Re: [PATCH v10 07/22] kasan: initialize shadow to 0xff for tag-based mode

[Mark Rutland]

On Tue, Nov 06, 2018 at 06:30:22PM +0100, Andrey Konovalov wrote:
> A tag-based KASAN shadow memory cell contains a memory tag, that
> corresponds to the tag in the top byte of the pointer, that points to that
> memory. The native top byte value of kernel pointers is 0xff, so with
> tag-based KASAN we need to initialize shadow memory to 0xff.
> 
> Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
>  arch/arm64/mm/kasan_init.c | 16 ++++++++++++++--
>  include/linux/kasan.h      |  8 ++++++++
>  mm/kasan/common.c          |  3 ++-
>  3 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index 63527e585aac..18ebc8994a7b 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -43,6 +43,15 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
>  	return __pa(p);
>  }
>  
> +static phys_addr_t __init kasan_alloc_raw_page(int node)
> +{
> +	void *p = memblock_alloc_try_nid_raw(PAGE_SIZE, PAGE_SIZE,
> +						__pa(MAX_DMA_ADDRESS),
> +						MEMBLOCK_ALLOC_ACCESSIBLE,
> +						node);
> +	return __pa(p);
> +}
> +
>  static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
>  				      bool early)
>  {
> @@ -88,7 +97,9 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
>  
>  	do {
>  		phys_addr_t page_phys = early ? __pa_symbol(kasan_zero_page)
> -					      : kasan_alloc_zeroed_page(node);
> +					      : kasan_alloc_raw_page(node);
> +		if (!early)
> +			memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
>  		next = addr + PAGE_SIZE;
>  		set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
>  	} while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));
> @@ -138,6 +149,7 @@ asmlinkage void __init kasan_early_init(void)
>  		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
>  	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_START, PGDIR_SIZE));
>  	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
> +
>  	kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
>  			   true);
>  }
> @@ -234,7 +246,7 @@ void __init kasan_init(void)
>  		set_pte(&kasan_zero_pte[i],
>  			pfn_pte(sym_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
>  
> -	memset(kasan_zero_page, 0, PAGE_SIZE);
> +	memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);

If this isn't going to contain zero, can we please have a preparatory
patch renaming this to something which isn't misleading?

Perhaps kasan_common_shadow_page?

Thanks,
Mark.