init/main.c: Give init_task a canary

Tasks get their end of stack set to STACK_END_MAGIC with the
aim to catch stack overruns. Currently this feature does not
apply to init_task. This patch removes this restriction.

Note that a similar patch was posted by Prarit Bhargava
some time ago but was never merged:

  http://marc.info/?l=linux-kernel&m=127144305403241&w=2

Signed-off-by: Aaron Tomlin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Alex Thorlton <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Daeseok Youn <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Fabian Frederick <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Michael Opdenacker <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Seiji Aguchi <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Yasuaki Ishimatsu <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

2 files changed, 10 insertions, 6 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 9387ae8ab048..ad64248c4b18 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -294,11 +294,18 @@ int __weak arch_dup_task_struct(struct task_struct *dst,
 	return 0;
 }
 
+void set_task_stack_end_magic(struct task_struct *tsk)
+{
+	unsigned long *stackend;
+
+	stackend = end_of_stack(tsk);
+	*stackend = STACK_END_MAGIC;	/* for overflow detection */
+}
+
 static struct task_struct *dup_task_struct(struct task_struct *orig)
 {
 	struct task_struct *tsk;
 	struct thread_info *ti;
-	unsigned long *stackend;
 	int node = tsk_fork_get_node(orig);
 	int err;
 
@@ -328,8 +335,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
 	setup_thread_stack(tsk, orig);
 	clear_user_return_notifier(tsk);
 	clear_tsk_need_resched(tsk);
-	stackend = end_of_stack(tsk);
-	*stackend = STACK_END_MAGIC;	/* for overflow detection */
+	set_task_stack_end_magic(tsk);
 
 #ifdef CONFIG_CC_STACKPROTECTOR
 	tsk->stack_canary = get_random_int();
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 8a4e5cb66a4c..1636e41828c2 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -13,7 +13,6 @@
 #include <linux/sysctl.h>
 #include <linux/init.h>
 #include <linux/fs.h>
-#include <linux/magic.h>
 
 #include <asm/setup.h>
 
@@ -171,8 +170,7 @@ check_stack(unsigned long ip, unsigned long *stack)
 			i++;
 	}
 
-	if ((current != &init_task &&
-		*(end_of_stack(current)) != STACK_END_MAGIC)) {
+	if (*end_of_stack(current) != STACK_END_MAGIC) {
 		print_max_stack();
 		BUG();
 	}