[PATCH v3 07/17] scs: add support for stack usage debugging

[samitolvanen]

Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
---
 kernel/scs.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/kernel/scs.c b/kernel/scs.c
index 7780fc4e29ac..67c43af627d1 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -167,6 +167,44 @@ int scs_prepare(struct task_struct *tsk, int node)
 	return 0;
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static inline unsigned long scs_used(struct task_struct *tsk)
+{
+	unsigned long *p = __scs_base(tsk);
+	unsigned long *end = scs_magic(tsk);
+	uintptr_t s = (uintptr_t)p;
+
+	while (p < end && *p)
+		p++;
+
+	return (uintptr_t)p - s;
+}
+
+static void scs_check_usage(struct task_struct *tsk)
+{
+	static DEFINE_SPINLOCK(lock);
+	static unsigned long highest;
+	unsigned long used = scs_used(tsk);
+
+	if (used <= highest)
+		return;
+
+	spin_lock(&lock);
+
+	if (used > highest) {
+		pr_info("%s: highest shadow stack usage %lu bytes\n",
+			__func__, used);
+		highest = used;
+	}
+
+	spin_unlock(&lock);
+}
+#else
+static inline void scs_check_usage(struct task_struct *tsk)
+{
+}
+#endif
+
 bool scs_corrupted(struct task_struct *tsk)
 {
 	return *scs_magic(tsk) != SCS_END_MAGIC;
@@ -181,6 +219,7 @@ void scs_release(struct task_struct *tsk)
 		return;
 
 	WARN_ON(scs_corrupted(tsk));
+	scs_check_usage(tsk);
 
 	scs_account(tsk, -1);
 	task_set_scs(tsk, NULL);
-- 
2.24.0.rc0.303.g954a862665-goog