[PATCH mm] fix for "kasan, fork: reset pointer tags of vmapped stacks"

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

That patch didn't update the case when a stack is retrived from
cached_stacks in alloc_thread_stack_node(). As cached_stacks stores
vm_structs and not stack pointers themselves, the pointer tag needs
to be reset there as well.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 kernel/fork.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 57d624f05182..5e3ad2e7a756 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -226,15 +226,17 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 		if (!s)
 			continue;
 
-		/* Mark stack accessible for KASAN. */
+		/* Reset stack metadata. */
 		kasan_unpoison_range(s->addr, THREAD_SIZE);
 
+		stack = kasan_reset_tag(s->addr);
+
 		/* Clear stale pointers from reused stack. */
-		memset(s->addr, 0, THREAD_SIZE);
+		memset(stack, 0, THREAD_SIZE);
 
 		tsk->stack_vm_area = s;
-		tsk->stack = s->addr;
-		return s->addr;
+		tsk->stack = stack;
+		return stack;
 	}
 
 	/*
-- 
2.25.1