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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9FF07C433EF for ; Wed, 13 Oct 2021 12:45:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86645610FC for ; Wed, 13 Oct 2021 12:45:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234844AbhJMMrV (ORCPT ); Wed, 13 Oct 2021 08:47:21 -0400 Received: from pegase2.c-s.fr ([93.17.235.10]:60009 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234032AbhJMMrQ (ORCPT ); Wed, 13 Oct 2021 08:47:16 -0400 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HTsgq6Dhtz9sSZ; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id sJfMM_mh-Nz0; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4HTsgq5CtZz9sSP; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 9B4B48B77E; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id HiVledeU5Q_n; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) Received: from PO20335.IDSI0.si.c-s.fr (unknown [172.25.230.103]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 64F5C8B763; Wed, 13 Oct 2021 14:45:11 +0200 (CEST) Subject: Re: [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA() From: Christophe Leroy To: Kees Cook Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Andrew Morton , "James E.J. Bottomley" , Helge Deller , Arnd Bergmann , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org References: <7da92e59e148bd23564d63bdd8bcfaba0ba6d1f1.1633964380.git.christophe.leroy@csgroup.eu> <202110130018.7B2129375@keescook> <134b968f-f65f-cd74-3db1-fff60e5ebeb8@csgroup.eu> Message-ID: Date: Wed, 13 Oct 2021 14:45:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <134b968f-f65f-cd74-3db1-fff60e5ebeb8@csgroup.eu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr-FR Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 13/10/2021 à 09:48, Christophe Leroy a écrit : > > > Le 13/10/2021 à 09:39, Christophe Leroy a écrit : >> >> >> Le 13/10/2021 à 09:23, Kees Cook a écrit : >>> On Mon, Oct 11, 2021 at 05:25:36PM +0200, Christophe Leroy wrote: >>>> Behind a location, lkdtm_EXEC_RODATA() executes a real function, >>>> not a copy of do_nothing(). >>>> >>>> So do it directly instead of using execute_location(). >>>> >>>> And fix displayed addresses by dereferencing the function descriptors. >>>> >>>> Signed-off-by: Christophe Leroy >>>> --- >>>>   drivers/misc/lkdtm/perms.c | 9 ++++++++- >>>>   1 file changed, 8 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c >>>> index 442d60ed25ef..da16564e1ecd 100644 >>>> --- a/drivers/misc/lkdtm/perms.c >>>> +++ b/drivers/misc/lkdtm/perms.c >>>> @@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void) >>>> >>>>   void lkdtm_EXEC_RODATA(void) >>>>   { >>>> -    execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS); >>>> +    pr_info("attempting ok execution at %px\n", >>>> +        dereference_symbol_descriptor(do_nothing)); >>>> +    do_nothing(); >>>> + >>>> +    pr_info("attempting bad execution at %px\n", >>>> +        dereference_symbol_descriptor(lkdtm_rodata_do_nothing)); >>>> +    lkdtm_rodata_do_nothing(); >>>> +    pr_err("FAIL: func returned\n"); >>>>   } >>> >>> (In re-reading this more carefully, I see now why kallsyms.h is used >>> earlier: _function_ vs _symbol_ descriptor.) >>> >>> In the next patch: >>> >>> static noinline void execute_location(void *dst, bool write) >>> { >>> ... >>>         func = setup_function_descriptor(&fdesc, dst); >>>         if (IS_ERR(func)) >>>                 return; >>> >>>         pr_info("attempting bad execution at %px\n", dst); >>>         func(); >>>         pr_err("FAIL: func returned\n"); >>> } >>> >>> What are the conditions for which dereference_symbol_descriptor works >>> but dereference _function_descriptor doesn't? >>> >> >> When LKDTM is built as a module I guess ? >> > > To be more precise, dereference_symbol_descriptor() calls either > dereference_kernel_function_descriptor() or > dereference_module_function_descriptor() > > Both functions call dereference_function_descriptor() after checking > that we want to dereference something that is in the OPD section. > > If we call dereference_function_descriptor() directly instead of > dereference_symbol_descriptor() we skip the range verification and may > dereference something that is not a function descriptor. > > Should we do that ? > Indeed we are using it only for well known functions so using dereference_function_descriptor() is good enough. I'll use that in v2.