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Date: Tue, 20 Feb 2018 19:16:38 +0200
From: Igor Stoppa <igor.stoppa@...wei.com>
To: Laura Abbott <labbott@...hat.com>, Kees Cook <keescook@...omium.org>
CC: Boris Lukashev <blukashev@...pervictus.com>, Christopher Lameter
	<cl@...ux.com>, Matthew Wilcox <willy@...radead.org>, Jann Horn
	<jannh@...gle.com>, Jerome Glisse <jglisse@...hat.com>, Michal Hocko
	<mhocko@...nel.org>, Christoph Hellwig <hch@...radead.org>,
	linux-security-module <linux-security-module@...r.kernel.org>, Linux-MM
	<linux-mm@...ck.org>, kernel list <linux-kernel@...r.kernel.org>, "Kernel
 Hardening" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 4/6] Protectable Memory



On 13/02/18 20:10, Laura Abbott wrote:
> On 02/13/2018 07:20 AM, Igor Stoppa wrote:
>> Why alterations of page properties are not considered a risk and the physmap is?
>> And how would it be easier (i suppose) to attack the latter?
> 
> Alterations are certainly a risk but with the physmap the
> mapping is already there. Find the address and you have
> access vs. needing to actually modify the properties
> then do the access. I could also be complete off base
> on my threat model here so please correct me if I'm
> wrong.

It's difficult for me to comment on this without knowing *how* the
attack would be performed, in your model.

Ex: my expectation is that the attacked has R/W access to kernel data
and has knowledge of the location of static variables.

This is not just a guess, but a real-life scenario, found in attacks
that, among other things, are capable of disabling SELinux, to proceed
toward gaining full root capability.

At that point, I think that variables which are allocated dynamically,
in vmalloc address space, are harder to locate, because of the virtual
mapping and the randomness of the address chosen (this I have not
confirmed yet, but I suppose there is some randomness in picking the
address to assign to a certain allocation request to vmalloc, otherwise,
it could be added).

> I think your other summaries are good points though
> and should go in the cover letter.

Ok, I'm just afraid it risks becoming a lengthy dissertation :-)

--
igor

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