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 AC1CBC433FE for ; Wed, 13 Oct 2021 12:45:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 28FBF610F8 for ; Wed, 13 Oct 2021 12:45:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 28FBF610F8 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 B2B2F6B006C; Wed, 13 Oct 2021 08:45:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AB3E5900002; Wed, 13 Oct 2021 08:45:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 953FC6B0072; Wed, 13 Oct 2021 08:45:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0163.hostedemail.com [216.40.44.163]) by kanga.kvack.org (Postfix) with ESMTP id 813C36B006C for ; Wed, 13 Oct 2021 08:45:14 -0400 (EDT) Received: from smtpin38.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 3D9031840400F for ; Wed, 13 Oct 2021 12:45:14 +0000 (UTC) X-FDA: 78691384548.38.0CA7176 Received: from pegase2.c-s.fr (pegase2.c-s.fr [93.17.235.10]) by imf29.hostedemail.com (Postfix) with ESMTP id BC0E5900024B for ; Wed, 13 Oct 2021 12:45:13 +0000 (UTC) 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 Authentication-Results: imf29.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf29.hostedemail.com: domain of christophe.leroy@csgroup.eu designates 93.17.235.10 as permitted sender) smtp.mailfrom=christophe.leroy@csgroup.eu X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BC0E5900024B X-Stat-Signature: b3geujby4gwcczdkdbrbpni78x1ibpwk X-HE-Tag: 1634129113-467842 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 09:48, Christophe Leroy a =C3=A9crit=C2=A0: >=20 >=20 > Le 13/10/2021 =C3=A0 09:39, Christophe Leroy a =C3=A9crit=C2=A0: >> >> >> 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 descriptor= s. >>>> >>>> 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_A= S_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_descr= iptor(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_descr= iptor(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_de= scriptor(&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 ex= ecution 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 returne= d\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 ? >> >=20 > To be more precise, dereference_symbol_descriptor() calls either=20 > dereference_kernel_function_descriptor() or=20 > dereference_module_function_descriptor() >=20 > Both functions call dereference_function_descriptor() after checking=20 > that we want to dereference something that is in the OPD section. >=20 > 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. >=20 > Should we do that ? >=20 Indeed we are using it only for well known functions so using=20 dereference_function_descriptor() is good enough. I'll use that in v2.