Re: [PATCH mm v4 22/39] kasan, fork: reset pointer tags of vmapped stacks

Alexander Potapenko
2021-12-21T15:11:53Z

On Mon, Dec 20, 2021 at 11:01 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> 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 403b9dbbfb62..4125373dba4e 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;
> }
> --
> 2.25.1
>

--
Alexander Potapenko
Software Engineer

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