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Subject: Re: [PATCH 7/9] Pmalloc Rare Write: modify selected pools
To:     Matthew Wilcox <willy@infradead.org>,
        Igor Stoppa <igor.stoppa@gmail.com>
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        Igor Stoppa <igor.stoppa@huawei.com>,
        Carlos Chinea Perez <carlos.chinea.perez@huawei.com>,
        Remi Denis Courmont <remi.denis.courmont@huawei.com>
References: <20180423125458.5338-1-igor.stoppa@huawei.com>
 <20180423125458.5338-8-igor.stoppa@huawei.com>
 <20180424115050.GD26636@bombadil.infradead.org>
From:   lazytyped <lazytyped@gmail.com>
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Date:   Tue, 24 Apr 2018 14:32:36 +0200
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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.


       -  Enrico