On Mon, Jul 1, 2013 at 6:58 AM, Arjan van de Ven <ar...@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). -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
