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 DAD5CC433F5 for ; Mon, 22 Nov 2021 12:58:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4B7DC6B0071; Mon, 22 Nov 2021 07:58:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 467B66B0072; Mon, 22 Nov 2021 07:58:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 32FDD6B0073; Mon, 22 Nov 2021 07:58:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0221.hostedemail.com [216.40.44.221]) by kanga.kvack.org (Postfix) with ESMTP id 24CAA6B0071 for ; Mon, 22 Nov 2021 07:58:14 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id D5B768A9A2 for ; Mon, 22 Nov 2021 12:58:03 +0000 (UTC) X-FDA: 78836568888.29.8BC9F65 Received: from relay1-d.mail.gandi.net (relay1-d.mail.gandi.net [217.70.183.193]) by imf29.hostedemail.com (Postfix) with ESMTP id E500D9001A92 for ; Mon, 22 Nov 2021 12:58:00 +0000 (UTC) Received: (Authenticated sender: alex@ghiti.fr) by relay1-d.mail.gandi.net (Postfix) with ESMTPSA id F15E724001C; Mon, 22 Nov 2021 12:57:56 +0000 (UTC) Message-ID: Date: Mon, 22 Nov 2021 13:57:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1 Subject: Re: [PATCH 6/8] mm: Allow arch specific arch_randomize_brk() with CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT Content-Language: en-US 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: <325663a5-d9a1-a8b8-7f16-c2985c319864@ghiti.fr> <2dd4a22e-f1a5-683c-2d17-ce726f03f4c5@csgroup.eu> From: Alexandre ghiti In-Reply-To: <2dd4a22e-f1a5-683c-2d17-ce726f03f4c5@csgroup.eu> Content-Type: text/plain; charset=UTF-8; format=flowed X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: E500D9001A92 X-Stat-Signature: 1izfgwisiowzb91kq8kykaaczc3mp86r Authentication-Results: imf29.hostedemail.com; dkim=none; spf=none (imf29.hostedemail.com: domain of alex@ghiti.fr has no SPF policy when checking 217.70.183.193) smtp.mailfrom=alex@ghiti.fr; dmarc=none X-HE-Tag: 1637585880-362369 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000020, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11/22/21 12:47, Christophe Leroy wrote: > > > Le 22/11/2021 =C3=A0 12:22, Alex Ghiti a =C3=A9crit=C2=A0: >> 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. >>> >>> powerpc could select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT >>> but needs to provide its own arch_randomize_brk(). >>> >>> 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? > > > Yes I also found things a bit weird. > > CONFIG_ARCH_HAS_RANDOMIZE_BRK could be an idea but how different would=20 > it be from CONFIG_ARCH_HAS_ELF_RANDOMIZE ? In fact I find it weird=20 > that CONFIG_ARCH_HAS_ELF_RANDOMIZE is selected by=20 > CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and not by the arch itself= . IIRC, this was a request from Kees Cook who wanted to enforce this=20 security measure. > > On the other hand CONFIG_ARCH_HAS_ELF_RANDOMIZE also handles=20 > arch_mmap_rnd() and here we are talking about arch_randomize_brk() only= . > > In the begining I was thinking about adding a=20 > CONFIG_ARCH_WANT_DEFAULT_RANDOMIZE_BRK, but it was meaning adding it=20 > to the few other arches selecting=20 > CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT. > > So I think I will go for the __weak function option. Ok, thanks. Alex > > Thanks > Christophe