From a70857e46dd13e87ae06bf0e64cb6a2d4f436265 Mon Sep 17 00:00:00 2001
From: Aaron Tomlin <atomlin@redhat.com>
Date: Fri, 12 Sep 2014 14:16:18 +0100
Subject: sched: Add helper for task stack page overrun checking

This facility is used in a few places so let's introduce
a helper function to improve code readability.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: aneesh.kumar@linux.vnet.ibm.com
Cc: dzickus@redhat.com
Cc: bmr@redhat.com
Cc: jcastillo@redhat.com
Cc: oleg@redhat.com
Cc: riel@redhat.com
Cc: prarit@redhat.com
Cc: jgh@redhat.com
Cc: minchan@kernel.org
Cc: mpe@ellerman.id.au
Cc: tglx@linutronix.de
Cc: hannes@cmpxchg.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1410527779-8133-3-git-send-email-atomlin@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 35d0760c..99b2f27 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -507,7 +507,6 @@ bail:
 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 {
 	const struct exception_table_entry *entry;
-	unsigned long *stackend;
 
 	/* Are we prepared to handle this fault?  */
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
@@ -536,8 +535,7 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 		regs->nip);
 
-	stackend = end_of_stack(current);
-	if (*stackend != STACK_END_MAGIC)
+	if (task_stack_end_corrupted(current))
 		printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
 
 	die("Kernel access of bad area", regs, sig);
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index bc23a70..6240bc7 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -648,7 +648,6 @@ no_context(struct pt_regs *regs, unsigned long error_code,
 	   unsigned long address, int signal, int si_code)
 {
 	struct task_struct *tsk = current;
-	unsigned long *stackend;
 	unsigned long flags;
 	int sig;
 
@@ -708,8 +707,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
 
 	show_fault_oops(regs, error_code, address);
 
-	stackend = end_of_stack(tsk);
-	if (*stackend != STACK_END_MAGIC)
+	if (task_stack_end_corrupted(tsk))
 		printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
 
 	tsk->thread.cr2		= address;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 118dca7..18f5262 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2617,6 +2617,8 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
 }
 
 #endif
+#define task_stack_end_corrupted(task) \
+		(*(end_of_stack(task)) != STACK_END_MAGIC)
 
 static inline int object_is_on_stack(void *obj)
 {
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 1636e41..16eddb3 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -170,7 +170,7 @@ check_stack(unsigned long ip, unsigned long *stack)
 			i++;
 	}
 
-	if (*end_of_stack(current) != STACK_END_MAGIC) {
+	if (task_stack_end_corrupted(current)) {
 		print_max_stack();
 		BUG();
 	}
-- 
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