Re: [PATCH v3] ARM: smp: add support for per-task stack canaries

[Kees Cook]

On Mon, Mar 09, 2020 at 09:49:31AM -0700, Guenter Roeck wrote:
> On Thu, Dec 06, 2018 at 09:32:57AM +0100, Ard Biesheuvel wrote:
> > On ARM, we currently only change the value of the stack canary when
> > switching tasks if the kernel was built for UP. On SMP kernels, this
> > is impossible since the stack canary value is obtained via a global
> > symbol reference, which means
> > a) all running tasks on all CPUs must use the same value
> > b) we can only modify the value when no kernel stack frames are live
> >    on any CPU, which is effectively never.
> > 
> > So instead, use a GCC plugin to add a RTL pass that replaces each
> > reference to the address of the __stack_chk_guard symbol with an
> > expression that produces the address of the 'stack_canary' field
> > that is added to struct thread_info. This way, each task will use
> > its own randomized value.
> > 
> > Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Emese Revfy <re.emese@xxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Laura Abbott <labbott@xxxxxxxxxx>
> > Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx
> > Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> 
> Since this patch is in the tree, cc-option no longer works on
> the arm architecture if CONFIG_STACKPROTECTOR_PER_TASK is enabled.
> 
> Any idea how to fix that ? 

I thought Arnd sent a patch to fix it and it got picked up?

-- 
Kees Cook