Re: [PATCH mm v3 23/38] kasan, arm64: reset pointer tags of vmapped stacks

[Andrey Konovalov <andreyknvl@gmail.com>]

On Mon, Dec 13, 2021 at 10:54 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
> arch_alloc_vmap_stack().
>
> 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>
>
> ---
>
> Changes v2->v3:
> - Add this patch.
> ---
>  arch/arm64/include/asm/vmap_stack.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/vmap_stack.h b/arch/arm64/include/asm/vmap_stack.h
> index 894e031b28d2..20873099c035 100644
> --- a/arch/arm64/include/asm/vmap_stack.h
> +++ b/arch/arm64/include/asm/vmap_stack.h
> @@ -17,10 +17,13 @@
>   */
>  static inline unsigned long *arch_alloc_vmap_stack(size_t stack_size, int node)
>  {
> +       void *p;
> +
>         BUILD_BUG_ON(!IS_ENABLED(CONFIG_VMAP_STACK));
>
> -       return __vmalloc_node(stack_size, THREAD_ALIGN, THREADINFO_GFP, node,
> +       p = __vmalloc_node(stack_size, THREAD_ALIGN, THREADINFO_GFP, node,
>                         __builtin_return_address(0));
> +       return kasan_reset_tag(p);
>  }
>
>  #endif /* __ASM_VMAP_STACK_H */
> --
> 2.25.1
>

Catalin, Vincenzo,

This is a new patch added in v3. Could you PTAL? Thanks!