Messages in this thread | | | Date | Mon, 30 Nov 2015 13:52:10 -0800 | Subject | Re: [PATCH v2 1/4] init: create cmdline param to disable readonly | From | Kees Cook <> |
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On Wed, Nov 25, 2015 at 11:51 PM, Ingo Molnar <mingo@kernel.org> wrote: > * Kees Cook <keescook@chromium.org> wrote: >> +#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
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