[PATCH] mm/kasan: map KASAN zero page read only

[Ard Biesheuvel]

On 6 January 2016 at 20:48, Andrey Ryabinin <ryabinin.a.a at gmail.com> wrote:
> 2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel at linaro.org>:
>> The original x86_64-only version of KASAN mapped its zero page
>> read-only, but this got lost when the code was generalised and
>> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
>> did not exist. It has been added to arm64 in the mean time, so
>> let's use it.
>>
>
> Read-only wasn't lost. Just look at the next line:
>      zero_pte = pte_wrprotect(zero_pte);
>
> PAGE_KERNEL_RO is not available on all architectures, thus it would be better
> to not use it in generic code.
>

OK, I didn't see that. For some reason, it is not working for me on
arm64, though.
I will investigate.

-- 
Ard.


>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  mm/kasan/kasan_init.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
>> index 3f9a41cf0ac6..8726a92604ad 100644
>> --- a/mm/kasan/kasan_init.c
>> +++ b/mm/kasan/kasan_init.c
>> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
>>         pte_t *pte = pte_offset_kernel(pmd, addr);
>>         pte_t zero_pte;
>>
>> -       zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
>> +       zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
>>         zero_pte = pte_wrprotect(zero_pte);
>>
>>         while (addr + PAGE_SIZE <= end) {
>> --
>> 2.5.0
>>