linux-kernel - Re: [PATCH v15 5/8] arm64: mte: Enable TCO in functions that can read beyond buffer limits

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Date:   Fri, 12 Mar 2021 15:44:17 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v15 5/8] arm64: mte: Enable TCO in functions that can read
 beyond buffer limits



On 3/12/21 3:29 PM, Catalin Marinas wrote:
> On Fri, Mar 12, 2021 at 03:23:44PM +0000, Vincenzo Frascino wrote:
>> On 3/12/21 3:13 PM, Catalin Marinas wrote:
>>> On Fri, Mar 12, 2021 at 02:22:07PM +0000, Vincenzo Frascino wrote:
>>>> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
>>>> index 9b557a457f24..8603c6636a7d 100644
>>>> --- a/arch/arm64/include/asm/mte.h
>>>> +++ b/arch/arm64/include/asm/mte.h
>>>> @@ -90,5 +90,20 @@ static inline void mte_assign_mem_tag_range(void *addr, size_t size)
>>>>  
>>>>  #endif /* CONFIG_ARM64_MTE */
>>>>  
>>>> +#ifdef CONFIG_KASAN_HW_TAGS
>>>> +/* Whether the MTE asynchronous mode is enabled. */
>>>> +DECLARE_STATIC_KEY_FALSE(mte_async_mode);
>>>> +
>>>> +static inline bool system_uses_mte_async_mode(void)
>>>> +{
>>>> +	return static_branch_unlikely(&mte_async_mode);
>>>> +}
>>>> +#else
>>>> +static inline bool system_uses_mte_async_mode(void)
>>>> +{
>>>> +	return false;
>>>> +}
>>>> +#endif /* CONFIG_KASAN_HW_TAGS */
>>>
>>> You can write this with fewer lines:
>>>
>>> DECLARE_STATIC_KEY_FALSE(mte_async_mode);
>>>
>>> static inline bool system_uses_mte_async_mode(void)
>>> {
>>> 	return IS_ENABLED(CONFIG_KASAN_HW_TAGS) &&
>>> 		static_branch_unlikely(&mte_async_mode);
>>> }
>>>
>>> The compiler will ensure that mte_async_mode is not referred when
>>> !CONFIG_KASAN_HW_TAGS and therefore doesn't need to be defined.
>>
>> Yes, I agree, but I introduce "#ifdef CONFIG_KASAN_HW_TAGS" in the successive
>> patch anyway, according to me the overall code looks more uniform like this. But
>> I do not have a strong opinion or preference on this.
> 
> Ah, yes, I didn't look at patch 6 again as it was already reviewed and I
> forgot the context. Leave it as it is then, my reviewed-by still stands.
> 

Ok, thanks.

-- 
Regards,
Vincenzo