[PATCH 08/18] scs: add support for stack usage debugging

[Sami Tolvanen]

Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks.

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

diff --git a/kernel/scs.c b/kernel/scs.c
index 0e3cba49ea1a..1ec5c5a8dfae 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -161,6 +161,44 @@ 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;
@@ -175,6 +213,7 @@ void scs_release(struct task_struct *tsk)
                return;
 
        WARN_ON(scs_corrupted(tsk));
+       scs_check_usage(tsk);
 
        scs_account(tsk, -1);
        scs_task_init(tsk);
-- 
2.23.0.866.gb869b98d4c-goog