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@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? > Yes, but the fix is not upstream (it is only in -next), and I missed it. Guenter
