linux-kernel - [PATCH 3/3] sched: BUG when stack end location is over written

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Message-Id: <1410204197-31204-4-git-send-email-atomlin@redhat.com>
Date:	Mon,  8 Sep 2014 20:23:17 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	peterz@...radead.org
Cc:	mingo@...hat.com, dzickus@...hat.com, bmr@...hat.com,
	jcastillo@...hat.com, atomlin@...hat.com, oleg@...hat.com,
	pzijlstr@...hat.com, riel@...hat.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, x86@...nel.org, rostedt@...dmis.org,
	hannes@...xchg.org, aneesh.kumar@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org, akpm@...gle.com,
	linuxppc-dev@...ts.ozlabs.org, minchan@...nel.org
Subject: [PATCH 3/3] sched: BUG when stack end location is over written

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 <atomlin@...hat.com>
---
 kernel/sched/core.c |  4 ++++
 lib/Kconfig.debug   | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ec1a286..182b2d1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2660,6 +2660,10 @@ static noinline void __schedule_bug(struct task_struct *prev)
  */
 static inline void schedule_debug(struct task_struct *prev)
 {
+#ifdef CONFIG_SCHED_STACK_END_CHECK
+	if (unlikely(task_stack_end_corrupted(prev)))
+		BUG();
+#endif
 	/*
 	 * Test if we are atomic. Since do_exit() needs to call into
 	 * schedule() atomically, we ignore that path. Otherwise whine
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index a285900..2a8280a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -824,6 +824,18 @@ config SCHEDSTATS
 	  application, you can say N to avoid the very slight overhead
 	  this adds.
 
+config SCHED_STACK_END_CHECK
+	bool "Detect stack corruption on calls to schedule()"
+	depends on DEBUG_KERNEL
+	default y
+	help
+	  This option checks for a stack overrun on calls to schedule().
+	  If the stack end location is found to be over written always panic as
+	  the content of the corrupted region can no longer be trusted.
+	  This is to ensure no erroneous behaviour occurs which could result in
+	  data corruption or a sporadic crash at a later stage once the region
+	  is examined. The runtime overhead introduced is minimal.
+
 config TIMER_STATS
 	bool "Collect kernel timers statistics"
 	depends on DEBUG_KERNEL && PROC_FS
-- 
1.9.3

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