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

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Message-ID: <20200309164931.GA23889@roeck-us.net>
Date:   Mon, 9 Mar 2020 09:49:31 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux@...linux.org.uk, Kees Cook <keescook@...omium.org>,
        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 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 ? 

Thanks,
Guenter