From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932225AbcITE6n (ORCPT ); Tue, 20 Sep 2016 00:58:43 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:34149 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750708AbcITE6m (ORCPT ); Tue, 20 Sep 2016 00:58:42 -0400 Date: Mon, 19 Sep 2016 21:58:39 -0700 From: Kees Cook To: Alexander Viro Cc: Linus Torvalds , Josh Poimboeuf , linux-kernel@vger.kernel.org Subject: [INFO] ratio of const vs dynamic usercopy Message-ID: <20160920045839.GA139098@beast> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Al had asked me a couple weeks back what the ratio of const vs dynamic usercopying was. With Josh's cleanup and my fix-up to only call the hardened usercopy when non-const, I can actually gather these statistics on a build. It's a bit of a hack (see attached patch that should not go into the tree), but with my not-very-defconfig, it's rougly 2 to 1 const vs dynamic. However, this doesn't take into account the frequency at _runtime_, which maybe could be discovered via perf comparing copy*user() calls to __check_object_size() calls, but I didn't try that. Does someone have perf setup to check this? $ grep 'warning: call to' build.stderr | wc -l 1505 $ grep 'warning: call to' build.stderr | grep 'const usercopy' | wc -l 998 $ grep 'warning: call to' build.stderr | grep 'dynamic usercopy' | wc -l 507 Signed-off-by: Kees Cook --- include/linux/thread_info.h | 8 +++++++- mm/usercopy.c | 4 ++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 2b5b10eed74f..4cae922797e5 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -115,14 +115,20 @@ static inline int arch_within_stack_frames(const void * const stack, #endif #ifdef CONFIG_HARDENED_USERCOPY -extern void __check_object_size(const void *ptr, unsigned long n, +extern void __compiletime_warning("dynamic usercopy") +__check_object_size(const void *ptr, unsigned long n, bool to_user); +extern void __compiletime_warning("builtin-const usercopy") +__skip_check_object_size(void); + static __always_inline void check_object_size(const void *ptr, unsigned long n, bool to_user) { if (!__builtin_constant_p(n)) __check_object_size(ptr, n, to_user); + else + __skip_check_object_size(); } #else static inline void check_object_size(const void *ptr, unsigned long n, diff --git a/mm/usercopy.c b/mm/usercopy.c index 089328f2b920..9969a06f5e25 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -275,3 +275,7 @@ report: report_usercopy(ptr, n, to_user, err); } EXPORT_SYMBOL(__check_object_size); + +void __skip_check_object_size(void) +{ } +EXPORT_SYMBOL(__skip_check_object_size); -- 2.7.4 -- Kees Cook Nexus Security