Re: [PATCH] RO/NX protection for loadable kernel modules

From: Ingo Molnar
Date: Tue Jun 23 2009 - 06:01:22 EST

* James Morris <jmorris@xxxxxxxxx> wrote:

> On Thu, 18 Jun 2009, Siarhei Liakh wrote:
> > This patch is a logical extension of the protection provided by
> > CONFIG_DEBUG_RODATA to LKMs. The protection is provided by splitting
> > module_core and module_init into three logical parts each and setting
> > appropriate page access permissions for each individual section:
> >
> > 1. Code: RO+X
> > 2. RO data: RO+NX
> > 3. RW data: RW+NX
> >
> > In order to achieve proper protection, layout_sections() have been
> > modified to align each of the three parts mentioned above onto page
> > boundary. Next, the corresponding page access permissions are set
> > right before successful exit from load_module(). Further,
> > module_free() have been modified to set module_core or module_init as
> > RW+NX right before calling vfree(). Functionality of this patch is
> > enabled only when CONFIG_DEBUG_RODATA defined at compile time.
> >
> This looks potentially useful to me, but I'm not an x86 expert
> (several now added to Cc:).

Pinged a few folks about this already. It looks useful, with the
main worry being:

1) the increase in effective module size (probably worth the price)
2) some uglies in the patch (fixable)

The main ugliness is the excessive use of #ifdefs - those should be
eliminated. Also, most scripts/ warnings about this
patch should be taken seriously.

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