x86/irq/64: Remove stack overflow debug code

All stack types on x86 64-bit have guard pages now.

So there is no point in executing probabilistic overflow checks as the
guard pages are a accurate and reliable overflow prevention.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190414160146.466354762@linutronix.de

arch/x86/Kconfig

@@ -14,6 +14,7 @@ config X86_32
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select CLKSRC_I8253
 	select CLONE_BACKWARDS
+	select HAVE_DEBUG_STACKOVERFLOW
 	select MODULES_USE_ELF_REL
 	select OLD_SIGACTION
 
@@ -138,7 +139,6 @@ config X86
 	select HAVE_COPY_THREAD_TLS
 	select HAVE_C_RECORDMCOUNT
 	select HAVE_DEBUG_KMEMLEAK
-	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS

arch/x86/kernel/irq_64.c

@@ -26,64 +26,8 @@
 DEFINE_PER_CPU_PAGE_ALIGNED(struct irq_stack, irq_stack_backing_store) __visible;
 DECLARE_INIT_PER_CPU(irq_stack_backing_store);
 
-int sysctl_panic_on_stackoverflow;
-
-/*
- * Probabilistic stack overflow check:
- *
- * Regular device interrupts can enter on the following stacks:
- *
- * - User stack
- *
- * - Kernel task stack
- *
- * - Interrupt stack if a device driver reenables interrupts
- *   which should only happen in really old drivers.
- *
- * - Debug IST stack
- *
- * All other contexts are invalid.
- */
-static inline void stack_overflow_check(struct pt_regs *regs)
-{
-#ifdef CONFIG_DEBUG_STACKOVERFLOW
-#define STACK_MARGIN	128
-	u64 irq_stack_top, irq_stack_bottom, estack_top, estack_bottom;
-	u64 curbase = (u64)task_stack_page(current);
-	struct cea_exception_stacks *estacks;
-
-	if (user_mode(regs))
-		return;
-
-	if (regs->sp >= curbase + sizeof(struct pt_regs) + STACK_MARGIN &&
-	    regs->sp <= curbase + THREAD_SIZE)
-		return;
-
-	irq_stack_top = (u64)__this_cpu_read(hardirq_stack_ptr);
-	irq_stack_bottom = irq_stack_top - IRQ_STACK_SIZE + STACK_MARGIN;
-	if (regs->sp >= irq_stack_bottom && regs->sp <= irq_stack_top)
-		return;
-
-	estacks = __this_cpu_read(cea_exception_stacks);
-	estack_top = CEA_ESTACK_TOP(estacks, DB);
-	estack_bottom = CEA_ESTACK_BOT(estacks, DB) + STACK_MARGIN;
-	if (regs->sp >= estack_bottom && regs->sp <= estack_top)
-		return;
-
-	WARN_ONCE(1, "do_IRQ(): %s has overflown the kernel stack (cur:%Lx,sp:%lx, irq stack:%Lx-%Lx, exception stack: %Lx-%Lx, ip:%pF)\n",
-		current->comm, curbase, regs->sp,
-		irq_stack_bottom, irq_stack_top,
-		estack_bottom, estack_top, (void *)regs->ip);
-
-	if (sysctl_panic_on_stackoverflow)
-		panic("low stack detected by irq handler - check messages\n");
-#endif
-}
-
 bool handle_irq(struct irq_desc *desc, struct pt_regs *regs)
 {
-	stack_overflow_check(regs);
-
 	if (IS_ERR_OR_NULL(desc))
 		return false;