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 B08ECC433E0 for ; Mon, 25 Jan 2021 09:51:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5134322C9C for ; Mon, 25 Jan 2021 09:51:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727212AbhAYJuN (ORCPT ); Mon, 25 Jan 2021 04:50:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37580 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726635AbhAYJfw (ORCPT ); Mon, 25 Jan 2021 04:35:52 -0500 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1260BC061224 for ; Mon, 25 Jan 2021 00:56:38 -0800 (PST) Received: by mail-pl1-x636.google.com with SMTP id r4so7156944pls.11 for ; Mon, 25 Jan 2021 00:56:38 -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=0Tg3AO11+laABwQxj64s25+YkKlIw2DDqPTzk+9m3NA=; b=WoCye80M8x4ZKxCAmP00jU6mS+f/VayYVmmikRShox5xNBLkJ/hSaVzDTzCbGdp9s4 pVbQEeNUb0I2B+CYEnmt/Yt6BRIOnzgz2CEgGocb79uG+XmUiZ2Zzf9hZ54fNCZeRBOS pwCKPuf36lXbZ+2jg4FaOOAQJbTESr5CKLSIjtm2dNM0qsMH+n5jx5w/knWfmo0Nftdv OAMM6tvUM+TIytMcE74rnk6fbE5smQJniMc6AwCWPD2sXpbZBsFtKEDcU+ifRchZJg26 E/oybp+PF/LNzIe1iHTz1flFkDCIrzm6/ltdFGbrsSHh2RYWqy8mO22yArN9KGqlitH1 7E+g== 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=0Tg3AO11+laABwQxj64s25+YkKlIw2DDqPTzk+9m3NA=; b=MyAg2Scj3hLfaQu8t4nsdzaXjt4n+luLM2VOxGrWSQHYuAff23J4274xqSIFqTlVVr kwcL5Q5b/ti3sYUwFmAbl3oMykWaKwkLXYApOrZiwSlIJvZnFBRBny9CM/3ORYjhxpuV AmMxiMKptLmeUXA13jfQ8iYQcKnuMsv44gvn1zNJqwsWNh9rZ87FlNHt9oz1c7lSNDcM Hhy+3HCmZBzB2JnHrbbxzNuo9kb/4kttoGIX2CjKtkCNFtohHPW9zze6eTAchAvMc0Hc WCduw4dsicbQxU1n+oFynulgpOVauJ0WfjmzL7iyH4OqJi/L+rnVMW8p5QBuTidr4mKg P2RQ== X-Gm-Message-State: AOAM530NjcavAuvrdzIav3mkWr8cfs7n1GD/3NxmspMYoNNIo41EToWs KteaP8vSC+sqKAgaP7uQMRg= X-Google-Smtp-Source: ABdhPJyK64XWDJ4pEFtiZoiBJZthYUHFUTOaLkdd9WQt0tQ2FDjvYPOByicZMyWxv2jgwF+BqOR3pQ== X-Received: by 2002:a17:902:bd01:b029:da:3d4f:abe1 with SMTP id p1-20020a170902bd01b02900da3d4fabe1mr18912704pls.16.1611564997676; Mon, 25 Jan 2021 00:56:37 -0800 (PST) Received: from bj04616pcu01.spreadtrum.com ([117.18.48.82]) by smtp.gmail.com with ESMTPSA id m18sm12918724pfd.206.2021.01.25.00.56.35 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Jan 2021 00:56:37 -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, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: [PATCH] lkdtm: fix memory copy size for WRITE_KERN Date: Mon, 25 Jan 2021 16:56:22 +0800 Message-Id: <20210125085622.2322-1-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 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. Compare the address order before doing the subtraction. Signed-off-by: Candle Sun --- drivers/misc/lkdtm/perms.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 2dede2ef658f..fbfbdf89d668 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -31,13 +31,13 @@ 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; @@ -110,15 +110,14 @@ void lkdtm_WRITE_RO_AFTER_INIT(void) void lkdtm_WRITE_KERN(void) { - size_t size; - volatile unsigned char *ptr; + unsigned long value_dow = (unsigned long)do_overwritten; + unsigned long value_do = (unsigned long)do_nothing; + size_t size = (size_t)(value_dow > value_do ? + value_dow - value_do : value_do - value_dow); - size = (unsigned long)do_overwritten - (unsigned long)do_nothing; - ptr = (unsigned char *)do_overwritten; - - pr_info("attempting bad %zu byte write at %px\n", size, ptr); - memcpy((void *)ptr, (unsigned char *)do_nothing, size); - flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size)); + pr_info("attempting bad %zu byte write at %px\n", size, do_overwritten); + memcpy((void *)value_dow, (void *)value_do, size); + flush_icache_range(value_dow, value_dow + (unsigned long)size); pr_err("FAIL: survived bad write\n"); do_overwritten(); -- 2.17.0