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Subject: Re: [PATCH 19/35] kasan: don't allow SW_TAGS with ARM64_MTE
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Andrey Konovalov <andreyknvl@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <cover.1597425745.git.andreyknvl@google.com>
 <5185661d553238884613a432cf1d71b1480a23ba.1597425745.git.andreyknvl@google.com>
 <20200827080442.GA29264@gaia>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <56ba1b14-36af-31ea-116b-23300525398d@arm.com>
Date:   Thu, 27 Aug 2020 10:54:11 +0100
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Hi Andrey,

On 8/27/20 9:04 AM, Catalin Marinas wrote:
> On Fri, Aug 14, 2020 at 07:27:01PM +0200, Andrey Konovalov wrote:
>> Software tag-based KASAN provides its own tag checking machinery that
>> can conflict with MTE. Don't allow enabling software tag-based KASAN
>> when MTE is enabled.
>>
>> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>> ---
>>  lib/Kconfig.kasan | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index b4cf6c519d71..e500c18cbe79 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -69,6 +69,7 @@ config KASAN_GENERIC
>>  config KASAN_SW_TAGS
>>  	bool "Software tag-based mode"
>>  	depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
>> +	depends on !ARM64_MTE
> 
> I think that's better as:
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 10cf81d70657..736c32bd8905 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -131,7 +131,7 @@ config ARM64
>  	select HAVE_ARCH_JUMP_LABEL
>  	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>  	select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
> -	select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN
> +	select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN && !ARM64_MTE
>  	select HAVE_ARCH_KGDB
>  	select HAVE_ARCH_MMAP_RND_BITS
>  	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
> 

I agree with Catalin here, "select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN &&
!ARM64_MTE" should be sufficient.

-- 
Regards,
Vincenzo