From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753483AbeA3Wjx (ORCPT ); Tue, 30 Jan 2018 17:39:53 -0500 Received: from terminus.zytor.com ([65.50.211.136]:35185 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752620AbeA3Wju (ORCPT ); Tue, 30 Jan 2018 17:39:50 -0500 Date: Tue, 30 Jan 2018 14:34:18 -0800 From: tip-bot for Dan Williams Message-ID: Cc: dan.j.williams@intel.com, will.deacon@arm.com, tglx@linutronix.de, linux@armlinux.org.uk, cnovikov@lynx.com, mingo@kernel.org, ast@kernel.org, catalin.marinas@arm.com, peterz@infradead.org, torvalds@linux-foundation.org, hpa@zytor.com, linux-kernel@vger.kernel.org Reply-To: peterz@infradead.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, cnovikov@lynx.com, linux@armlinux.org.uk, will.deacon@arm.com, tglx@linutronix.de, dan.j.williams@intel.com, ast@kernel.org, mingo@kernel.org In-Reply-To: <151727414229.33451.18411580953862676575.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151727414229.33451.18411580953862676575.stgit@dwillia2-desk3.amr.corp.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/pti] array_index_nospec: Sanitize speculative array de-references Git-Commit-ID: f3804203306e098dae9ca51540fcd5eb700d7f40 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: f3804203306e098dae9ca51540fcd5eb700d7f40 Gitweb: https://git.kernel.org/tip/f3804203306e098dae9ca51540fcd5eb700d7f40 Author: Dan Williams AuthorDate: Mon, 29 Jan 2018 17:02:22 -0800 Committer: Thomas Gleixner CommitDate: Tue, 30 Jan 2018 21:54:29 +0100 array_index_nospec: Sanitize speculative array de-references array_index_nospec() is proposed as a generic mechanism to mitigate against Spectre-variant-1 attacks, i.e. an attack that bypasses boundary checks via speculative execution. The array_index_nospec() implementation is expected to be safe for current generation CPUs across multiple architectures (ARM, x86). Based on an original implementation by Linus Torvalds, tweaked to remove speculative flows by Alexei Starovoitov, and tweaked again by Linus to introduce an x86 assembly implementation for the mask generation. Co-developed-by: Linus Torvalds Co-developed-by: Alexei Starovoitov Suggested-by: Cyril Novikov Signed-off-by: Dan Williams Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: kernel-hardening@lists.openwall.com Cc: Peter Zijlstra Cc: Catalin Marinas Cc: Will Deacon Cc: Russell King Cc: gregkh@linuxfoundation.org Cc: torvalds@linux-foundation.org Cc: alan@linux.intel.com Link: https://lkml.kernel.org/r/151727414229.33451.18411580953862676575.stgit@dwillia2-desk3.amr.corp.intel.com --- include/linux/nospec.h | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) diff --git a/include/linux/nospec.h b/include/linux/nospec.h new file mode 100644 index 0000000..b99bced --- /dev/null +++ b/include/linux/nospec.h @@ -0,0 +1,72 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright(c) 2018 Linus Torvalds. All rights reserved. +// Copyright(c) 2018 Alexei Starovoitov. All rights reserved. +// Copyright(c) 2018 Intel Corporation. All rights reserved. + +#ifndef _LINUX_NOSPEC_H +#define _LINUX_NOSPEC_H + +/** + * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise + * @index: array element index + * @size: number of elements in array + * + * When @index is out of bounds (@index >= @size), the sign bit will be + * set. Extend the sign bit to all bits and invert, giving a result of + * zero for an out of bounds index, or ~0 if within bounds [0, @size). + */ +#ifndef array_index_mask_nospec +static inline unsigned long array_index_mask_nospec(unsigned long index, + unsigned long size) +{ + /* + * Warn developers about inappropriate array_index_nospec() usage. + * + * Even if the CPU speculates past the WARN_ONCE branch, the + * sign bit of @index is taken into account when generating the + * mask. + * + * This warning is compiled out when the compiler can infer that + * @index and @size are less than LONG_MAX. + */ + if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX, + "array_index_nospec() limited to range of [0, LONG_MAX]\n")) + return 0; + + /* + * Always calculate and emit the mask even if the compiler + * thinks the mask is not needed. The compiler does not take + * into account the value of @index under speculation. + */ + OPTIMIZER_HIDE_VAR(index); + return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1); +} +#endif + +/* + * array_index_nospec - sanitize an array index after a bounds check + * + * For a code sequence like: + * + * if (index < size) { + * index = array_index_nospec(index, size); + * val = array[index]; + * } + * + * ...if the CPU speculates past the bounds check then + * array_index_nospec() will clamp the index within the range of [0, + * size). + */ +#define array_index_nospec(index, size) \ +({ \ + typeof(index) _i = (index); \ + typeof(size) _s = (size); \ + unsigned long _mask = array_index_mask_nospec(_i, _s); \ + \ + BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \ + BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \ + \ + _i &= _mask; \ + _i; \ +}) +#endif /* _LINUX_NOSPEC_H */