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Date: Mon, 5 Mar 2018 14:29:07 +0000
From: Mark Rutland <mark.rutland@arm.com>
Subject: Re: [RFC PATCH 06/14] khwasan: enable top byte ignore for the kernel
Message-ID: <20180305142907.uvrvwmtfl7o45myf@lakrids.cambridge.arm.com>
References: <cover.1520017438.git.andreyknvl@google.com>
 <739eecf573b6342fc41c4f89d7f64eb8c183e312.1520017438.git.andreyknvl@google.com>
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To: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Jonathan Corbet <corbet@lwn.net>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>, Christopher Li <sparse@chrisli.org>, Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, Masahiro Yamada <yamada.masahiro@socionext.com>, Michal Marek <michal.lkml@markovi.net>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Yury Norov <ynorov@caviumnetworks.com>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Bob Picco <bob.picco@oracle.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Kristina Martsenko <kristina.martsenko@arm.com>, Punit Agrawal <punit.agrawal@arm.com>, Dave Martin <Dave.Martin@arm.com>, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry@arm.com>, Michael Weiser <michael.weiser@gmx.de>, Steve Capper <steve.capper@arm.com>, Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Sandipan Das <sandipan@linux.vnet.ibm.com>, Paul Lawrence <paullawrence@google.com>, David Woodhouse <dwmw@amazon.co.uk>, Kees Cook <keescook@chromium.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Arnd Bergmann <arnd@arndb.de>, kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ext4@vger.kernel.org, linux-sparse@vger.kernel.org, linux-mm@kvack.org, linux-kbuild@vger.kernel.org, Kostya Serebryany <kcc@google.com>, Evgeniy Stepanov <eugenis@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Kees Cook <keescook@google.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>

On Fri, Mar 02, 2018 at 08:44:25PM +0100, Andrey Konovalov wrote:
> +#ifdef CONFIG_KASAN_TAGS
> +#define TCR_TBI_FLAGS (TCR_TBI0 | TCR_TBI1)
> +#else
> +#define TCR_TBI_FLAGS TCR_TBI0
> +#endif

Rather than pulling TBI0 into this, I think it'd make more sense to
have:

#ifdef CONFIG_KASAN_TAGS
#define KASAN_TCR_FLAGS	TCR_TBI1
#else
#define KASAN_TCR_FLAGS
#endif

> +
>  #define MAIR(attr, mt)	((attr) << ((mt) * 8))
>  
>  /*
> @@ -432,7 +438,7 @@ ENTRY(__cpu_setup)
>  	 * both user and kernel.
>  	 */
>  	ldr	x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
> -			TCR_TG_FLAGS | TCR_ASID16 | TCR_TBI0 | TCR_A1
> +			TCR_TG_FLAGS | TCR_ASID16 | TCR_TBI_FLAGS | TCR_A1

... and just append KASAN_TCR_FLAGS to the flags here.

That's roughtly what we do with ENDIAN_SET_EL1 for SCTLR_EL1.

Thanks,
Mark.

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