linux-kernel - Re: [RFC PATCH v16 0/6] mm: security: ro protection for dynamic data

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Date:   Tue, 20 Feb 2018 12:21:11 +1100
From:   Dave Chinner <dchinner@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Igor Stoppa <igor.stoppa@...wei.com>,
        Matthew Wilcox <willy@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Hocko <mhocko@...nel.org>,
        Laura Abbott <labbott@...hat.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christoph Lameter <cl@...ux.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC PATCH v16 0/6] mm: security: ro protection for dynamic data

On Mon, Feb 12, 2018 at 03:32:36PM -0800, Kees Cook wrote:
> On Mon, Feb 12, 2018 at 8:52 AM, Igor Stoppa <igor.stoppa@...wei.com> wrote:
> > This patch-set introduces the possibility of protecting memory that has
> > been allocated dynamically.
> >
> > The memory is managed in pools: when a memory pool is turned into R/O,
> > all the memory that is part of it, will become R/O.
> >
> > A R/O pool can be destroyed, to recover its memory, but it cannot be
> > turned back into R/W mode.
> >
> > This is intentional. This feature is meant for data that doesn't need
> > further modifications after initialization.
> 
> This series came up in discussions with Dave Chinner (and Matthew
> Wilcox, already part of the discussion, and others) at LCA. I wonder
> if XFS would make a good initial user of this, as it could allocate
> all the function pointers and other const information about a
> superblock in pmalloc(), keeping it separate from the R/W portions?
> Could other filesystems do similar things?

I wasn't cc'd on this patchset, (please use david@...morbit.com for
future postings) so I can't really say anything about it right
now. My interest for XFS was that we have a fair amount of static
data in XFS that we set up at mount time and it never gets modified
after that. I'm not so worried about VFS level objects (that's a
much more complex issue) but there is a lot of low hanging fruit in
the XFS structures we could convert to write-once structures.

Cheers,

Dave.
-- 
Dave Chinner
dchinner@...hat.com