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Date: Tue, 26 Jan 2016 12:27:35 -0800
From: Laura Abbott <labbott@...hat.com>
To: Jianyu Zhan <nasa4836@...il.com>, Laura Abbott <labbott@...oraproject.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...e.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC][PATCH 2/3] mm/page_poison.c: Enable PAGE_POISONING as a
separate option
On 01/25/2016 10:39 PM, Jianyu Zhan wrote:
> On Tue, Jan 26, 2016 at 12:55 AM, Laura Abbott
> <labbott@...oraproject.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
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