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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45A16C433F5 for ; Mon, 22 Nov 2021 11:23:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9DE316B0071; Mon, 22 Nov 2021 06:23:02 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 98CF16B0072; Mon, 22 Nov 2021 06:23:02 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 87C266B0073; Mon, 22 Nov 2021 06:23:02 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0210.hostedemail.com [216.40.44.210]) by kanga.kvack.org (Postfix) with ESMTP id 778606B0071 for ; Mon, 22 Nov 2021 06:23:02 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 40737181CC1B9 for ; Mon, 22 Nov 2021 11:22:52 +0000 (UTC) X-FDA: 78836328984.29.1D90525 Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) by imf16.hostedemail.com (Postfix) with ESMTP id 47398F000097 for ; Mon, 22 Nov 2021 11:22:48 +0000 (UTC) Received: (Authenticated sender: alex@ghiti.fr) by relay5-d.mail.gandi.net (Postfix) with ESMTPSA id 732BD1C000F; Mon, 22 Nov 2021 11:22:47 +0000 (UTC) Message-ID: <325663a5-d9a1-a8b8-7f16-c2985c319864@ghiti.fr> Date: Mon, 22 Nov 2021 12:22:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH 6/8] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT Content-Language: fr To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org References: From: Alex Ghiti In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 47398F000097 X-Stat-Signature: 54uqewup8m86877esx3g3stmhascc4un Authentication-Results: imf16.hostedemail.com; dkim=none; spf=none (imf16.hostedemail.com: domain of alex@ghiti.fr has no SPF policy when checking 217.70.183.197) smtp.mailfrom=alex@ghiti.fr; dmarc=none X-HE-Tag: 1637580168-51520 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: Hi Christophe, Le 22/11/2021 =C3=A0 09:48, Christophe Leroy a =C3=A9crit=C2=A0: > Commit e7142bf5d231 ("arm64, mm: make randomization selected by > generic topdown mmap layout") introduced a default version of > arch_randomize_brk() provided when > CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT is selected. >=20 > powerpc could select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT > but needs to provide its own arch_randomize_brk(). >=20 > In order to allow that, don't make > CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT select > CONFIG_ARCH_HAS_ELF_RANDOMIZE. Instead, ensure that > selecting CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and > selecting CONFIG_ARCH_HAS_ELF_RANDOMIZE has the same effect. This feels weird to me since if CONFIG_ARCH_HAS_ELF_RANDOMIZE is used=20 somewhere else at some point, it is not natural to add=20 CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT: can't we use a __weak=20 function or a new CONFIG_ARCH_HAS_RANDOMIZE_BRK? Thanks, Alex >=20 > Then only provide the default arch_randomize_brk() when the > architecture has not selected CONFIG_ARCH_HAS_ELF_RANDOMIZE. >=20 > Cc: Alexandre Ghiti > Signed-off-by: Christophe Leroy > --- > arch/Kconfig | 1 - > fs/binfmt_elf.c | 3 ++- > include/linux/elf-randomize.h | 3 ++- > mm/util.c | 2 ++ > 4 files changed, 6 insertions(+), 3 deletions(-) >=20 > diff --git a/arch/Kconfig b/arch/Kconfig > index 26b8ed11639d..ef3ce947b7a1 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -1000,7 +1000,6 @@ config HAVE_ARCH_COMPAT_MMAP_BASES > config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT > bool > depends on MMU > - select ARCH_HAS_ELF_RANDOMIZE > =20 > config HAVE_STACK_VALIDATION > bool > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index f8c7f26f1fbb..28968a189a91 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1287,7 +1287,8 @@ static int load_elf_binary(struct linux_binprm *b= prm) > * (since it grows up, and may collide early with the stack > * growing down), and into the unused ELF_ET_DYN_BASE region. > */ > - if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && > + if ((IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) || > + IS_ENABLED(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)) && > elf_ex->e_type =3D=3D ET_DYN && !interpreter) { > mm->brk =3D mm->start_brk =3D ELF_ET_DYN_BASE; > } > diff --git a/include/linux/elf-randomize.h b/include/linux/elf-randomiz= e.h > index da0dbb7b6be3..1e471ca7caaf 100644 > --- a/include/linux/elf-randomize.h > +++ b/include/linux/elf-randomize.h > @@ -4,7 +4,8 @@ > =20 > struct mm_struct; > =20 > -#ifndef CONFIG_ARCH_HAS_ELF_RANDOMIZE > +#if !defined(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && \ > + !defined(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT) > static inline unsigned long arch_mmap_rnd(void) { return 0; } > # if defined(arch_randomize_brk) && defined(CONFIG_COMPAT_BRK) > # define compat_brk_randomized > diff --git a/mm/util.c b/mm/util.c > index e58151a61255..edb9e94cceb5 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -344,6 +344,7 @@ unsigned long randomize_stack_top(unsigned long sta= ck_top) > } > =20 > #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT > +#ifndef CONFIG_ARCH_HAS_ELF_RANDOMIZE > unsigned long arch_randomize_brk(struct mm_struct *mm) > { > /* Is the current task 32bit ? */ > @@ -352,6 +353,7 @@ unsigned long arch_randomize_brk(struct mm_struct *= mm) > =20 > return randomize_page(mm->brk, SZ_1G); > } > +#endif > =20 > unsigned long arch_mmap_rnd(void) > { >=20