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authorEric Sandeen <sandeen@sandeen.net>2008-04-22 16:38:23 -0500
committerThomas Gleixner <tglx@linutronix.de>2008-05-26 16:15:33 +0200
commit7c9f8861e6c9c839f913e49b98c3854daca18f27 (patch)
tree220b23dff1aa11a83546fbc73a319575ca489188
parentb40a4392a3c262e0d1b5379b4e142a8eefa63439 (diff)
stackprotector: use canary at end of stack to indicate overruns at oops time
(Updated with a common max-stack-used checker that knows about the canary, as suggested by Joe Perches) Use a canary at the end of the stack to clearly indicate at oops time whether the stack has ever overflowed. This is a very simple implementation with a couple of drawbacks: 1) a thread may legitimately use exactly up to the last word on the stack -- but the chances of doing this and then oopsing later seem slim 2) it's possible that the stack usage isn't dense enough that the canary location could get skipped over -- but the worst that happens is that we don't flag the overrun -- though this happens fairly often in my testing :( With the code in place, an intentionally-bloated stack oops might do: BUG: unable to handle kernel paging request at ffff8103f84cc680 IP: [<ffffffff810253df>] update_curr+0x9a/0xa8 PGD 8063 PUD 0 Thread overran stack or stack corrupted Oops: 0000 [1] SMP CPU 0 ... ... unless the stack overrun is so bad that it corrupts some other thread. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--arch/x86/mm/fault.c7
-rw-r--r--include/linux/magic.h1
-rw-r--r--include/linux/sched.h13
-rw-r--r--kernel/exit.c5
-rw-r--r--kernel/fork.c5
-rw-r--r--kernel/sched.c7
6 files changed, 28 insertions, 10 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fd7e1798c75a..1f524df68b96 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -25,6 +25,7 @@
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
+#include <linux/magic.h>
#include <asm/system.h>
#include <asm/desc.h>
@@ -581,6 +582,8 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
unsigned long address;
int write, si_code;
int fault;
+ unsigned long *stackend;
+
#ifdef CONFIG_X86_64
unsigned long flags;
#endif
@@ -850,6 +853,10 @@ no_context:
show_fault_oops(regs, error_code, address);
+ stackend = end_of_stack(tsk);
+ if (*stackend != STACK_END_MAGIC)
+ printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
+
tsk->thread.cr2 = address;
tsk->thread.trap_no = 14;
tsk->thread.error_code = error_code;
diff --git a/include/linux/magic.h b/include/linux/magic.h
index 1fa0c2ce4dec..74e68e201166 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -42,4 +42,5 @@
#define FUTEXFS_SUPER_MAGIC 0xBAD1DEA
#define INOTIFYFS_SUPER_MAGIC 0x2BAD1DEA
+#define STACK_END_MAGIC 0x57AC6E9D
#endif /* __LINUX_MAGIC_H__ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d6a515158783..c5181e77f305 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1969,6 +1969,19 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
extern void thread_info_cache_init(void);
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static inline unsigned long stack_not_used(struct task_struct *p)
+{
+ unsigned long *n = end_of_stack(p);
+
+ do { /* Skip over canary */
+ n++;
+ } while (!*n);
+
+ return (unsigned long)n - (unsigned long)end_of_stack(p);
+}
+#endif
+
/* set thread flags in other task's structures
* - see asm/thread_info.h for TIF_xxxx flags available
*/
diff --git a/kernel/exit.c b/kernel/exit.c
index 8f6185e69b69..fb8de6cbf2c7 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -899,12 +899,9 @@ static void check_stack_usage(void)
{
static DEFINE_SPINLOCK(low_water_lock);
static int lowest_to_date = THREAD_SIZE;
- unsigned long *n = end_of_stack(current);
unsigned long free;
- while (*n == 0)
- n++;
- free = (unsigned long)n - (unsigned long)end_of_stack(current);
+ free = stack_not_used(current);
if (free >= lowest_to_date)
return;
diff --git a/kernel/fork.c b/kernel/fork.c
index 19908b26cf80..d428336e7aa1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -54,6 +54,7 @@
#include <linux/tty.h>
#include <linux/proc_fs.h>
#include <linux/blkdev.h>
+#include <linux/magic.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -186,6 +187,8 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
{
struct task_struct *tsk;
struct thread_info *ti;
+ unsigned long *stackend;
+
int err;
prepare_to_copy(orig);
@@ -211,6 +214,8 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
goto out;
setup_thread_stack(tsk, orig);
+ stackend = end_of_stack(tsk);
+ *stackend = STACK_END_MAGIC; /* for overflow detection */
#ifdef CONFIG_CC_STACKPROTECTOR
tsk->stack_canary = get_random_int();
diff --git a/kernel/sched.c b/kernel/sched.c
index cfa222a91539..a964ed945094 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5748,12 +5748,7 @@ void sched_show_task(struct task_struct *p)
printk(KERN_CONT " %016lx ", thread_saved_pc(p));
#endif
#ifdef CONFIG_DEBUG_STACK_USAGE
- {
- unsigned long *n = end_of_stack(p);
- while (!*n)
- n++;
- free = (unsigned long)n - (unsigned long)end_of_stack(p);
- }
+ free = stack_not_used(p);
#endif
printk(KERN_CONT "%5lu %5d %6d\n", free,
task_pid_nr(p), task_pid_nr(p->real_parent));