Functions which the compiler has instrumented for ASAN place poison on the stack shadow upon entry and remove this poison prior to returning. In some cases (e.g. hotplug and idle), CPUs may exit the kernel a number of levels deep in C code. If there are any instrumented functions on this critical path, these will leave portions of the idle thread stack shadow poisoned. If a CPU returns to the kernel via a different path (e.g. a cold entry), then depending on stack frame layout subsequent calls to instrumented functions may use regions of the stack with stale poison, resulting in (spurious) KASAN splats to the console. Contemporary GCCs always add stack shadow poisoning when ASAN is enabled, even when asked to not instrument a function [1], so we can't simply annotate functions on the critical path to avoid poisoning. Instead, this series explicitly removes any stale poison before it can be hit. In the common hotplug case we clear the entire stack shadow in common code, before a CPU is brought online. On architectures which perform a cold return as part of cpu idle may retain an architecture-specific amount of stack contents. To retain the poison for this retained context, the arch code must call the core KASAN code, passing a "watermark" stack pointer value beyond which shadow will be cleared. Architectures which don't perform a cold return as part of idle do not need any additional code. This is a combination of previous approaches [2,3], attempting to keep as much as possible generic. Since v1 [4]: * Clean from task_stack_page(task) * Add acks from v1 Andrew, the conclusion [5] from v1 was that this should go via the mm tree. Are you happy to pick this up? Ingo was happy for the sched patch to go via the arm64 tree, and I assume that also holds for going via mm. Ingo, please shout if that's not the case! Thanks, Mark. [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69863 [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/409466.html [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/411850.html [4] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/413093.html [5] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/413475.html Mark Rutland (3): kasan: add functions to clear stack poison sched/kasan: remove stale KASAN poison after hotplug arm64: kasan: clear stale stack poison arch/arm64/kernel/sleep.S | 4 ++++ include/linux/kasan.h | 6 +++++- kernel/sched/core.c | 3 +++ mm/kasan/kasan.c | 20 ++++++++++++++++++++ 4 files changed, 32 insertions(+), 1 deletion(-) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
