_EL1
  *  values are reset accordingly in arch_user_mode_enter().

include/zephyr/arch/arm64/thread_stack.h

@@ -7,11 +7,11 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARM64_THREAD_STACK_H_
 #define ZEPHYR_INCLUDE_ARCH_ARM64_THREAD_STACK_H_
 
+#include <zephyr/arch/arm64/mm.h>
 
 #define ARCH_STACK_PTR_ALIGN			16
 
-#if CONFIG_USERSPACE
+#if defined(CONFIG_USERSPACE) || defined(CONFIG_ARM64_STACK_PROTECTION)
-#include <zephyr/arch/arm64/mm.h>
 #define Z_ARM64_STACK_BASE_ALIGN		MEM_DOMAIN_ALIGN_AND_SIZE
 #define Z_ARM64_STACK_SIZE_ALIGN		MEM_DOMAIN_ALIGN_AND_SIZE
 #else
@@ -19,6 +19,14 @@
 #define Z_ARM64_STACK_SIZE_ALIGN		ARCH_STACK_PTR_ALIGN
 #endif
 
+#if defined(CONFIG_ARM64_STACK_PROTECTION)
+#define Z_ARM64_STACK_GUARD_SIZE		MEM_DOMAIN_ALIGN_AND_SIZE
+#define Z_ARM64_K_STACK_BASE_ALIGN		MEM_DOMAIN_ALIGN_AND_SIZE
+#else
+#define Z_ARM64_STACK_GUARD_SIZE		0
+#define Z_ARM64_K_STACK_BASE_ALIGN		ARCH_STACK_PTR_ALIGN
+#endif
+
 /*
  * [ see also comments in arch/arm64/core/thread.c ]
  *
@@ -36,6 +44,8 @@
  * |                   |
  * +-------------------+ <- thread.stack_info.start
  * | Privileged stack  | } K_(THREAD|KERNEL)_STACK_RESERVED
+ * +-------------------+ <- thread stack limit (update on every context switch)
+ * |    Stack guard    | } Z_ARM64_STACK_GUARD_SIZE (protected by MMU/MPU)
  * +-------------------+ <- thread.stack_obj
  *
  * Low Memory addresses
@@ -45,11 +55,12 @@
 #define ARCH_THREAD_STACK_OBJ_ALIGN(size)	Z_ARM64_STACK_BASE_ALIGN
 #define ARCH_THREAD_STACK_SIZE_ADJUST(size)	\
 	ROUND_UP((size), Z_ARM64_STACK_SIZE_ALIGN)
-#define ARCH_THREAD_STACK_RESERVED		CONFIG_PRIVILEGED_STACK_SIZE
+#define ARCH_THREAD_STACK_RESERVED		CONFIG_PRIVILEGED_STACK_SIZE + \
+	Z_ARM64_STACK_GUARD_SIZE
 
 /* kernel stack */
-#define ARCH_KERNEL_STACK_RESERVED		0
+#define ARCH_KERNEL_STACK_RESERVED		Z_ARM64_STACK_GUARD_SIZE
-#define ARCH_KERNEL_STACK_OBJ_ALIGN		ARCH_STACK_PTR_ALIGN
+#define ARCH_KERNEL_STACK_OBJ_ALIGN		Z_ARM64_K_STACK_BASE_ALIGN
 
 #ifndef _ASMLANGUAGE