From 189af4657186da08a2e79fb8e906cfd82b2ccddc Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Thu, 6 Dec 2018 09:32:57 +0100 Subject: ARM: smp: add support for per-task stack canaries 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 Cc: Kees Cook Cc: Emese Revfy Cc: Arnd Bergmann Cc: Laura Abbott Cc: kernel-hardening@lists.openwall.com Acked-by: Nicolas Pitre Signed-off-by: Ard Biesheuvel Signed-off-by: Kees Cook --- arch/arm/Kconfig | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 91be74d8df65..5c0305585a0a 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1810,6 +1810,21 @@ config XEN help Say Y if you want to run Linux in a Virtual Machine on Xen on ARM. +config STACKPROTECTOR_PER_TASK + bool "Use a unique stack canary value for each task" + depends on GCC_PLUGINS && STACKPROTECTOR && SMP && !XIP_DEFLATED_DATA + select GCC_PLUGIN_ARM_SSP_PER_TASK + default y + help + Due to the fact that GCC uses an ordinary symbol reference from + which to load the value of the stack canary, this value can only + change at reboot time on SMP systems, and all tasks running in the + kernel's address space are forced to use the same canary value for + the entire duration that the system is up. + + Enable this option to switch to a different method that uses a + different canary value for each task. + endmenu menu "Boot options" -- cgit