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Message-ID: <202003111020.D543B4332@keescook>
Date: Wed, 11 Mar 2020 10:21:20 -0700
From: Kees Cook <keescook@...omium.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux@...linux.org.uk, Emese Revfy <re.emese@...il.com>,
Arnd Bergmann <arnd@...db.de>, Laura Abbott <labbott@...hat.com>,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v3] ARM: smp: add support for per-task stack canaries
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@...linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Emese Revfy <re.emese@...il.com>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Laura Abbott <labbott@...hat.com>
> > Cc: kernel-hardening@...ts.openwall.com
> > Acked-by: Nicolas Pitre <nico@...aro.org>
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> 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
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