On Wed, Mar 11, 2020 at 11:31:13AM -0700, Guenter Roeck wrote: > 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. Ah, yes, I found it again now too; it went through rmk's tree. For thread posterity: ARM: 8961/2: Fix Kbuild issue caused by per-task stack protector GCC plugin https://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8961/2 -- Kees Cook
