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

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Message-ID: <20210312152927.GD24210@arm.com>
Date:   Fri, 12 Mar 2021 15:29:28 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....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 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.

-- 
Catalin