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Subject[PATCH mm v3 22/38] kasan, fork: reset pointer tags of vmapped stacks
From: Andrey Konovalov <>

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

Reset the tag of kernel stack pointers after allocation in

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 register 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 <>


Changes v2->v3:
- Update patch description.
kernel/fork.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 2993a0058f9b..9e488921424e 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;
 \ /
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