linux-kernel - Re: [PATCH 10/11] Change mapping of kasan_zero

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Message-ID: <c59a7a5a-8168-8409-228a-0e4f841ced98@gmail.com>
Date:   Wed, 11 Oct 2017 12:19:13 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Abbott Liu <liuwenliang@...wei.com>, linux@...linux.org.uk,
        aryabinin@...tuozzo.com, afzal.mohd.ma@...il.com,
        labbott@...hat.com, kirill.shutemov@...ux.intel.com,
        mhocko@...e.com, cdall@...aro.org, marc.zyngier@....com,
        catalin.marinas@....com, akpm@...ux-foundation.org,
        mawilcox@...rosoft.com, tglx@...utronix.de, thgarnie@...gle.com,
        keescook@...omium.org, arnd@...db.de, vladimir.murzin@....com,
        tixy@...aro.org, ard.biesheuvel@...aro.org, robin.murphy@....com,
        mingo@...nel.org, grygorii.strashko@...aro.org
Cc:     glider@...gle.com, dvyukov@...gle.com, opendmb@...il.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        jiazhenghua@...wei.com, dylix.dailei@...wei.com,
        zengweilin@...wei.com, heshaoliang@...wei.com
Subject: Re: [PATCH 10/11] Change mapping of kasan_zero_page int readonly

On 10/11/2017 01:22 AM, Abbott Liu wrote:
>  Because the kasan_zero_page(which is used as the shadow
>  region for some memory that KASan doesn't need to track.) won't be writen
>  after kasan_init, so change the mapping of kasan_zero_page into readonly.
> 
> Cc: Andrey Ryabinin <a.ryabinin@...sung.com>
> ---
>  arch/arm/mm/kasan_init.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm/mm/kasan_init.c b/arch/arm/mm/kasan_init.c
> index 7cfdc39..c11826a 100644
> --- a/arch/arm/mm/kasan_init.c
> +++ b/arch/arm/mm/kasan_init.c
> @@ -200,6 +200,7 @@ void __init kasan_init(void)
>  {
>  	struct memblock_region *reg;
>  	u64 orig_ttbr0;
> +	int i;

Nit: unsigned int i.

>  
>  	orig_ttbr0 = cpu_get_ttbr(0);
>  
> @@ -243,6 +244,17 @@ void __init kasan_init(void)
>  	create_mapping((unsigned long)kasan_mem_to_shadow((void *)MODULES_VADDR),
>  		(unsigned long)kasan_mem_to_shadow((void *)(PKMAP_BASE+PMD_SIZE)),
>  		NUMA_NO_NODE);
> +
> +	/*
> +	 * KAsan may reuse the contents of kasan_zero_pte directly, so we
> +	 * should make sure that it maps the zero page read-only.
> +	 */
> +	for (i = 0; i < PTRS_PER_PTE; i++)
> +                set_pte_at(&init_mm, KASAN_SHADOW_START + i*PAGE_SIZE,
> +                        &kasan_zero_pte[i], pfn_pte(
> +                                virt_to_pfn(kasan_zero_page),
> +                                __pgprot(_L_PTE_DEFAULT | L_PTE_DIRTY | L_PTE_XN | L_PTE_RDONLY)));
> +	memset(kasan_zero_page, 0, PAGE_SIZE);



>  	cpu_set_ttbr0(orig_ttbr0);
>  	flush_cache_all();
>  	local_flush_bp_all();
> 


-- 
Florian