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=-12.7 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 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 8AB95C433E0 for ; Tue, 26 Jan 2021 14:19:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4709022B51 for ; Tue, 26 Jan 2021 14:19:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405801AbhAZOSy (ORCPT ); Tue, 26 Jan 2021 09:18:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42828 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405679AbhAZOSR (ORCPT ); Tue, 26 Jan 2021 09:18:17 -0500 Received: from mail-yb1-xb29.google.com (mail-yb1-xb29.google.com [IPv6:2607:f8b0:4864:20::b29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8ABC3C0611C2 for ; Tue, 26 Jan 2021 06:17:37 -0800 (PST) Received: by mail-yb1-xb29.google.com with SMTP id e67so16827243ybc.12 for ; Tue, 26 Jan 2021 06:17:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AS/PqSCLXPUX5/0cv/D32Ab1nbbd5GInwJYzei8iock=; b=HGnNuROYaN8L9CsOXEklj4GmusrUZy6n73qQEoZo2Sjy2TFTiAvJmIExJ0APhd9MYX yGaoOrlz0ow32/0hUv4+6PfdcmJRqVbactaa2ErQ8QOr5RGgoKJiDldaSyJeBrhCFdq2 SrzM1lK1c/gdOVScVkBHIqD2u2iuJmUQMGGRHuuUIglDfb0TjdG+rFDsiVcgkBAbMdyg 2z8edNrPGdqGmuC0SXgBfV2mAK3D7NbSg2DEYn05/MeVsd6WPRC31KfxGZC2Kps/gAik i4eD8yHR7/ztWDbd68YXNld8737gL6+mhdQrAy3y7pec0b75b7IwV2BkriDFmSlCxAbV lnmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AS/PqSCLXPUX5/0cv/D32Ab1nbbd5GInwJYzei8iock=; b=ITcInCmoyWOdCZWbCPTU3W4ZxpYq/uhKn6sD22T2/6ovbk6w724iiiM1AMg6lyejnr 2gABcVqszdxfJkVm4E5CWPmpUTokiKZpy4GGTz1pk0YYrQ3OKMAcYQ4PuBLBqTR5i1a9 N9WXNEI6wPbCfHp/upqLdU8+m+ihYrycoTmOrmuh0v1bLDEArRMYKlUBQj+CalgwPfAW xJnh7odjNptYnDI6lV0u+Mvq64z7fqzFe0lomPuz0ZmfRdcKnzA7t3Cyhs78uY/W8YzA eNobe5qDphw421Kk/2UikZbRM4dx946XEnxH3p5nhZYLl3osVEduGUrRYnfSDOfxJIRc AVIA== X-Gm-Message-State: AOAM531zNKX/hmR1NYcB6xpIoOGsquaaqPYbUgsVd35gKoYti3ynTCiz qiKY6x4YPFF8Sn4bY1+WzI38YRZvAsYY7/yWHhk= X-Google-Smtp-Source: ABdhPJwa4WaRWJZ2FL9jNUSCsccppk1hf32g/uV+OeB6mucj3lPd8nqW407fBdUXGu16INj7DAX/rk8+FX6WwEC4QRk= X-Received: by 2002:a25:2a56:: with SMTP id q83mr8430303ybq.144.1611670656827; Tue, 26 Jan 2021 06:17:36 -0800 (PST) MIME-Version: 1.0 References: <20210125085622.2322-1-candlesea@gmail.com> In-Reply-To: From: Candle Sun Date: Tue, 26 Jan 2021 22:17:25 +0800 Message-ID: Subject: Re: [PATCH] lkdtm: fix memory copy size for WRITE_KERN To: Nick Desaulniers Cc: Kees Cook , Arnd Bergmann , Greg KH , Nathan Chancellor , Candle Sun , LKML , clang-built-linux Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 26, 2021 at 5:16 AM Nick Desaulniers wrote: > > On Mon, Jan 25, 2021 at 12:56 AM Candle Sun wrote: > > > > 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; > > Thanks for the patch! Might it be simpler to do: > > size = abs((uintptr_t)do_overwritten - (uintptr_t)do_nothing)); > > Then I don't think much of this function needs to be changed. > Thanks Nick. abs() is better, I will check the patch. Regards, Candle > > - 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 > > > > > -- > Thanks, > ~Nick Desaulniers