[6/6] arrange for a guard page on cpu 0's IRQ stack (was: Re: [-mm patch] i386: enable 4k stacks by default)

[William Lee Irwin III <wli@holomorphy.com>]

On Mon, Apr 30, 2007 at 10:38:19AM -0700, William Lee Irwin III wrote:
> Here's what I did for i386 for someone concerned about blowing the stack.

vmap() cpu 0's IRQ stack to ensure a guard page for it.

Signed-off-by: William Irwin <wli@holomorphy.com>


Index: stack-paranoia/arch/i386/kernel/irq.c
===================================================================
--- stack-paranoia.orig/arch/i386/kernel/irq.c	2007-04-30 10:36:14.553987258 -0700
+++ stack-paranoia/arch/i386/kernel/irq.c	2007-04-30 10:37:09.909141769 -0700
@@ -17,6 +17,7 @@
 #include <linux/notifier.h>
 #include <linux/cpu.h>
 #include <linux/delay.h>
+#include <linux/mm.h>
 #include <linux/bootmem.h>
 
 #include <asm/apic.h>
@@ -156,6 +157,41 @@
 static DEFINE_PER_CPU(char *, hardirq_stack);
 
 #ifdef CONFIG_VMALLOC_STACK
+static void * __init irq_remap_stack(void *stack)
+{
+	int i;
+	struct page *pages[THREAD_SIZE/PAGE_SIZE];
+
+	for (i = 0; i < ARRAY_SIZE(pages); ++i)
+		pages[i] =  virt_to_page(stack + PAGE_SIZE*i);
+	return vmap(pages, THREAD_SIZE/PAGE_SIZE, VM_IOREMAP, PAGE_KERNEL);
+}
+
+static int __init irq_guard_cpu0(void)
+{
+	unsigned long flags;
+	void *tmp;
+
+	tmp = irq_remap_stack(per_cpu(softirq_stack, 0));
+	if (!tmp)
+		return -ENOMEM;
+	else {
+		local_irq_save(flags);
+		per_cpu(softirq_stack, 0) = tmp;
+		local_irq_restore(flags);
+	}
+	tmp = irq_remap_stack(per_cpu(hardirq_stack, 0));
+	if (!tmp)
+		return -ENOMEM;
+	else {
+		local_irq_save(flags);
+		per_cpu(hardirq_stack, 0) = tmp;
+		local_irq_restore(flags);
+	}
+	return 0;
+}
+core_initcall(irq_guard_cpu0);
+
 static void * __init __alloc_irqstack(int cpu)
 {
 	int i;