1 files changed, 89 insertions, 0 deletions
diff --git a/include/linux/kstack_erase.h b/include/linux/kstack_erase.h
new file mode 100644
index 000000000000..bf3bf1905557
--- /dev/null
+++ b/include/linux/kstack_erase.h
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_KSTACK_ERASE_H
+#define _LINUX_KSTACK_ERASE_H
+
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+
+/*
+ * Check that the poison value points to the unused hole in the
+ * virtual memory map for your platform.
+ */
+#define KSTACK_ERASE_POISON -0xBEEF
+#define KSTACK_ERASE_SEARCH_DEPTH 128
+
+#ifdef CONFIG_KSTACK_ERASE
+#include <asm/stacktrace.h>
+#include <linux/linkage.h>
+
+/*
+ * The lowest address on tsk's stack which we can plausibly erase.
+ */
+static __always_inline unsigned long
+stackleak_task_low_bound(const struct task_struct *tsk)
+{
+	/*
+	 * The lowest unsigned long on the task stack contains STACK_END_MAGIC,
+	 * which we must not corrupt.
+	 */
+	return (unsigned long)end_of_stack(tsk) + sizeof(unsigned long);
+}
+
+/*
+ * The address immediately after the highest address on tsk's stack which we
+ * can plausibly erase.
+ */
+static __always_inline unsigned long
+stackleak_task_high_bound(const struct task_struct *tsk)
+{
+	/*
+	 * The task's pt_regs lives at the top of the task stack and will be
+	 * overwritten by exception entry, so there's no need to erase them.
+	 */
+	return (unsigned long)task_pt_regs(tsk);
+}
+
+/*
+ * Find the address immediately above the poisoned region of the stack, where
+ * that region falls between 'low' (inclusive) and 'high' (exclusive).
+ */
+static __always_inline unsigned long
+stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
+{
+	const unsigned int depth = KSTACK_ERASE_SEARCH_DEPTH / sizeof(unsigned long);
+	unsigned int poison_count = 0;
+	unsigned long poison_high = high;
+	unsigned long sp = high;
+
+	while (sp > low && poison_count < depth) {
+		sp -= sizeof(unsigned long);
+
+		if (*(unsigned long *)sp == KSTACK_ERASE_POISON) {
+			poison_count++;
+		} else {
+			poison_count = 0;
+			poison_high = sp;
+		}
+	}
+
+	return poison_high;
+}
+
+static inline void stackleak_task_init(struct task_struct *t)
+{
+	t->lowest_stack = stackleak_task_low_bound(t);
+# ifdef CONFIG_KSTACK_ERASE_METRICS
+	t->prev_lowest_stack = t->lowest_stack;
+# endif
+}
+
+asmlinkage void noinstr stackleak_erase(void);
+asmlinkage void noinstr stackleak_erase_on_task_stack(void);
+asmlinkage void noinstr stackleak_erase_off_task_stack(void);
+void __no_caller_saved_registers noinstr __sanitizer_cov_stack_depth(void);
+
+#else /* !CONFIG_KSTACK_ERASE */
+static inline void stackleak_task_init(struct task_struct *t) { }
+#endif
+
+#endif