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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 794EFC433E0 for ; Thu, 28 Jan 2021 06:59:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D5DC64DCE for ; Thu, 28 Jan 2021 06:59:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231269AbhA1G7N (ORCPT ); Thu, 28 Jan 2021 01:59:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229551AbhA1G7J (ORCPT ); Thu, 28 Jan 2021 01:59:09 -0500 Received: from mail-pf1-x42c.google.com (mail-pf1-x42c.google.com [IPv6:2607:f8b0:4864:20::42c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2B34C061573 for ; Wed, 27 Jan 2021 22:58:29 -0800 (PST) Received: by mail-pf1-x42c.google.com with SMTP id u67so3403844pfb.3 for ; Wed, 27 Jan 2021 22:58:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=o59VmeBiIuFDw0ib/euYCaS+FPmTbZ3Wy7mxU6VxEFA=; b=XRYOapf4k9neRcuuyZn8wIKySdlonzN/xJZFW3n060szEbe9KMqd84pXm10LkyRu2b 5FlaEzhKCdrPjm+Bjigdi+kkbMgVUp/8grReOSLAY/3TNhBGQJZfj9Kik8lXL9qSon6Q H3PkKOxCO+Uok+Jw4awch4Yp1ZO/2vB3pA2uSn7yobtIh2belY6RLtM2s7n55vIBUfod A0IqwnxcXk3LtcPh5sVmAku451HpUahZQvbZdIKaalckY+1Z4vN3avgnwJh3+A43h6AH JL1EoM0oKZ2jrywiktCP9WCms/qy/ai7kGN/+Q4hq8Iac0UUUdux8+9OIM6rpIg1a/MQ wXYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=o59VmeBiIuFDw0ib/euYCaS+FPmTbZ3Wy7mxU6VxEFA=; b=PszPOdul/GdoQ6B3JfW6eGtt/3yW5zLvfpjM2APRXmLUt+Tc90y9oV7JHI7AVGJHia sJlyYfoJqUx2d8e7gZnbnDotyVtYewCmNgExJcuV9mXKo6PQgjc1+fKeEUyNsGgaGP9h mERyt6+B3uXZ1PM5sADOVBCZiX36xHxNqhEgYXg7WgbzCuxA0aXpf9x12qUmSXDSVGzG OmqXJA6fxsO1kSXYUtpygMxJaP0gIz+vwo+8JKNwVypaCRJIPw8lYAV08Zi9UtqbggY1 meiPK3F2/B20Wy/4uQCtzRPedX/ftnIkwWpTgLIoxv80AginmwQhDsNWxg0uU+A1OSP/ bXsg== X-Gm-Message-State: AOAM532TIgeoiLF+MhNSTyQ9nmEblJoZvAmbkd41qzjCgfOP6VZj82ig 1j6nkMEaGqJACLdYIGnwezG0L1YBVakdNRe0 X-Google-Smtp-Source: ABdhPJzdTZpj9coUjBT9+GTgAYnlZj14z4o+uN6Kd/zambD35i7Gejr1ZOV8+GuuUqbSj6Y8MeYLlw== X-Received: by 2002:a05:6a00:2281:b029:1bb:15d2:3b9f with SMTP id f1-20020a056a002281b02901bb15d23b9fmr14295810pfe.25.1611817109179; Wed, 27 Jan 2021 22:58:29 -0800 (PST) Received: from bj04616pcu01.spreadtrum.com ([117.18.48.82]) by smtp.gmail.com with ESMTPSA id y12sm4515750pfp.166.2021.01.27.22.58.06 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Jan 2021 22:58:28 -0800 (PST) From: Candle Sun To: keescook@chromium.org Cc: arnd@arndb.de, gregkh@linuxfoundation.org, natechancellor@gmail.com, ndesaulniers@google.com, candle.sun@unisoc.com, David.Laight@aculab.com, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: [PATCH v3] lkdtm: fix memory copy size for WRITE_KERN Date: Thu, 28 Jan 2021 14:57:39 +0800 Message-Id: <20210128065739.14124-1-candlesea@gmail.com> X-Mailer: git-send-email 2.17.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Candle Sun Though do_overwritten() follows do_nothing() in source code, the final memory address order is determined by the compiler. We can't always assume address of do_overwritten() is bigger than do_nothing(). At least the Clang we are using places do_overwritten() before do_nothing() in the object. This causes the copy size in lkdtm_WRITE_KERN() is *really* big and WRITE_KERN test on ARM32 arch will fail. Get absolute value of the address subtraction for memcpy() size. Signed-off-by: Candle Sun --- Changes in v3: - Clean some typo. - Remove one comment line. Changes in v2: - Use abs() in place of address comparison. --- drivers/misc/lkdtm/perms.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 2dede2ef658f..c9227e08f97f 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -31,13 +31,12 @@ static unsigned long ro_after_init __ro_after_init = 0x55AA5500; * This just returns to the caller. It is designed to be copied into * non-executable memory regions. */ -static void do_nothing(void) +static noinline void do_nothing(void) { return; } -/* Must immediately follow do_nothing for size calculuations to work out. */ -static void do_overwritten(void) +static noinline void do_overwritten(void) { pr_info("do_overwritten wasn't overwritten!\n"); return; @@ -113,7 +112,7 @@ void lkdtm_WRITE_KERN(void) size_t size; volatile unsigned char *ptr; - size = (unsigned long)do_overwritten - (unsigned long)do_nothing; + size = (size_t)abs((uintptr_t)do_overwritten - (uintptr_t)do_nothing); ptr = (unsigned char *)do_overwritten; pr_info("attempting bad %zu byte write at %px\n", size, ptr); -- 2.17.0