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Subject: Re: [PATCH] mm/kasan: Don't vfree() nonexistent vm_area.
References: <12c9e499-9c11-d248-6a3f-14ec8c4e07f1@molgen.mpg.de>
 <20180201163349.8700-1-aryabinin@virtuozzo.com>
 <20180201195757.GC20742@bombadil.infradead.org>
 <e1cf8e8e-4cc4-ff4f-92e1-f6fcf373c67f@virtuozzo.com>
 <20180202172027.GB16840@bombadil.infradead.org>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <5ea1af5e-213d-5881-652a-c3f2c535254a@virtuozzo.com>
Date: Mon, 5 Feb 2018 11:48:33 +0300
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Sender: owner-linux-mm@kvack.org
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To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Paul Menzel <pmenzel+linux-kasan-dev@molgen.mpg.de>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org



On 02/02/2018 08:20 PM, Matthew Wilcox wrote:
> On Thu, Feb 01, 2018 at 11:22:55PM +0300, Andrey Ryabinin wrote:
>>>> +		vm = find_vm_area((void *)shadow_start);
>>>> +		if (vm)
>>>> +			vfree((void *)shadow_start);
>>>> +	}
>>>
>>> This looks like a complicated way to spell 'is_vmalloc_addr' ...
>>>
>>
>> It's not. shadow_start is never vmalloc address.
> 
> I'm confused.  How can you call vfree() on something that isn't a vmalloc
> address?
> 

a??vfree() is able to free any address returned by __vmalloc_node_range().
And __vmalloc_node_range() gives you any address you ask.
It doesn't have to be an address in [VMALLOC_START, VMALLOC_END] range.

That's also how the module_alloc()/module_memfree() works on architectures that
have designated area for modules.

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