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Subject[PATCH v6 07/15] scs: add support for stack usage debugging
From
Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled,
also prints out the highest shadow stack usage per process.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
kernel/scs.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/kernel/scs.c b/kernel/scs.c
index 5245e992c692..ad74d13f2c0f 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -184,6 +184,44 @@ 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(p);
+ unsigned long s = (unsigned long)p;
+
+ while (p < end && READ_ONCE_NOCHECK(*p))
+ p++;
+
+ return (unsigned long)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 (%d): highest shadow stack usage: %lu bytes\n",
+ tsk->comm, task_pid_nr(tsk), 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)
{
unsigned long *magic = scs_magic(__scs_base(tsk));
@@ -200,6 +238,7 @@ 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);
--
2.24.0.393.g34dc348eaf-goog
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