[PATCH 1/4] kasan: don't tag stacks allocated with pagealloc

[Andrey Konovalov]

This patch prepares Software Tag-Based KASAN for stack tagging support.

With Tag-Based KASAN when kernel stacks are allocated via pagealloc
(which happens when CONFIG_VMAP_STACK is not enabled), they get tagged.
KASAN instrumentation doesn't expect the sp register to be tagged, and
this leads to false-positive reports.

Fix by resetting the tag of kernel stack pointers after allocation.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 kernel/fork.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index d03c9586d342..9cea2265e677 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -261,7 +261,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 					     THREAD_SIZE_ORDER);
 
 	if (likely(page)) {
-		tsk->stack = page_address(page);
+		tsk->stack = kasan_reset_tag(page_address(page));
 		return tsk->stack;
 	}
 	return NULL;
@@ -302,6 +302,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
 {
 	unsigned long *stack;
 	stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
+	stack = kasan_reset_tag(stack);
 	tsk->stack = stack;
 	return stack;
 }
-- 
2.28.0.163.g6104cc2f0b6-goog