This patch introduces CONFIG_DEBUG_STACK, which vmalloc()'s task and IRQ
stacks in order to establish guard pages. In such a manner any stack
overflow that references pages immediately adjacent to the stack is
immediately trapped with a fault, which precludes silent memory corruption
or difficult-to-decipher failure modes resulting from stack corruption.
It furthermore adds a check to __pa() to catch drivers trying to DMA off
the stack, which more generally flags incorrect attempts to use __pa()
on vmallocspace addresses.
Signed-off-by: William Irwin <[EMAIL PROTECTED]>
Index: stack-paranoia/arch/i386/Kconfig.debug
===================================================================
--- stack-paranoia.orig/arch/i386/Kconfig.debug 2007-04-30 14:43:02.849863948
-0700
+++ stack-paranoia/arch/i386/Kconfig.debug 2007-04-30 14:58:50.483866532
-0700
@@ -35,6 +35,16 @@
This option will slow down process creation somewhat.
+config DEBUG_STACK
+ bool "Debug stack overflows"
+ depends on DEBUG_KERNEL
+ help
+ Allocates the stack physically discontiguously and from high
+ memory. Furthermore an unmapped guard page follows the stack,
+ which results in immediately trapping stack overflows instead
+ of silent corruption. This is not for end-users. It's intended
+ to trigger fatal system errors under various forms of stack abuse.
+
comment "Page alloc debug is incompatible with Software Suspend on i386"
depends on DEBUG_KERNEL && SOFTWARE_SUSPEND
Index: stack-paranoia/arch/i386/kernel/process.c
===================================================================
--- stack-paranoia.orig/arch/i386/kernel/process.c 2007-04-30
14:43:02.857864404 -0700
+++ stack-paranoia/arch/i386/kernel/process.c 2007-04-30 14:56:16.499091440
-0700
@@ -25,6 +25,7 @@
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
+#include <linux/workqueue.h>
#include <linux/user.h>
#include <linux/a.out.h>
#include <linux/interrupt.h>
@@ -322,6 +323,58 @@
show_trace(NULL, regs, ®s->esp);
}
+#ifdef CONFIG_DEBUG_STACK
+struct thread_info *alloc_thread_info(struct task_struct *unused)
+{
+ int i;
+ struct page *pages[THREAD_SIZE/PAGE_SIZE], **tmp = pages;
+ struct vm_struct *area;
+
+ /*
+ * passing VM_IOREMAP for the sake of alignment is why
+ * all this is done by hand.
+ */
+ area = get_vm_area(THREAD_SIZE, VM_IOREMAP);
+ if (!area)
+ return NULL;
+ for (i = 0; i < THREAD_SIZE/PAGE_SIZE; ++i) {
+ pages[i] = alloc_page(GFP_HIGHUSER);
+ if (!pages[i])
+ goto out_free_pages;
+ }
+ /* implicitly transfer page refcounts to the vm_struct */
+ if (map_vm_area(area, PAGE_KERNEL, &tmp))
+ goto out_remove_area;
+ /* it may be worth poisoning, save thread_info proper */
+ return (struct thread_info *)area->addr;
+out_remove_area:
+ remove_vm_area(area);
+out_free_pages:
+ do {
+ __free_page(pages[--i]);
+ } while (i >= 0);
+ return NULL;
+}
+
+static void work_free_thread_info(struct work_struct *work)
+{
+ int i;
+ void *p = work;
+
+ for (i = 0; i < THREAD_SIZE/PAGE_SIZE; ++i)
+ __free_page(vmalloc_to_page(p + PAGE_SIZE*i));
+ vfree(p);
+}
+
+void free_thread_info(struct thread_info *info)
+{
+ struct work_struct *work = (struct work_struct *)info;
+
+ INIT_WORK(work, work_free_thread_info);
+ schedule_work(work);
+}
+#endif
+
/*
* This gets run with %ebx containing the
* function to call, and %edx containing
Index: stack-paranoia/include/asm-i386/module.h
===================================================================
--- stack-paranoia.orig/include/asm-i386/module.h 2007-04-30
14:43:02.905867139 -0700
+++ stack-paranoia/include/asm-i386/module.h 2007-04-30 14:59:27.005947807
-0700
@@ -68,6 +68,13 @@
#define MODULE_STACKSIZE ""
#endif
-#define MODULE_ARCH_VERMAGIC MODULE_PROC_FAMILY MODULE_STACKSIZE
+#ifdef CONFIG_DEBUG_STACK
+#define MODULE_DEBUG_STACK "DEBUG_STACKS "
+#else
+#define MODULE_DEBUG_STACK ""
+#endif
+
+#define MODULE_ARCH_VERMAGIC MODULE_PROC_FAMILY MODULE_STACKSIZE \
+ MODULE_DEBUG_STACK
#endif /* _ASM_I386_MODULE_H */
Index: stack-paranoia/include/asm-i386/thread_info.h
===================================================================
--- stack-paranoia.orig/include/asm-i386/thread_info.h 2007-04-30
14:43:02.913867595 -0700
+++ stack-paranoia/include/asm-i386/thread_info.h 2007-04-30
15:00:59.963245141 -0700
@@ -94,6 +94,11 @@
}
/* thread information allocation */
+#ifdef CONFIG_DEBUG_STACK
+struct task_struct;
+struct thread_info *alloc_thread_info(struct task_struct *);
+void free_thread_info(struct thread_info *);
+#else /* !CONFIG_DEBUG_STACK */
#ifdef CONFIG_DEBUG_STACK_USAGE
#define alloc_thread_info(tsk) kzalloc(THREAD_SIZE, GFP_KERNEL)
#else
@@ -101,6 +106,7 @@
#endif
#define free_thread_info(info) kfree(info)
+#endif /* !CONFIG_DEBUG_STACK */
#else /* !__ASSEMBLY__ */
Index: stack-paranoia/arch/i386/kernel/doublefault.c
===================================================================
--- stack-paranoia.orig/arch/i386/kernel/doublefault.c 2007-04-30
14:43:02.877865543 -0700
+++ stack-paranoia/arch/i386/kernel/doublefault.c 2007-04-30
14:47:16.200301566 -0700
@@ -62,5 +62,5 @@
.ss = __KERNEL_DS,
.ds = __USER_DS,
- .__cr3 = __pa(swapper_pg_dir)
+ .__cr3 = (unsigned long)swapper_pg_dir - PAGE_OFFSET,
};
Index: stack-paranoia/arch/i386/kernel/irq.c
===================================================================
--- stack-paranoia.orig/arch/i386/kernel/irq.c 2007-04-30 14:43:02.869865087
-0700
+++ stack-paranoia/arch/i386/kernel/irq.c 2007-04-30 14:57:02.933737599
-0700
@@ -18,7 +18,7 @@
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/bootmem.h>
-
+#include <linux/mm.h>
#include <asm/apic.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -145,6 +145,60 @@
static DEFINE_PER_CPU(char *, softirq_stack);
static DEFINE_PER_CPU(char *, hardirq_stack);
+#ifdef CONFIG_DEBUG_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;
+ struct page *pages[THREAD_SIZE/PAGE_SIZE], **tmp = pages;
+ struct vm_struct *area;
+
+ if (!cpu)
+ return __alloc_bootmem(THREAD_SIZE, THREAD_SIZE,
+ __pa(MAX_DMA_ADDRESS));
+
+ /* failures here are unrecoverable anyway */
+ area = get_vm_area(THREAD_SIZE, VM_IOREMAP);
+ for (i = 0; i < ARRAY_SIZE(pages); ++i)
+ pages[i] = alloc_page(GFP_HIGHUSER);
+ map_vm_area(area, PAGE_KERNEL, &tmp);
+ return area->addr;
+}
+#else /* !CONFIG_DEBUG_STACK */
static void * __init __alloc_irqstack(int cpu)
{
if (!cpu)
@@ -154,6 +208,7 @@
return (void *)__get_free_pages(GFP_KERNEL,
ilog2(THREAD_SIZE/PAGE_SIZE));
}
+#endif /* !CONFIG_DEBUG_STACK */
static void __init alloc_irqstacks(int cpu)
{
Index: stack-paranoia/arch/i386/mm/pgtable.c
===================================================================
--- stack-paranoia.orig/arch/i386/mm/pgtable.c 2007-04-30 14:43:02.889866227
-0700
+++ stack-paranoia/arch/i386/mm/pgtable.c 2007-04-30 14:57:31.683375948
-0700
@@ -181,6 +181,17 @@
#endif
}
+#ifdef CONFIG_DEBUG_STACK
+unsigned long __kvaddr_to_paddr(unsigned long kvaddr)
+{
+ if (high_memory)
+ BUG_ON(kvaddr >= VMALLOC_START);
+ else
+ BUG_ON(kvaddr >= (unsigned long)__va(MAXMEM));
+ return kvaddr - PAGE_OFFSET;
+}
+#endif /* CONFIG_DEBUG_STACK */
+
pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
{
return (pte_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT|__GFP_ZERO);
Index: stack-paranoia/include/asm-i386/page.h
===================================================================
--- stack-paranoia.orig/include/asm-i386/page.h 2007-04-30 14:43:02.929868507
-0700
+++ stack-paranoia/include/asm-i386/page.h 2007-04-30 14:59:53.799474683
-0700
@@ -118,11 +118,17 @@
#define __PAGE_OFFSET ((unsigned long)CONFIG_PAGE_OFFSET)
#endif
-
#define PAGE_OFFSET ((unsigned long)__PAGE_OFFSET)
+
+#if defined(CONFIG_DEBUG_STACK) && !defined(__ASSEMBLY__)
+unsigned long __kvaddr_to_paddr(unsigned long);
+#define __pa(x) __kvaddr_to_paddr((unsigned long)(x))
+#else /* !CONFIG_DEBUG_STACK */
+#define __pa(x) ((unsigned long)(x)-PAGE_OFFSET)
+#endif /* !CONFIG_DEBUG_STACK */
+
#define VMALLOC_RESERVE ((unsigned long)__VMALLOC_RESERVE)
#define MAXMEM (-__PAGE_OFFSET-__VMALLOC_RESERVE)
-#define __pa(x) ((unsigned long)(x)-PAGE_OFFSET)
/* __pa_symbol should be used for C visible symbols.
This seems to be the official gcc blessed way to do such arithmetic. */
#define __pa_symbol(x) __pa(RELOC_HIDE((unsigned long)(x),0))
-
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