[PATCH v6 22/39] kasan, fork: reset pointer tags of vmapped stacks

andrey.konovalov
2022-01-24T18:55:18Z

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
alloc_thread_stack_node().

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 <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

---

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 d75a528f7b21..57d624f05182 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -254,6 +254,7 @@ 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;
}