linux-kernel - Re: [PATCH v4 2/5] kasan: Add KASAN mode kernel parameter

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Date:   Tue, 19 Jan 2021 19:10:20 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>
Subject: Re: [PATCH v4 2/5] kasan: Add KASAN mode kernel parameter

On Mon, Jan 18, 2021 at 7:30 PM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -162,6 +162,9 @@ particular KASAN features.
>
>  - ``kasan=off`` or ``=on`` controls whether KASAN is enabled (default: ``on``).
>
> +- ``kasan.mode=sync`` or ``=async`` controls whether KASAN is configured in
> +  synchronous or asynchronous mode of execution (default: ``sync``).

This needs to be expanded with a short explanation of the difference.

> +static inline void hw_enable_tagging_mode(void)
> +{
> +       if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
> +               hw_enable_tagging_async();
> +       else
> +               hw_enable_tagging_sync();
> +}

It's OK to open-code this in kasan_init_hw_tags_cpu(), no need for an
additional function.

> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -284,7 +284,8 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
>  #define arch_set_mem_tag_range(addr, size, tag) ((void *)(addr))
>  #endif
>
> -#define hw_enable_tagging()                    arch_enable_tagging()
> +#define hw_enable_tagging_sync()               arch_enable_tagging_sync()
> +#define hw_enable_tagging_async()              arch_enable_tagging_async()

This is one of the places that conflicts with the testing patches.
You'll need to: add an else case definition of
hw_enable_tagging_sync(); change lib/test_kasan.c to use
hw_enable_tagging_sync().

I'll later add a patch on top that forbids running the tests with the
async mode.