Re: [PATCH] [RFC]arm64:Mark __stack_chk_guard as __ro_after_init

[ashimida]

Hi King, Rutland:

Thanks for the reply and let me understand the reason here.

Then may I first submit a patch to modify the attributes of
__stack_chk_guard of the arm/aarch64 platform?

On 9/14/21 6:17 PM, Mark Rutland wrote:
> On Tue, Sep 14, 2021 at 05:44:02PM +0800, Dan Li wrote:
> > __stack_chk_guard is setup once while init stage and never changed
> > after that.
> >
> > Although the modification of this variable at runtime will usually
> > cause the kernel to crash (so dose the attacker), it should be marked
> > as _ro_after_init, and it should not affect performance if it is
> > placed in the ro_after_init section.
> >
> > This should also be the case on the ARM platform, or am I missing
> > something?
> >
> > Signed-off-by: Dan Li <ashimida@xxxxxxxxxxxxxxxxx>
>
> FWIW, this makes sense to me:
>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
>
> Looking at the history, this was added to arm64 in commit:
>
>    c0c264ae5112d1cd ("arm64: Add CONFIG_CC_STACKPROTECTOR")
>
> ... whereas __ro_after_init was introduced around 2 years later in
> commit:
>
>    c74ba8b3480da6dd ("arch: Introduce post-init read-only memory")
>
> ... so we weren't deliberately avoiding __ro_after_init, and there are
> probably a significant number of other variables we could apply it to.
>
> Mark.
>
> > ---
> >   arch/arm64/kernel/process.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index c8989b9..c858b85 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > @@ -60,7 +60,7 @@
> >   
> >   #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
> >   #include <linux/stackprotector.h>
> > -unsigned long __stack_chk_guard __read_mostly;
> > +unsigned long __stack_chk_guard __ro_after_init;
> >   EXPORT_SYMBOL(__stack_chk_guard);
> >   #endif
> >   
> > --
> > 2.7.4