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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 /kernel/fork.c
parentb40a4392a3c262e0d1b5379b4e142a8eefa63439 (diff)
downloadlwn-7c9f8861e6c9c839f913e49b98c3854daca18f27.tar.gz
lwn-7c9f8861e6c9c839f913e49b98c3854daca18f27.zip
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>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c5
1 files changed, 5 insertions, 0 deletions
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();