On Wed, Nov 25, 2015 at 11:51 PM, Ingo Molnar [off-list ref] wrote:

* Kees Cook [off-list ref] wrote:

quoted

+#ifdef CONFIG_DEBUG_RODATA

Btw., could you please remove the Kconfig option altogether in an additional patch
and make read-only sections an always-on feature? It has been default-y for years
and all distros have it enabled.

Yeah, this is something I've wanted to do for a while, but I would
point out that only a few architectures have actually implemented it,
and for arm and arm64 it was very recent:

$ git grep 'config DEBUG_RODATA'
arch/arm/mm/Kconfig:config DEBUG_RODATA
arch/arm64/Kconfig.debug:config DEBUG_RODATA
arch/parisc/Kconfig.debug:config DEBUG_RODATA
arch/x86/Kconfig.debug:config DEBUG_RODATA

I think s390 already has strict kernel memory permissions, but they
set it up ahead of time. And now, I see in reading the parisc tree,
they do too, and mark_rodata_ro() is effectively a no-op. How does
powerpc handle permissions for kernel rodata?

For parisc (and maybe powerpc and s390) we'll need additional changes
to support __ro_after_init, since they may be making the ro section ro
_before_ init runs. But, that's okay since this series only uses
__ro_after_init on x86 for the moment. ;)

The 'debug rodata' naming is purely historic: this started out as a simple
debugging feature, but meanwhile it has spread and has become an essential kernel
robustness feature.

I agree completely. I suspect I would turn this into
ARCH_HAS_STRICT_KERNMEM or something.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security