Messages in this thread | | | Date | Mon, 1 Jul 2013 09:56:21 -0700 | Subject | Re: [PATCH] x86, kernel: make dump_pagetables a tristate | From | Kees Cook <> |
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On Mon, Jul 1, 2013 at 9:35 AM, Arjan van de Ven <arjan@linux.intel.com> wrote: > On 7/1/2013 8:55 AM, Kees Cook wrote: >> >> On Mon, Jul 1, 2013 at 6:58 AM, Arjan van de Ven <arjan@linux.intel.com> >> 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). > > > the code is small... > how about making it a command line option to enable? > > rather than making something like this a module
Hmm. The Chrome OS build infrastructure frowns on making cmdline changes between production and testing images. I could probably do it this way, but it'd be more of a pain to maintain than just carrying the hack patch.
Since there's no actual loss to system security by making this a module, how about we allow it to be a tristate and continue to recommend it being "n" by default?
As far as the export goes, could ptdump read cr3 instead of needing a symbol export?
-Kees
-- Kees Cook Chrome OS Security
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