From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8694C55178 for ; Thu, 5 Nov 2020 22:03:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 969992078E for ; Thu, 5 Nov 2020 22:03:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604613814; bh=Ncz9nvwlkZVwG51mnGlyWz6j4Z0NH0pqXpw92eRR6Lc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=mc2un7Jwva08TK3uAFmEDd+BxJYcpGS697wrSE2KvkHguHMtZcIMMLamQtrpLURkM tTC7OmNIHt22WWDv0HEF3UIf0vG6jx6Fy18WQYXc/HubdQM1tKctW9Ub9KTVllmyTR Nv3b9UYwODyj6wgyCCZF5HrwEksnvHeiYz9tYlTg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732774AbgKEWDd (ORCPT ); Thu, 5 Nov 2020 17:03:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:59914 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732603AbgKEWD1 (ORCPT ); Thu, 5 Nov 2020 17:03:27 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 02F4D21D46; Thu, 5 Nov 2020 22:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604613806; bh=Ncz9nvwlkZVwG51mnGlyWz6j4Z0NH0pqXpw92eRR6Lc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vcVqjhH5UTHOv4DhRyOS3e1KDRBnEUH/YNdLOu5kdiyHCbwCYyrx3D1MlDey1M/ky uv3ePmyMzQ4dCI6oM3/SdztsxdYQD9LUE52LVi+8Ejr9j52VTgDg3oLdk9enErnDxa l+5Mq52pef8/+zD05sMRr6wUAlHksNNCehuoKX4E= From: paulmck@kernel.org To: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, kernel-team@fb.com, mingo@kernel.org Cc: elver@google.com, andreyknvl@google.com, glider@google.com, dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com, "Paul E . McKenney" Subject: [PATCH kcsan 3/3] kcsan: Fix encoding masks and regain address bit Date: Thu, 5 Nov 2020 14:03:24 -0800 Message-Id: <20201105220324.15808-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20201105220302.GA15733@paulmck-ThinkPad-P72> References: <20201105220302.GA15733@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Marco Elver The watchpoint encoding masks for size and address were off-by-one bit each, with the size mask using 1 unnecessary bit and the address mask missing 1 bit. However, due to the way the size is shifted into the encoded watchpoint, we were effectively wasting and never using the extra bit. For example, on x86 with PAGE_SIZE==4K, we have 1 bit for the is-write bit, 14 bits for the size bits, and then 49 bits left for the address. Prior to this fix we would end up with this usage: [ write<1> | size<14> | wasted<1> | address<48> ] Fix it by subtracting 1 bit from the GENMASK() end and start ranges of size and address respectively. The added static_assert()s verify that the masks are as expected. With the fixed version, we get the expected usage: [ write<1> | size<14> | address<49> ] Functionally no change is expected, since that extra address bit is insignificant for enabled architectures. Signed-off-by: Marco Elver Signed-off-by: Paul E. McKenney --- kernel/kcsan/encoding.h | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h index 4f73db6..b50bda9 100644 --- a/kernel/kcsan/encoding.h +++ b/kernel/kcsan/encoding.h @@ -37,14 +37,12 @@ */ #define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS) -/* - * Masks to set/retrieve the encoded data. - */ -#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1) -#define WATCHPOINT_SIZE_MASK \ - GENMASK(BITS_PER_LONG-2, BITS_PER_LONG-2 - WATCHPOINT_SIZE_BITS) -#define WATCHPOINT_ADDR_MASK \ - GENMASK(BITS_PER_LONG-3 - WATCHPOINT_SIZE_BITS, 0) +/* Bitmasks for the encoded watchpoint access information. */ +#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1) +#define WATCHPOINT_SIZE_MASK GENMASK(BITS_PER_LONG-2, BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS) +#define WATCHPOINT_ADDR_MASK GENMASK(BITS_PER_LONG-2 - WATCHPOINT_SIZE_BITS, 0) +static_assert(WATCHPOINT_ADDR_MASK == (1UL << WATCHPOINT_ADDR_BITS) - 1); +static_assert((WATCHPOINT_WRITE_MASK ^ WATCHPOINT_SIZE_MASK ^ WATCHPOINT_ADDR_MASK) == ~0UL); static inline bool check_encodable(unsigned long addr, size_t size) { -- 2.9.5