1 files changed, 54 insertions, 6 deletions

diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
index a59db2f08e76..c36e7a3b45e7 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/stackleak.h
@@ -15,19 +15,67 @@
 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
 #include <asm/stacktrace.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 = STACKLEAK_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 == STACKLEAK_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 = (unsigned long)end_of_stack(t) + sizeof(unsigned long);
+	t->lowest_stack = stackleak_task_low_bound(t);
 # ifdef CONFIG_STACKLEAK_METRICS
 	t->prev_lowest_stack = t->lowest_stack;
 # endif
 }
 
-#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE
-int stack_erasing_sysctl(struct ctl_table *table, int write,
-			void *buffer, size_t *lenp, loff_t *ppos);
-#endif
-
 #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
 static inline void stackleak_task_init(struct task_struct *t) { }
 #endif