Re: [PATCH mm 1/2] kasan: don't use read-only static keys

[Marco Elver <elver@google.com>]

On Wed, 9 Dec 2020 at 19:24, Andrey Konovalov <andreyknvl@google.com> wrote:
> __ro_after_init static keys are incompatible with usage in loadable kernel
> modules and cause crashes. Don't use those, use normal static keys.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
>
> This fix can be squashed into
> "kasan: add and integrate kasan boot parameters".
>
> ---
>  mm/kasan/hw_tags.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index c91f2c06ecb5..55bd6f09c70f 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -43,11 +43,11 @@ static enum kasan_arg_stacktrace kasan_arg_stacktrace __ro_after_init;
>  static enum kasan_arg_fault kasan_arg_fault __ro_after_init;
>
>  /* Whether KASAN is enabled at all. */
> -DEFINE_STATIC_KEY_FALSE_RO(kasan_flag_enabled);
> +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);

Side-node: This appears to be just a bad interface; I think the macro
DEFINE_STATIC_KEY_FALSE_RO() is error-prone, if it can't be guaranteed
that this is always safe, since the presence of the macro encourages
its use and we'll inevitably run into this problem again.

>  EXPORT_SYMBOL(kasan_flag_enabled);

DEFINE_STATIC_KEY_FALSE_RO() + EXPORT_SYMBOL() is an immediate bug.
Given its use has not increased substantially since its introduction,
it may be safer to consider its removal.

Thanks,
-- Marco