[kernel-hardening] Re: [RFC][PATCH 2/3] mm/page_poison.c: Enable PAGE_POISONING as a separate option

[Laura Abbott <labbott@redhat.com>]

On 01/25/2016 10:39 PM, Jianyu Zhan wrote:
> On Tue, Jan 26, 2016 at 12:55 AM, Laura Abbott
> <labbott@fedoraproject.org> wrote:
>> --- a/mm/debug-pagealloc.c
>> +++ b/mm/debug-pagealloc.c
>> @@ -8,11 +8,5 @@
>>
>>   void __kernel_map_pages(struct page *page, int numpages, int enable)
>>   {
>> -       if (!page_poisoning_enabled())
>> -               return;
>> -
>> -       if (enable)
>> -               unpoison_pages(page, numpages);
>> -       else
>> -               poison_pages(page, numpages);
>> +       kernel_poison_pages(page, numpages, enable);
>>   }
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 63358d9..c733421 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1002,6 +1002,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
>>                                             PAGE_SIZE << order);
>>          }
>>          arch_free_page(page, order);
>> +       kernel_poison_pages(page, 1 << order, 0);
>>          kernel_map_pages(page, 1 << order, 0);
>>
>>          return true;
>> @@ -1396,6 +1397,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>          set_page_refcounted(page);
>>
>>          arch_alloc_page(page, order);
>> +       kernel_poison_pages(page, 1 << order, 1);
>>          kernel_map_pages(page, 1 << order, 1);
>>          kasan_alloc_pages(page, order);
>>
>
> kernel_map_pages() will fall back to page poisoning scheme for
> !ARCH_SUPPORTS_DEBUG_PAGEALLOC.
>
> IIUC,  calling kernel_poison_pages() before kernel_map_pages() will be
> equivalent to call kernel_poison_pages()
> twice?!
>
>

Yes, you are absolutely right. In the !ARCH_SUPPORTS_DEBUG_PAGEALLOC
case we shouldn't need to do anything in kernel_map_pages.

>
>
> Thanks,
> Jianyu Zhan
>

Thanks,
Laura