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 5EC82C433EF for ; Wed, 13 Oct 2021 07:48:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0C2C160E96 for ; Wed, 13 Oct 2021 07:48:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0C2C160E96 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id A0804940010; Wed, 13 Oct 2021 03:48:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9914A940007; Wed, 13 Oct 2021 03:48:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8807F940010; Wed, 13 Oct 2021 03:48:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0160.hostedemail.com [216.40.44.160]) by kanga.kvack.org (Postfix) with ESMTP id 78987940007 for ; Wed, 13 Oct 2021 03:48:57 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 30E3118239AAA for ; Wed, 13 Oct 2021 07:48:57 +0000 (UTC) X-FDA: 78690637914.18.494C6C6 Received: from pegase2.c-s.fr (pegase2.c-s.fr [93.17.235.10]) by imf02.hostedemail.com (Postfix) with ESMTP id D108F7001A0A for ; Wed, 13 Oct 2021 07:48:56 +0000 (UTC) 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 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> 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 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D108F7001A0A X-Stat-Signature: 1yztrqsyfq16p53peog3ykbnqe6bowft Authentication-Results: imf02.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf02.hostedemail.com: domain of christophe.leroy@csgroup.eu designates 93.17.235.10 as permitted sender) smtp.mailfrom=christophe.leroy@csgroup.eu X-HE-Tag: 1634111336-793287 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 13/10/2021 =C3=A0 09:39, Christophe Leroy a =C3=A9crit=C2=A0: >=20 >=20 > Le 13/10/2021 =C3=A0 09:23, Kees Cook a =C3=A9crit=C2=A0: >> 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 >>> --- >>> =C2=A0 drivers/misc/lkdtm/perms.c | 9 ++++++++- >>> =C2=A0 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) >>> >>> =C2=A0 void lkdtm_EXEC_RODATA(void) >>> =C2=A0 { >>> -=C2=A0=C2=A0=C2=A0 execute_location(lkdtm_rodata_do_nothing, CODE_AS= _IS); >>> +=C2=A0=C2=A0=C2=A0 pr_info("attempting ok execution at %px\n", >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 dereference_symbol_descri= ptor(do_nothing)); >>> +=C2=A0=C2=A0=C2=A0 do_nothing(); >>> + >>> +=C2=A0=C2=A0=C2=A0 pr_info("attempting bad execution at %px\n", >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 dereference_symbol_descri= ptor(lkdtm_rodata_do_nothing)); >>> +=C2=A0=C2=A0=C2=A0 lkdtm_rodata_do_nothing(); >>> +=C2=A0=C2=A0=C2=A0 pr_err("FAIL: func returned\n"); >>> =C2=A0 } >> >> (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) >> { >> ... >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 func =3D setup_function_des= criptor(&fdesc, dst); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (IS_ERR(func)) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 return; >> >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pr_info("attempting bad exe= cution at %px\n", dst); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 func(); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pr_err("FAIL: func returned= \n"); >> } >> >> What are the conditions for which dereference_symbol_descriptor works >> but dereference _function_descriptor doesn't? >> >=20 > When LKDTM is built as a module I guess ? >=20 To be more precise, dereference_symbol_descriptor() calls either=20 dereference_kernel_function_descriptor() or=20 dereference_module_function_descriptor() Both functions call dereference_function_descriptor() after checking=20 that we want to dereference something that is in the OPD section. If we call dereference_function_descriptor() directly instead of=20 dereference_symbol_descriptor() we skip the range verification and may=20 dereference something that is not a function descriptor. Should we do that ? Christophe