Handout

kernel/arch/core_ring.h

@@ -0,0 +1,31 @@
+
+#pragma once
+#include "../types.h"
+
+namespace Core {
+/*! \brief Protection Rings
+ */
+namespace Ring {
+
+/*! \brief Switch to Ring 3
+ *
+ * \param stackpointer       usermode stack pointer
+ * \param kickoff            pointer to function in user mode
+ * \param kickoff_parameter  put in register for 1. function parameter
+ */
+[[gnu::noreturn]]
+void switchToUsermode(void *stackpointer, void *kickoff,
+					  void *kickoff_parameter);
+
+/*! \brief Get current protection level
+ *
+ *  \return current ring
+ */
+inline unsigned get() {
+	unsigned cs;
+	asm volatile("mov %%cs, %0\n\t" : "=r"(cs)::"memory");
+	return cs & 0b11;  // last bits define the ring
+}
+
+}  // namespace Ring
+}  // namespace Core