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Date:	Fri, 19 Sep 2014 04:46:58 -0700
From:	tip-bot for Aaron Tomlin <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, atomlin@...hat.com, viro@...iv.linux.org.uk,
	ddstreet@...e.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
	tglx@...utronix.de, davidlohr@...com, lkundrak@...sk,
	linux-kernel@...r.kernel.org, hpa@...or.com, davem@...emloft.net,
	paulmck@...ux.vnet.ibm.com, keescook@...omium.org, ast@...mgrid.com
Subject: [tip:sched/core] sched: Add default-disabled option to BUG()
  when stack end location is overwritten

Commit-ID:  0d9e26329b0c9263d4d9e0422d80a0e73268c52f
Gitweb:     http://git.kernel.org/tip/0d9e26329b0c9263d4d9e0422d80a0e73268c52f
Author:     Aaron Tomlin <atomlin@...hat.com>
AuthorDate: Fri, 12 Sep 2014 14:16:19 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 19 Sep 2014 12:35:24 +0200

sched: Add default-disabled option to BUG() when stack end location is overwritten

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: aneesh.kumar@...ux.vnet.ibm.com
Cc: dzickus@...hat.com
Cc: bmr@...hat.com
Cc: jcastillo@...hat.com
Cc: oleg@...hat.com
Cc: riel@...hat.com
Cc: prarit@...hat.com
Cc: jgh@...hat.com
Cc: minchan@...nel.org
Cc: mpe@...erman.id.au
Cc: tglx@...utronix.de
Cc: rostedt@...dmis.org
Cc: hannes@...xchg.org
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dan Streetman <ddstreet@...e.org>
Cc: Davidlohr Bueso <davidlohr@...com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Lubomir Rintel <lkundrak@...sk>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1410527779-8133-4-git-send-email-atomlin@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/core.c |  3 +++
 lib/Kconfig.debug   | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4b1ddeb..61ee2b3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2693,6 +2693,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
  */
 static inline void schedule_debug(struct task_struct *prev)
 {
+#ifdef CONFIG_SCHED_STACK_END_CHECK
+	BUG_ON(unlikely(task_stack_end_corrupted(prev)));
+#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..e58163d 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 n
+	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
--
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