On Mon, Jul 1, 2013 at 6:58 AM, Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote:On 6/29/2013 9:05 PM, Kees Cook wrote:
Being able to examine page tables is handy, so make this a module that
can be loaded as needed.
I personally don't think this is a good idea due to the various
security/etc implications of this feature... should really just
be off for non-debug kernels, not "off unless you load the module"
I struggled with this too, but I couldn't come up with any reason that
made sense. If a system is running without modules_disabled, this code
is still loadable:
https://www.outflux.net/blog/archives/2011/04/27/non-executable-kernel-memory-progress/
The root user just needs to look at /proc/kallsyms before passing an
argument. So having it NOT a tristate doesn't actually change anything
except make it awkward to get it done.
If a system is running with verified modules, then just not
signing/including ptdump makes it unavailable. And running with
modules_disabled, obviously, blocks it.
+#ifdef CONFIG_X86_64
+EXPORT_SYMBOL_GPL(init_level4_pgt);
+#else
+EXPORT_SYMBOL_GPL(swapper_pg_dir);
+#endif
like these really have no business in any module
Well, that's why I took me 2 years to send this patch. Those symbols
shouldn't be used outside of page table debugging, so it didn't really
seem upstreamable. However, now that I need to do regular examination
of the page tables, I wanted to do it without the hacky thing above. I
want to do at will on our test images (we use the same kernel for
production and test, but production images leave out the test modules,
etc).