Messages in this thread | | | Subject | Re: [PATCH v3] ARM: smp: add support for per-task stack canaries | From | Guenter Roeck <> | Date | Wed, 11 Mar 2020 11:31:13 -0700 |
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On 3/11/20 10:21 AM, Kees Cook wrote: > 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@armlinux.org.uk> >>> Cc: Kees Cook <keescook@chromium.org> >>> Cc: Emese Revfy <re.emese@gmail.com> >>> Cc: Arnd Bergmann <arnd@arndb.de> >>> Cc: Laura Abbott <labbott@redhat.com> >>> Cc: kernel-hardening@lists.openwall.com >>> Acked-by: Nicolas Pitre <nico@linaro.org> >>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.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? >
Yes, but the fix is not upstream (it is only in -next), and I missed it.
Guenter
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