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Message-ID: <20180221013636.GE3728@rh>
Date: Wed, 21 Feb 2018 12:36:36 +1100
From: Dave Chinner <dchinner@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Igor Stoppa <igor.stoppa@...wei.com>, Kees Cook <keescook@...omium.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 Tue, Feb 20, 2018 at 03:56:00PM -0800, Matthew Wilcox wrote:
> On Wed, Feb 21, 2018 at 08:36:04AM +1100, Dave Chinner wrote:
> > FWIW, I'm not wanting to use it to replace static variables. All the
> > structures are dynamically allocated right now, and get assigned to
> > other dynamically allocated pointers. I'd likely split the current
> > structures into a "ro after init" structure and rw structure, so
> > how does the "__ro_after_init" attribute work in that case? Is it
> > something like this?
> >
> > struct xfs_mount {
> > struct xfs_mount_ro{
> > .......
> > } *ro __ro_after_init;
^^^^^^^^
pointer, not embedded structure....
> > ......
>
> No, you'd do:
>
> struct xfs_mount_ro {
> [...]
> };
>
> struct xfs_mount {
> const struct xfs_mount_ro *ro;
> [...]
> };
.... so that's pretty much the same thing :P
> > Also, what compile time checks are in place to catch writes to
> > ro structure members? Is sparse going to be able to check this sort
> > of thing, like is does with endian-specific variables?
>
> Just labelling the pointer const should be enough for the compiler to
> catch unintended writes.
Ok.
> > > I'd be interested to have your review of the pmalloc API, if you think
> > > something is missing, once I send out the next revision.
> >
> > I'll look at it in more depth when it comes past again. :P
>
> I think the key question is whether you want a slab-style interface
> or whether you want a kmalloc-style interface. I'd been assuming
> the former, but Igor has implemented the latter already.
Slabs are rally only useful when you have lots of a specific type of
object. I'm concerned mostly about one-off per-mount point
structures, of which there are relatively few. A heap-like pool per
mount is fine for this.
Cheers,
Dave.
--
Dave Chinner
dchinner@...hat.com
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