[PATCH 21/31] kasan, fork: don't tag stacks allocated with vmalloc

[andrey.konovalov at linux.dev]

From: Andrey Konovalov <andreyknvl at google.com>

Once tag-based KASAN modes start tagging vmalloc() allocations,
kernel stacks will start getting tagged if CONFIG_VMAP_STACK is enabled.

Reset the tag of kernel stack pointers after allocation.

For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the
instrumentation can't handle the sp register being tagged.

For HW_TAGS KASAN, there's no instrumentation-related issues. However,
the impact of having a tagged SP pointer needs to be properly evaluated,
so keep it non-tagged for now.

Note, that the memory for the stack allocation still gets tagged to
catch vmalloc-into-stack out-of-bounds accesses.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
---
 kernel/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 3244cc56b697..062d1484ef42 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -253,6 +253,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 	 * so cache the vm_struct.
 	 */
 	if (stack) {
+		stack = kasan_reset_tag(stack);
 		tsk->stack_vm_area = find_vm_area(stack);
 		tsk->stack = stack;
 	}
-- 
2.25.1