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| author | Eric Sandeen <sandeen@sandeen.net> | 2008-04-22 23:38:23 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2008-05-26 16:15:33 +0200 |
| commit | 7c9f8861e6c9c839f913e49b98c3854daca18f27 (patch) | |
| tree | 220b23dff1aa11a83546fbc73a319575ca489188 /kernel/fork.c | |
| parent | stackprotector: turn not having the right gcc into a #warning (diff) | |
| download | linux-7c9f8861e6c9c839f913e49b98c3854daca18f27.tar.xz linux-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.c | 5 |
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(); |