Re: [PATCH 10/11] Change mapping of kasan_zero_page int readonly

[Florian Fainelli]

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@xxxxxxxxxxx>
> ---
>  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