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