linux-kernel - Re: [PATCH 29/31] kasan, arm64: allow KASAN_VMALLOC with HW

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Date:   Wed, 1 Dec 2021 12:35:22 +0100
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 29/31] kasan, arm64: allow KASAN_VMALLOC with HW_TAGS

On Tue, Nov 30, 2021 at 11:08PM +0100, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> vmalloc tagging support for HW_TAGS KASAN is now complete.
> 
> Allow enabling CONFIG_KASAN_VMALLOC.

This actually doesn't "allow" enabling it, it unconditionally enables it
and a user can't disable CONFIG_KASAN_VMALLOC.

I found some background in acc3042d62cb9 why arm64 wants this.

> Also adjust CONFIG_KASAN_VMALLOC description:
> 
> - Mention HW_TAGS support.
> - Remove unneeded internal details: they have no place in Kconfig
>   description and are already explained in the documentation.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  arch/arm64/Kconfig |  3 +--
>  lib/Kconfig.kasan  | 20 ++++++++++----------
>  2 files changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c05d7a06276f..5981e5460c51 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -205,8 +205,7 @@ config ARM64
>  	select IOMMU_DMA if IOMMU_SUPPORT
>  	select IRQ_DOMAIN
>  	select IRQ_FORCED_THREADING
> -	select KASAN_VMALLOC if KASAN_GENERIC
> -	select KASAN_VMALLOC if KASAN_SW_TAGS
> +	select KASAN_VMALLOC

This produces the following warning when making an arm64 defconfig:

 | WARNING: unmet direct dependencies detected for KASAN_VMALLOC
 |   Depends on [n]: KASAN [=n] && HAVE_ARCH_KASAN_VMALLOC [=y]
 |   Selected by [y]:
 |   - ARM64 [=y]
 | 
 | WARNING: unmet direct dependencies detected for KASAN_VMALLOC
 |   Depends on [n]: KASAN [=n] && HAVE_ARCH_KASAN_VMALLOC [=y]
 |   Selected by [y]:
 |   - ARM64 [=y]

To unconditionally select KASAN_VMALLOC, it should probably be

	select KASAN_VMALLOC if KASAN