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 E680FC433EF for ; Wed, 13 Oct 2021 07:49:28 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 68D7260E96 for ; Wed, 13 Oct 2021 07:49:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 68D7260E96 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HTl6b0zPmz304t for ; Wed, 13 Oct 2021 18:49:27 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.235.10; helo=pegase2.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Received: from pegase2.c-s.fr (pegase2.c-s.fr [93.17.235.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HTl645TYyz2yWn for ; Wed, 13 Oct 2021 18:48:59 +1100 (AEDT) Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HTl5z2pvVz9sSS; Wed, 13 Oct 2021 09:48:55 +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 adj2QVTuN7-k; Wed, 13 Oct 2021 09:48:55 +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 4HTl5z1lNGz9sRn; Wed, 13 Oct 2021 09:48:55 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 2425B8B77E; Wed, 13 Oct 2021 09:48:55 +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 m9ol1goCz6oD; Wed, 13 Oct 2021 09:48:55 +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 E7EB88B763; Wed, 13 Oct 2021 09:48:54 +0200 (CEST) Subject: Re: [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA() From: Christophe Leroy To: Kees Cook References: <7da92e59e148bd23564d63bdd8bcfaba0ba6d1f1.1633964380.git.christophe.leroy@csgroup.eu> <202110130018.7B2129375@keescook> Message-ID: <134b968f-f65f-cd74-3db1-fff60e5ebeb8@csgroup.eu> Date: Wed, 13 Oct 2021 09:48:54 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr-FR Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Arnd Bergmann , Greg Kroah-Hartman , Helge Deller , linux-kernel@vger.kernel.org, "James E.J. Bottomley" , linux-mm@kvack.org, Paul Mackerras , Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 ? Christophe