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Date:   Fri, 11 Mar 2022 10:34:39 +0000
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc:     linus.walleij@linaro.org, linux-kernel@vger.kernel.org,
        andreyknvl@gmail.com, anshuman.khandual@arm.com, ardb@kernel.org,
        arnd@arndb.de, dvyukov@google.com, geert+renesas@glider.be,
        glider@google.com, kasan-dev@googlegroups.com,
        linux-arm-kernel@lists.infradead.org, lukas.bulwahn@gmail.com,
        mark.rutland@arm.com, masahiroy@kernel.org, matthias.bgg@gmail.com,
        ryabinin.a.a@gmail.com, yj.chiang@mediatek.com
Subject: Re: [PATCH v3 1/2] arm: kasan: support CONFIG_KASAN_VMALLOC
Message-ID: <YislvzIg3Tvwj2+J@shell.armlinux.org.uk>
References: <20220227134726.27584-1-lecopzer.chen@mediatek.com>
 <20220227134726.27584-2-lecopzer.chen@mediatek.com>
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>
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On Sun, Feb 27, 2022 at 09:47:25PM +0800, Lecopzer Chen wrote:
> Simply make shadow of vmalloc area mapped on demand.
> 
> Since the virtual address of vmalloc for Arm is also between
> MODULE_VADDR and 0x100000000 (ZONE_HIGHMEM), which means the shadow
> address has already included between KASAN_SHADOW_START and
> KASAN_SHADOW_END.
> Thus we need to change nothing for memory map of Arm.
> 
> This can fix ARM_MODULE_PLTS with KASan, support KASan for higmem
> and provide the first step to support CONFIG_VMAP_STACK with Arm.
> 
> Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
> ---
>  arch/arm/Kconfig                 |  1 +
>  arch/arm/include/asm/kasan_def.h | 11 ++++++++++-
>  arch/arm/mm/kasan_init.c         |  6 +++++-
>  3 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 4c97cb40eebb..78250e246cc6 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -72,6 +72,7 @@ config ARM
>  	select HAVE_ARCH_KFENCE if MMU && !XIP_KERNEL
>  	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
>  	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
> +	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
>  	select HAVE_ARCH_MMAP_RND_BITS if MMU
>  	select HAVE_ARCH_PFN_VALID
>  	select HAVE_ARCH_SECCOMP
> diff --git a/arch/arm/include/asm/kasan_def.h b/arch/arm/include/asm/kasan_def.h
> index 5739605aa7cf..96fd1d3b5a0c 100644
> --- a/arch/arm/include/asm/kasan_def.h
> +++ b/arch/arm/include/asm/kasan_def.h
> @@ -19,7 +19,16 @@
>   * space to use as shadow memory for KASan as follows:
>   *
>   * +----+ 0xffffffff
> - * |    |							\
> + * |    |\
> + * |    | |-> ZONE_HIGHMEM for vmalloc virtual address space.
> + * |    | |   Such as vmalloc(), GFP_HIGHUSER (__GFP__HIGHMEM),
> + * |    | |   module address using ARM_MODULE_PLTS, etc.
> + * |    | |
> + * |    | |   If CONFIG_KASAN_VMALLOC=y, this area would populate
> + * |    | |   shadow address on demand.
> + * |    |/

This diagram is incorrect. We already have the memory layout in
Documentation/arm/memory.rst, so we don't need another set of
documentation that is misleading.

-- 
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