linux-kernel - Re: [PATCH 26/35] kasan, arm64: Enable TBI EL1

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Date:   Thu, 27 Aug 2020 12:13:45 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/35] kasan, arm64: Enable TBI EL1

On Thu, Aug 27, 2020 at 12:05:55PM +0100, Vincenzo Frascino wrote:
> On 8/27/20 11:40 AM, Catalin Marinas wrote:
> > On Fri, Aug 14, 2020 at 07:27:08PM +0200, Andrey Konovalov wrote:
> >> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> >> index 152d74f2cc9c..6880ddaa5144 100644
> >> --- a/arch/arm64/mm/proc.S
> >> +++ b/arch/arm64/mm/proc.S
> >> @@ -38,7 +38,7 @@
> >>  /* PTWs cacheable, inner/outer WBWA */
> >>  #define TCR_CACHE_FLAGS	TCR_IRGN_WBWA | TCR_ORGN_WBWA
> >>  
> >> -#ifdef CONFIG_KASAN_SW_TAGS
> >> +#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
> >>  #define TCR_KASAN_FLAGS TCR_TBI1
> >>  #else
> >>  #define TCR_KASAN_FLAGS 0
> > 
> > I prefer to turn TBI1 on only if MTE is present. So on top of the v8
> > user series, just do this in __cpu_setup.
> 
> Not sure I understand... Enabling TBI1 only if MTE is present would break
> KASAN_SW_TAGS which is based on TBI1 but not on MTE.

You keep the KASAN_SW_TAGS as above but for HW_TAGS, only set TBI1 later
in __cpu_setup().

-- 
Catalin