scheduler: Fix page table switch for scheduler

The userspace process may map pages where the kernel has allocated data and cause a crash.

This patch fixes this issue by having a separate IRQ handler which sets the kernel page table at the start of SchedulerInterruptHandler() and restores it in SchedulerHandlerStub() function.

include/cpu.hpp

@@ -641,6 +641,38 @@ namespace CPU
 			uint64_t ss;   /* Stack Segment */
 		};
 
+		struct SchedulerFrame
+		{
+			uint64_t ppt; /* Process Page Table */
+			uint64_t opt; /* Original Page Table */
+
+			uint64_t r15; /* General purpose */
+			uint64_t r14; /* General purpose */
+			uint64_t r13; /* General purpose */
+			uint64_t r12; /* General purpose */
+			uint64_t r11; /* General purpose */
+			uint64_t r10; /* General purpose */
+			uint64_t r9;  /* General purpose */
+			uint64_t r8;  /* General purpose */
+
+			uint64_t rbp; /* Base Pointer (meant for stack frames) */
+			uint64_t rdi; /* Destination index for string operations */
+			uint64_t rsi; /* Source index for string operations */
+			uint64_t rdx; /* Data (commonly extends the A register) */
+			uint64_t rcx; /* Counter */
+			uint64_t rbx; /* Base */
+			uint64_t rax; /* Accumulator */
+
+			uint64_t InterruptNumber; /* Interrupt Number */
+			uint64_t ErrorCode;		  /* Error code */
+
+			uint64_t rip;  /* Instruction Pointer */
+			uint64_t cs;   /* Code Segment */
+			RFLAGS rflags; /* Register Flags */
+			uint64_t rsp;  /* Stack Pointer */
+			uint64_t ss;   /* Stack Segment */
+		};
+
 		struct ExceptionFrame
 		{
 			uint64_t cr0; /* Control Register 0 (system control) */
@@ -1026,6 +1058,7 @@ namespace CPU
 	 * @note This is for x86_64
 	 */
 	typedef x64::TrapFrame TrapFrame;
+	typedef x64::SchedulerFrame SchedulerFrame;
 	typedef x64::ExceptionFrame ExceptionFrame;
 #elif defined(a32)
 	/**
@@ -1034,6 +1067,7 @@ namespace CPU
 	 * @note This is for x86_32
 	 */
 	typedef x32::TrapFrame TrapFrame;
+	typedef x32::SchedulerFrame SchedulerFrame;
 	typedef x32::ExceptionFrame ExceptionFrame;
 #elif defined(aa64)
 	/**
@@ -1042,6 +1076,7 @@ namespace CPU
 	 * @note This is for aarch64
 	 */
 	typedef aarch64::TrapFrame TrapFrame;
+	typedef aarch64::SchedulerFrame SchedulerFrame;
 	typedef aarch64::TrapFrame ExceptionFrame;
 #endif
 }

include/ints.hpp

@@ -78,6 +78,7 @@ namespace Interrupts
 
 	public:
 		virtual void OnInterruptReceived(CPU::TrapFrame *Frame);
+		virtual void OnInterruptReceived(CPU::SchedulerFrame *Frame);
 	};
 }
 

include/scheduler.hpp

@@ -142,8 +142,8 @@ namespace Tasking::Scheduler
 		void WakeUpThreads();
 		void CleanupTerminated();
 
-		void Schedule(CPU::TrapFrame *Frame);
-		void OnInterruptReceived(CPU::TrapFrame *Frame) final;
+		void Schedule(CPU::SchedulerFrame *Frame);
+		void OnInterruptReceived(CPU::SchedulerFrame *Frame) final;
 
 		Custom(Task *ctx);
 		virtual ~Custom();

include/signal.hpp

@@ -312,11 +312,11 @@ namespace Tasking
 		{
 #ifdef a64
 			CPU::x64::FXState fx;
-			CPU::x64::TrapFrame tf;
+			CPU::x64::SchedulerFrame tf;
 			uintptr_t GSBase, FSBase, ShadowGSBase;
 #else
 			CPU::x32::FXState fx;
-			CPU::x32::TrapFrame tf;
+			CPU::x32::SchedulerFrame tf;
 			uintptr_t GSBase, FSBase;
 #endif
 			sigset_t SignalMask;
@@ -422,7 +422,7 @@ namespace Tasking
 		int AddSignal(Signals sig, union sigval val = {0}, pid_t tid = -1);
 		int RemoveSignal(Signals sig);
 
-		bool HandleSignal(CPU::TrapFrame *tf, void *thread);
+		bool HandleSignal(CPU::SchedulerFrame *tf, void *thread);
 		void RestoreHandleSignal(SyscallsFrame *tf, void *thread);
 
 		int SetAction(Signals sig, const SignalAction *act);

include/task.hpp

@@ -356,10 +356,10 @@ namespace Tasking
 
 		/* CPU state */
 #if defined(a64)
-		CPU::x64::TrapFrame Registers{};
+		CPU::x64::SchedulerFrame Registers{};
 		uintptr_t ShadowGSBase, GSBase, FSBase;
 #elif defined(a32)
-		CPU::x32::TrapFrame Registers{};
+		CPU::x32::SchedulerFrame Registers{};
 		uintptr_t ShadowGSBase, GSBase, FSBase;
 #elif defined(aa64)
 		uintptr_t Registers; // TODO