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Date: Thu, 3 Aug 2017 18:06:11 +0300
From: Igor Stoppa <igor.stoppa@...wei.com>
To: Jerome Glisse <jglisse@...hat.com>, Michal Hocko <mhocko@...nel.org>
CC: Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
<linux-security-module@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Kees Cook <keescook@...gle.com>
Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc
allocator
On 03/08/17 17:47, Jerome Glisse wrote:
> On Thu, Aug 03, 2017 at 03:55:50PM +0200, Michal Hocko wrote:
>> On Thu 03-08-17 15:20:31, Igor Stoppa wrote:
[...]
>>> I am confused about this: if "private2" is a pointer, but when I get an
>>> address, I do not even know if the address represents a valid pmalloc
>>> page, how can i know when it's ok to dereference "private2"?
>>
>> because you can make all pages which back vmalloc mappings have vm_area
>> pointer set.
>
> Note that i think this might break some device driver that use vmap()
> i think some of them use private field to store device driver specific
> informations. But there likely is an unuse field in struct page that
> can be use for that.
This increases the unease from my side ... it looks like there is no way
to fully understand if a field is really used or not, without having
deep intimate knowledge of lots of code that is only marginally involved :-/
Similarly, how would I be able to specify what would be the correct way
to decide the member of the union to use for handling the field?
If there were either some sort of non-multiplexed tag/cookie field or a
function, that would specify how to treat the various unions, then it
would be easier to multiplex the remaining data, according to how the
page is used.
--
igor
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