From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932372AbdJZJKD (ORCPT ); Thu, 26 Oct 2017 05:10:03 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:44664 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932290AbdJZJJ4 (ORCPT ); Thu, 26 Oct 2017 05:09:56 -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 2/2] arm64: allow paranoid __{get,put}user Date: Thu, 26 Oct 2017 10:09:42 +0100 Message-Id: <20171026090942.7041-3-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 Now that the compiler can identify redundant access_ok() checks, we can make __get-user() and __put_user() BUG()-out if there wasn't a preceding access_ok() check. So long as that's in the same compilation unit, the compiler should be able to get rid of the redundant second check and BUG entry. This will allow us to catch __{get,put}_user() calls which did not have a preceding access_ok() check, but may adversely affect a small number of callsites where GCC fails to spot that it can fold two access_ok() checks together. As these checks may impact performance and code size, they are only enabled when CONFIG_ARM64_PARANOID_UACCESS is selected. In testing with v4.14-rc5 with the Linaro 17.05 GCC 6.3.1 toolchain, this makes the kernel Image ~4KiB bigger, and the vmlinux ~93k bigger. I have no performance numbers so far. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Kees Cook Cc: Laura Abbott Cc: Will Deacon --- arch/arm64/Kconfig | 9 +++++++++ arch/arm64/include/asm/uaccess.h | 8 ++++++++ 2 files changed, 17 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 0df64a6a56d4..34df81acda8e 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1028,6 +1028,15 @@ config RANDOMIZE_MODULE_REGION_FULL a limited range that contains the [_stext, _etext] interval of the core kernel, so branch relocations are always in range. +config ARM64_PARANOID_UACCESS + bool "Use paranoid uaccess primitives" + help + Forces access_ok() checks in __get_user(), __put_user(), and other + low-level uaccess primitives which usually do not have checks. This + can limit the effect of missing access_ok() checks in higher-level + primitives, with a runtime performance overhead in some cases and a + small code size overhead. + endmenu menu "Boot options" diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index 36f84ec92b9d..dbe8dfd46ceb 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -195,6 +195,12 @@ static inline void uaccess_enable_not_uao(void) __uaccess_enable(ARM64_ALT_PAN_NOT_UAO); } +#define verify_uaccess(dir, ptr) \ +({ \ + if (IS_ENABLED(CONFIG_ARM64_PARANOID_UACCESS)) \ + BUG_ON(!access_ok(dir, (ptr), sizeof(*(ptr)))); \ +}) + /* * The "__xxx" versions of the user access functions do not verify the address * space - it must have been done previously with a separate "access_ok()" @@ -222,6 +228,7 @@ static inline void uaccess_enable_not_uao(void) do { \ unsigned long __gu_val; \ __chk_user_ptr(ptr); \ + verify_uaccess(VERIFY_READ, ptr); \ uaccess_enable_not_uao(); \ switch (sizeof(*(ptr))) { \ case 1: \ @@ -287,6 +294,7 @@ do { \ do { \ __typeof__(*(ptr)) __pu_val = (x); \ __chk_user_ptr(ptr); \ + verify_uaccess(VERIFY_WRITE, ptr); \ uaccess_enable_not_uao(); \ switch (sizeof(*(ptr))) { \ case 1: \ -- 2.11.0