Re: [PATCH v2 1/4] init: create cmdline param to disable readonly

[Kees Cook]

On Wed, Nov 25, 2015 at 11:51 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> * Kees Cook <keescook@xxxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/