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

[Andrey Konovalov]

On Wed, Nov 7, 2018 at 6:08 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> 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?

Will rename to kasan_early_shadow_page in v11, thanks!

>
> Thanks,
> Mark.