On Wed, Mar 11, 2020 at 11:47:20AM -0700, Kees Cook wrote: > 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 It's in my fixes branch, waiting for me to do my (now usual) push of fixes to Linus. I'm not sure whether the above discussion is suggesting that there's a problem with this patch, or whether it's trying to encourage me to send it up to Linus. I _think_ there's the suggestion that it causes a regression, hmm? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up
