[RFC PATCH] tracing: Add BUG_ON when stack end location is over written

[Aaron Tomlin <atomlin@redhat.com>]

It is difficult to detect a stack overrun when it
actually occurs.

We have observed that this type of corruption is often
silent and can go unnoticed. Once the corrupted region
is examined, the outcome is undefined and often
results in sporadic system crashes.

When the stack tracing feature is enabled, let's check
for this condition and take appropriate action.

Note: init_task doesn't get its stack end location
set to STACK_END_MAGIC.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
 kernel/trace/trace_stack.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index e6be585..21b320e 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -13,6 +13,7 @@
 #include <linux/sysctl.h>
 #include <linux/init.h>
 #include <linux/fs.h>
+#include <linux/magic.h>
 
 #include <asm/setup.h>
 
@@ -144,6 +145,8 @@ check_stack(unsigned long ip, unsigned long *stack)
 			i++;
 	}
 
+	BUG_ON(current != &init_task &&
+		*(end_of_stack(current)) != STACK_END_MAGIC);
  out:
 	arch_spin_unlock(&max_stack_lock);
 	local_irq_restore(flags);
-- 
1.8.5.3