2 files changed, 30 insertions, 14 deletions

diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
index 467661aeb413..c36e7a3b45e7 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/stackleak.h
@@ -42,6 +42,32 @@ stackleak_task_high_bound(const struct task_struct *tsk)
 	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 = stackleak_task_low_bound(t);
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index ba346d46218f..afd54b8e10b8 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -74,20 +74,10 @@ static __always_inline void __stackleak_erase(void)
 {
 	const unsigned long task_stack_low = stackleak_task_low_bound(current);
 	const unsigned long task_stack_high = stackleak_task_high_bound(current);
-	unsigned long erase_low = current->lowest_stack;
-	unsigned long erase_high;
-	unsigned int poison_count = 0;
-	const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
-
-	/* Search for the poison value in the kernel stack */
-	while (erase_low > task_stack_low && poison_count <= depth) {
-		if (*(unsigned long *)erase_low == STACKLEAK_POISON)
-			poison_count++;
-		else
-			poison_count = 0;
-
-		erase_low -= sizeof(unsigned long);
-	}
+	unsigned long erase_low, erase_high;
+
+	erase_low = stackleak_find_top_of_poison(task_stack_low,
+						 current->lowest_stack);
 
 #ifdef CONFIG_STACKLEAK_METRICS
 	current->prev_lowest_stack = erase_low;