From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751917AbdJZJKB (ORCPT ); Thu, 26 Oct 2017 05:10:01 -0400 Received: from foss.arm.com ([217.140.101.70]:44652 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932301AbdJZJJx (ORCPT ); Thu, 26 Oct 2017 05:09:53 -0400 From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Mark Rutland , Catalin Marinas , Kees Cook , Laura Abbott , Will Deacon Subject: [RFC PATCH 1/2] arm64: write __range_ok() in C Date: Thu, 26 Oct 2017 10:09:41 +0100 Message-Id: <20171026090942.7041-2-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20171026090942.7041-1-mark.rutland@arm.com> References: <20171026090942.7041-1-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently arm64's __range_ok() is written in assembly for efficiency. This hides the logic from the compiler, preventing the compiler from making some optimizations, such as re-ordering instructions or folding multiple calls to __range_ok(). This patch uses GCC's __builtin_uaddl_overflow() to provide an equivalent, efficient check, while giving the compiler the visibility it needs to optimize the check. In testing with v4.14-rc5 using the Linaro 17.05 GCC 6.3.1 toolchain, this has no impact on the kernel Image size, (but results in a smaller vmlinux). Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Kees Cook Cc: Laura Abbott Cc: Will Deacon --- arch/arm64/include/asm/uaccess.h | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index fc0f9eb66039..36f84ec92b9d 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -70,17 +70,20 @@ static inline void set_fs(mm_segment_t fs) * * This needs 65-bit arithmetic. */ +static bool __range_ok_c(unsigned long addr, unsigned long size) +{ + unsigned long result; + + if (__builtin_uaddl_overflow(addr, size, &result)) + return false; + + return result < current_thread_info()->addr_limit; +} + #define __range_ok(addr, size) \ ({ \ - unsigned long __addr = (unsigned long)(addr); \ - unsigned long flag, roksum; \ __chk_user_ptr(addr); \ - asm("adds %1, %1, %3; ccmp %1, %4, #2, cc; cset %0, ls" \ - : "=&r" (flag), "=&r" (roksum) \ - : "1" (__addr), "Ir" (size), \ - "r" (current_thread_info()->addr_limit) \ - : "cc"); \ - flag; \ + __range_ok_c((unsigned long)(addr), (unsigned long)(size)); \ }) /* -- 2.11.0