linux-kernel - Re: [PATCH] mm/kasan: Don't vfree() nonexistent vm

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Date:   Mon, 5 Feb 2018 11:48:33 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Paul Menzel <pmenzel+linux-kasan-dev@...gen.mpg.de>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm/kasan: Don't vfree() nonexistent vm_area.



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?
> 

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.