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Date: Tue, 24 Apr 2018 16:39:11 +0400
From: Igor Stoppa <igor.stoppa@...il.com>
To: lazytyped <lazytyped@...il.com>, Matthew Wilcox <willy@...radead.org>
Cc: keescook@...omium.org, paul@...l-moore.com, sds@...ho.nsa.gov,
mhocko@...nel.org, corbet@....net, labbott@...hat.com, david@...morbit.com,
rppt@...ux.vnet.ibm.com, linux-security-module@...r.kernel.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com, Igor Stoppa <igor.stoppa@...wei.com>,
Carlos Chinea Perez <carlos.chinea.perez@...wei.com>,
Remi Denis Courmont <remi.denis.courmont@...wei.com>
Subject: Re: [PATCH 7/9] Pmalloc Rare Write: modify selected pools
On 24/04/18 16:32, lazytyped wrote:
>
>
> On 4/24/18 1:50 PM, Matthew Wilcox wrote:
>> struct modifiable_data {
>> struct immutable_data *d;
>> ...
>> };
>>
>> Then allocate a new pool, change d and destroy the old pool.
>
> With the above, you have just shifted the target of the arbitrary write
> from the immutable data itself to the pointer to the immutable data, so
> got no security benefit.
>
> The goal of the patch is to reduce the window when stuff is writeable,
> so that an arbitrary write is likely to hit the time when data is read-only.
Indeed, that was my - poorly explained, I admit it - idea.
For example, that's the reason why I am remapping one page at a time in
a loop, instead of doing the whole array, to limit exposure and increase
randomness.
WRT the implementation, I'm sure there are bugs that need squashing.
But if I have overlooked some aspect in the overall design, I need
guidance, because i still do not see what I am missing :-(
--
igor
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