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Date: Fri, 21 Oct 2016 10:12:11 +0900
From: AKASHI Takahiro <takahiro.akashi@...aro.org>
To: Kees Cook <keescook@...omium.org>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Rusty Russell <rusty@...tcorp.com.au>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] module: extend 'rodata=off' boot
cmdline parameter to module mappings
On Thu, Oct 20, 2016 at 01:48:15PM -0700, Kees Cook wrote:
> On Wed, Oct 19, 2016 at 11:24 PM, AKASHI Takahiro
> <takahiro.akashi@...aro.org> wrote:
> > The current "rodata=off" parameter disables read-only kernel mappings
> > under CONFIG_DEBUG_RODATA:
> > commit d2aa1acad22f ("mm/init: Add 'rodata=off' boot cmdline parameter
> > to disable read-only kernel mappings")
> >
> > This patch is a logical extension to module mappings ie. read-only mappings
> > at module loading can be disabled even if CONFIG_DEBUG_SET_MODULE_RONX
> > (mainly for debug use). Please note, however, that it only affects RO/RW
> > permissions, keeping NX set.
> >
> > This is the first step to make CONFIG_DEBUG_SET_MODULE_RONX mandatory
> > (always-on) in the future as CONFIG_DEBUG_RODATA on x86 and arm64.
> >
> > Suggested-by: Mark Rutland <mark.rutland@....com>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > ---
> > v1:
> > * remove RFC's "module_ronx=" and merge it with "rodata="
> > * always keep NX set if CONFIG_SET_MODULE_RONX
> >
> > include/linux/init.h | 3 ++-
> > init/main.c | 2 +-
> > kernel/module.c | 21 ++++++++++++++++++---
> > 3 files changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/init.h b/include/linux/init.h
> > index e30104c..20aa2eb 100644
> > --- a/include/linux/init.h
> > +++ b/include/linux/init.h
> > @@ -126,7 +126,8 @@ void prepare_namespace(void);
> > void __init load_default_modules(void);
> > int __init init_rootfs(void);
> >
> > -#ifdef CONFIG_DEBUG_RODATA
> > +#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
> > +extern bool rodata_enabled;
> > void mark_rodata_ro(void);
> > #endif
> >
> > diff --git a/init/main.c b/init/main.c
> > index 2858be7..92db2f3 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -915,7 +915,7 @@ static int try_to_run_init_process(const char *init_filename)
> > static noinline void __init kernel_init_freeable(void);
> >
> > #ifdef CONFIG_DEBUG_RODATA
> > -static bool rodata_enabled = true;
> > +bool rodata_enabled = true;
>
> Is there a mismatch here between the extern ifdef and the bool ifdef?
> I.e. shouldn't the ifdef here be || DEBUG_SET_MODULE_RONX too?
Yes.
> Also, can you mark this as __ro_after_init, since nothing changes it
> after the kernel command line is parsed?
Yes, yes.
Thanks,
-Takahiro AKASHI
> Otherwise, this looks fine to me.
>
> -Kees
>
>
> --
> Kees Cook
> Nexus Security
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