Re: [PATCH 2/2] sched: BUG when stack end location is over written

On Thu, Sep 04, 2014 at 05:32:31PM +0200, Peter Zijlstra wrote:

On Thu, Sep 04, 2014 at 03:50:24PM +0100, Aaron Tomlin wrote:

quoted

Currently in the event of a stack overrun a call to schedule()
does not check for this type of corruption. This corruption is
often silent and can go unnoticed. However once the corrupted
region is examined at a later stage, the outcome is undefined
and often results in a sporadic page fault which cannot be
handled.

This patch checks for a stack overrun and takes appropriate
action since the damage is already done, there is no point
in continuing.

Signed-off-by: Aaron Tomlin <redacted>
---
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ec1a286..d6af6a0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -2660,6 +2660,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
  */
 static inline void schedule_debug(struct task_struct *prev)
 {
+	if (unlikely(prev != &init_task &&
+		task_stack_end_corrupted(prev)))
+		BUG();

superfluous linebreak, also we appear to have BUG_ON() for situations
just like these.

secondly, while I appreciate the 'feature' you're making schedule()
slower for everybody, what do you propose to do about that?

Understood. I will wrap this with a suitable Kconfig option.

-- 
Aaron Tomlin