Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init read-only memory

[Michael Ellerman <mpe@ellerman.id.au>]

On Tue, 2015-11-24 at 16:44 -0800, Kees Cook wrote:
> On Tue, Nov 24, 2015 at 4:34 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> > On Nov 24, 2015 1:38 PM, "Kees Cook" <keescook@chromium.org> wrote:
> > > 
> > > One of the easiest ways to protect the kernel from attack is to reduce
> > > the internal attack surface exposed when a "write" flaw is available. By
> > > making as much of the kernel read-only as possible, we reduce the
> > > attack surface.
> > > 
> > > Many things are written to only during __init, and never changed
> > > again. These cannot be made "const" since the compiler will do the wrong
> > > thing (we do actually need to write to them). Instead, move these items
> > > into a memory region that will be made read-only during mark_rodata_ro()
> > > which happens after all kernel __init code has finished.
> > > 
> > > This introduces __read_only as a way to mark such memory, and adds some
> > > documentation about the existing __read_mostly marking.
> > 
> > Obligatory bikeshed:  __ro_after_init, please.  It's barely longer,
> > and it directly explains what's going on.  __read_only makes me think
> > that it's really read-only and could, for example, actually be in ROM.
> 
> I'm fine with that. Anyone else want to chime in before I send a v2?

I'm not clear on why this is x86 only?

It looks like it would work on any arch, or is there some toolchain
requirement?

cheers