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From:   Marco Elver <elver@google.com>
Date:   Wed, 9 Dec 2020 19:49:36 +0100
Message-ID: <CANpmjNMf1tOYTFojUQrHoscFxPPEed_vkBufgxVLduQ6dBvCUA@mail.gmail.com>
Subject: Re: [PATCH mm 1/2] kasan: don't use read-only static keys
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>
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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