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=-20.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 2EE02C4363A for ; Fri, 23 Oct 2020 12:12:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B85B9208E4 for ; Fri, 23 Oct 2020 12:12:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="aI9i0Aa5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S463471AbgJWMMd (ORCPT ); Fri, 23 Oct 2020 08:12:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S463462AbgJWMMc (ORCPT ); Fri, 23 Oct 2020 08:12:32 -0400 Received: from mail-qv1-xf4a.google.com (mail-qv1-xf4a.google.com [IPv6:2607:f8b0:4864:20::f4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 089BBC0613D2 for ; Fri, 23 Oct 2020 05:12:31 -0700 (PDT) Received: by mail-qv1-xf4a.google.com with SMTP id es11so797705qvb.10 for ; Fri, 23 Oct 2020 05:12:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=ouYH/AbpkMNV6tkRrDvFrzxeHdaKqWEGX7QPqZMtewo=; b=aI9i0Aa5WCjKA07HTuWW8FUp7wx+YFaPdUHZTbNXkORhjoo+4gY9P+Njn7vXtPjd98 Lo4GQHkNsI83ZvsDocGxx560+bjwXIg5lJP/eqt4ox7W+is0xIo7AcUoCFHnTxDw8GGo V09Hj183zNECQ1i+9bzz4kZcWGY4HiYvi1R0UbYxs3pvArHYjby//i1nVk1HPl7Q+DEp 0NfxpdizNvMUFMWcwPDb2LNCe6OBJhKDTTx0ifsSafqdTrRUJPn6tUyl1ZiTVWZbPIei 8b2A43tsOgsg7G12PUAlBIhn1qNGsKtUIijLphPQ02Kj4cUUDqiKj45bOINXypsAgExY rL5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=ouYH/AbpkMNV6tkRrDvFrzxeHdaKqWEGX7QPqZMtewo=; b=UkisWMd7JOcq/nPKk1TwtvisLz9Rtg6zza1ErSmfINHR/2C+33jSJoVAY3gQfbBRxu EEGkCmTEPp+e6Zk96lO/WArJ4y+N/DxSUp5ZVjSJ9oB0vqKU0L/QvaYcVtc1lSJm7Xds 0U0gsZsZJwiR+bVTHmiWtrCk4IQ9yWGkdREZtLym6cqih3vy71Dwv2Bv5jaS6GSflL8Z thZeKnIFtm1c53p+/H5p+clSOPkiDPFUuonweJHH2q4egLbJ1xy/SgEdGlfG5nUNOzkC THrQQWrpH83LDIhY8Nf1EkvCqom9RCt6I/j28BA+WtI8SB8VuejM0p4lVAyHRkxTP4Sg H07A== X-Gm-Message-State: AOAM533X9F3lN7VfodS3GhzPz3ZujRfD45+JEduCPa+OfM/DYvW5X/0A TCbArb8Z1QsHHKR6vYv1l3f3v8lkZQ== X-Google-Smtp-Source: ABdhPJxW3pz7jE4MX7asN2BGLqaI1oG3AfmWxPt0T37nonMLsH1u+4rSLQYKcMuRA/L272ajQdGkE+LC+A== Sender: "elver via sendgmr" X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:f693:9fff:fef4:2449]) (user=elver job=sendgmr) by 2002:a0c:8285:: with SMTP id i5mr1932002qva.54.1603455150074; Fri, 23 Oct 2020 05:12:30 -0700 (PDT) Date: Fri, 23 Oct 2020 14:12:24 +0200 Message-Id: <20201023121224.3630272-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.29.0.rc1.297.gfa9743e501-goog Subject: [PATCH] kcsan: Fix encoding masks and regain address bit From: Marco Elver To: elver@google.com, paulmck@kernel.org Cc: mark.rutland@arm.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 64b3c0f2a685..fc5154dd2475 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) { -- 2.29.0.rc1.297.gfa9743e501-goog