Index: kernel/arch/amd64/src/asm.S
===================================================================
--- kernel/arch/amd64/src/asm.S	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/amd64/src/asm.S	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -362,5 +362,13 @@
 	 */
 	call syscall_handler
-	
+
+	/*
+	 * Test if the saved return address is canonical and not-kernel.
+	 * We do this by looking at the 16 most significant bits
+	 * of the saved return address (two bytes at offset 6).
+	 */
+	testw $0xffff, ISTATE_OFFSET_RIP+6(%rsp)
+	jnz bad_rip 
+
 	cli
 	
@@ -388,4 +396,14 @@
 	sysretq
 
+bad_rip:
+	movq %rsp, %rdi
+	movabs $bad_rip_msg, %rsi
+	xorb %al, %al
+	callq fault_from_uspace
+	/* not reached */
+	
+bad_rip_msg:
+	.asciz "Invalid instruction pointer."
+
 /** Print Unicode character to EGA display.
  *
Index: kernel/arch/amd64/src/boot/multiboot.S
===================================================================
--- kernel/arch/amd64/src/boot/multiboot.S	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/amd64/src/boot/multiboot.S	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -76,4 +76,5 @@
 
 multiboot_image_start:
+	cli
 	cld
 	
@@ -81,6 +82,10 @@
 	movl $START_STACK, %esp
 	
-	/* Initialize Global Descriptor Table register */
+	/*
+	 * Initialize Global Descriptor Table and
+	 * Interrupt Descriptor Table registers
+	 */
 	lgdtl bootstrap_gdtr
+	lidtl bootstrap_idtr
 	
 	/* Kernel data + stack */
@@ -645,4 +650,9 @@
 .section K_DATA_START, "aw", @progbits
 
+.global bootstrap_idtr
+bootstrap_idtr:
+	.word 0
+	.long 0
+
 .global bootstrap_gdtr
 bootstrap_gdtr:
Index: kernel/arch/amd64/src/boot/multiboot2.S
===================================================================
--- kernel/arch/amd64/src/boot/multiboot2.S	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/amd64/src/boot/multiboot2.S	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -116,4 +116,5 @@
 
 multiboot2_image_start:
+	cli
 	cld
 	
@@ -121,6 +122,10 @@
 	movl $START_STACK, %esp
 	
-	/* Initialize Global Descriptor Table register */
+	/*
+	 * Initialize Global Descriptor Table and
+	 * Interrupt Descriptor Table registers
+	 */
 	lgdtl bootstrap_gdtr
+	lidtl bootstrap_idtr
 	
 	/* Kernel data + stack */
Index: kernel/arch/amd64/src/boot/vesa_ret.inc
===================================================================
--- kernel/arch/amd64/src/boot/vesa_ret.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/amd64/src/boot/vesa_ret.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -1,4 +1,5 @@
 .code32
 vesa_init_protected:
+	cli
 	cld
 	
Index: kernel/arch/ia32/src/boot/multiboot.S
===================================================================
--- kernel/arch/ia32/src/boot/multiboot.S	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia32/src/boot/multiboot.S	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -73,4 +73,5 @@
 
 multiboot_image_start:
+	cli
 	cld
 	
@@ -78,6 +79,10 @@
 	movl $START_STACK, %esp
 	
-	/* Initialize Global Descriptor Table register */
+	/*
+	 * Initialize Global Descriptor Table and
+	 * Interrupt Descriptor Table registers
+	 */
 	lgdtl bootstrap_gdtr
+	lidtl bootstrap_idtr
 	
 	/* Kernel data + stack */
@@ -701,4 +706,9 @@
 page_directory:
 	.space 4096, 0
+
+.global bootstrap_idtr
+bootstrap_idtr:
+	.word 0
+	.long 0
 
 .global bootstrap_gdtr
Index: kernel/arch/ia32/src/boot/multiboot2.S
===================================================================
--- kernel/arch/ia32/src/boot/multiboot2.S	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia32/src/boot/multiboot2.S	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -114,4 +114,5 @@
 
 multiboot2_image_start:
+	cli
 	cld
 	
@@ -119,6 +120,10 @@
 	movl $START_STACK, %esp
 	
-	/* Initialize Global Descriptor Table register */
+	/*
+	 * Initialize Global Descriptor Table and
+	 * Interrupt Descriptor Table registers
+	 */
 	lgdtl bootstrap_gdtr
+	lidtl bootstrap_idtr
 	
 	/* Kernel data + stack */
Index: kernel/arch/ia32/src/boot/vesa_prot.inc
===================================================================
--- kernel/arch/ia32/src/boot/vesa_prot.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia32/src/boot/vesa_prot.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -88,4 +88,11 @@
 		/* Returned back to protected mode */
 		
+		/*
+		 * Initialize Global Descriptor Table and
+		 * Interrupt Descriptor Table registers
+		 */
+		lgdtl bootstrap_gdtr
+		lidtl bootstrap_idtr
+		
 		movzx %ax, %ecx
 		mov %ecx, KA2PA(bfb_scanline)
Index: kernel/arch/ia32/src/boot/vesa_real.inc
===================================================================
--- kernel/arch/ia32/src/boot/vesa_real.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia32/src/boot/vesa_real.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -30,5 +30,10 @@
 .code32
 vesa_init:
+	lidtl vesa_idtr
 	jmp $GDT_SELECTOR(VESA_INIT_DES), $vesa_init_real - vesa_init
+
+vesa_idtr:
+	.word 0x3ff
+	.long 0
 
 .code16
Index: kernel/arch/ia32/src/boot/vesa_ret.inc
===================================================================
--- kernel/arch/ia32/src/boot/vesa_ret.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia32/src/boot/vesa_ret.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -1,4 +1,5 @@
 .code32
 vesa_init_protected:
+	cli
 	cld
 	
Index: kernel/arch/ia64/Makefile.inc
===================================================================
--- kernel/arch/ia64/Makefile.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/ia64/Makefile.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -30,5 +30,15 @@
 BFD_ARCH = ia64-elf64
 
-CMN1 = -mconstant-gp -fno-unwind-tables -mfixed-range=f32-f127
+#
+# FIXME:
+#
+# The -fno-selective-scheduling and -fno-selective-scheduling2 options
+# should be removed as soon as a bug in GCC concerning unchecked
+# speculative loads is fixed.
+#
+# See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53975 for reference.
+#
+
+CMN1 = -mconstant-gp -fno-unwind-tables -mfixed-range=f32-f127 -fno-selective-scheduling -fno-selective-scheduling2
 GCC_CFLAGS += $(CMN1)
 ICC_CFLAGS += $(CMN1)
Index: kernel/arch/mips32/Makefile.inc
===================================================================
--- kernel/arch/mips32/Makefile.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/mips32/Makefile.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -29,5 +29,5 @@
 BFD_ARCH = mips
 BFD = binary
-GCC_CFLAGS += -mno-abicalls -G 0 -fno-zero-initialized-in-bss -mips3 -mabi=32
+GCC_CFLAGS += -msoft-float -mno-abicalls -G 0 -fno-zero-initialized-in-bss -mips3 -mabi=32
 
 BITS = 32
@@ -48,5 +48,4 @@
 	BFD_NAME = elf32-tradlittlemips
 	ENDIANESS = LE
-	GCC_CFLAGS += -mhard-float
 endif
 
Index: kernel/arch/mips64/Makefile.inc
===================================================================
--- kernel/arch/mips64/Makefile.inc	(revision e0d5bc58083a7cd9a8327d934709edaa0afdc535)
+++ kernel/arch/mips64/Makefile.inc	(revision a8ca607b522246c35732730a751d457dcaf036f0)
@@ -29,5 +29,5 @@
 BFD_ARCH = mips:4000
 BFD = binary
-GCC_CFLAGS += -mno-abicalls -G 0 -fno-zero-initialized-in-bss -mips3 -mabi=64
+GCC_CFLAGS += -msoft-float -mno-abicalls -G 0 -fno-zero-initialized-in-bss -mips3 -mabi=64
 AFLAGS = -64
 
@@ -40,5 +40,4 @@
 	BFD_NAME = elf64-tradlittlemips
 	ENDIANESS = LE
-	GCC_CFLAGS += -mhard-float
 endif