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 27CB6C433EF for ; Wed, 13 Oct 2021 07:39:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1121461053 for ; Wed, 13 Oct 2021 07:39:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238565AbhJMHlk (ORCPT ); Wed, 13 Oct 2021 03:41:40 -0400 Received: from pegase2.c-s.fr ([93.17.235.10]:44963 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238509AbhJMHlj (ORCPT ); Wed, 13 Oct 2021 03:41:39 -0400 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HTkvC3NdVz9sSS; Wed, 13 Oct 2021 09:39:35 +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 7TkwAiuNfAn6; Wed, 13 Oct 2021 09:39:35 +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 4HTkvC2VHFz9sRn; Wed, 13 Oct 2021 09:39:35 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 3D8048B77E; Wed, 13 Oct 2021 09:39:35 +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 Hl8eIAk3DFNP; Wed, 13 Oct 2021 09:39:35 +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 104368B763; Wed, 13 Oct 2021 09:39:35 +0200 (CEST) Subject: Re: [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA() 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> From: Christophe Leroy Message-ID: Date: Wed, 13 Oct 2021 09:39:34 +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: <202110130018.7B2129375@keescook> 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-arch@vger.kernel.org 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 ? Christophe