linux-kernel - Re: [PATCH v4 1/3] PM / Hibernate: prepare for SANITIZE_FREED

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Date:	Mon, 18 May 2015 12:23:00 +0200
From:	Anisse Astier <anisse@...ier.eu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>,
	Andi Kleen <andi@...stfloor.org>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] PM / Hibernate: prepare for SANITIZE_FREED_PAGES

Hi Rafael,

Thanks for taking the time to review this.

On Sat, May 16, 2015 at 2:28 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Thursday, May 14, 2015 04:19:46 PM Anisse Astier wrote:
>> SANITIZE_FREED_PAGES feature relies on having all pages going through
>> the free_pages_prepare path in order to be cleared before being used. In
>> the hibernate use case, free pages will automagically appear in the
>> system without being cleared, left there by the loading kernel.
>>
>> This patch will make sure free pages are cleared on resume; when we'll
>> enable SANITIZE_FREED_PAGES. We free the pages just after resume because
>> we can't do it later: going through any device resume code might
>> allocate some memory and invalidate the free pages bitmap.
>>
>> Signed-off-by: Anisse Astier <anisse@...ier.eu>
>> ---
>>  kernel/power/hibernate.c |  4 +++-
>>  kernel/power/power.h     |  2 ++
>>  kernel/power/snapshot.c  | 22 ++++++++++++++++++++++
>>  3 files changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index 2329daa..0a73126 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -305,9 +305,11 @@ static int create_image(int platform_mode)
>>                       error);
>>       /* Restore control flow magically appears here */
>>       restore_processor_state();
>> -     if (!in_suspend)
>> +     if (!in_suspend) {
>>               events_check_enabled = false;
>>
>> +             clear_free_pages();
>
> Again, why don't you do that at the swsusp_free() time?

Because it's too late, the kernel has already been through device
resume code, and the free pages bitmap isn't valid anymore; device
resume code might allocate memory, and we'd be clearing those pages as
well.


>> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
>> index 5235dd4..2335130 100644
>> --- a/kernel/power/snapshot.c
>> +++ b/kernel/power/snapshot.c
>> @@ -1032,6 +1032,28 @@ void free_basic_memory_bitmaps(void)
>>       pr_debug("PM: Basic memory bitmaps freed\n");
>>  }
>>
>> +void clear_free_pages(void)
>> +{
>> +#ifdef CONFIG_SANITIZE_FREED_PAGES
>> +     struct memory_bitmap *bm = free_pages_map;
>> +     unsigned long pfn;
>> +
>> +     if (WARN_ON(!(free_pages_map)))
>
> One paren too many.

Thanks, will be fixed.

>
>> +             return;
>> +
>> +     memory_bm_position_reset(bm);
>> +     pfn = memory_bm_next_pfn(bm);
>> +     while (pfn != BM_END_OF_MAP) {
>> +             if (pfn_valid(pfn))
>> +                     clear_highpage(pfn_to_page(pfn));
>
> Is clear_highpage() also fine for non-highmem pages?
>

Yes, it works fine for low memory too because kmap_atomic will just
return the page address if it's already mapped.

Regards,

Anisse
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