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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id BF645C433F5 for ; Mon, 22 Nov 2021 11:47:49 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HyQW806Jmz3c6t for ; Mon, 22 Nov 2021 22:47:48 +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) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HyQVb01xDz2xRp for ; Mon, 22 Nov 2021 22:47:16 +1100 (AEDT) Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4HyQVT4f10z9sSk; Mon, 22 Nov 2021 12:47:13 +0100 (CET) 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 YkgrPNJYfsxj; Mon, 22 Nov 2021 12:47:13 +0100 (CET) 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 4HyQVT3h2Rz9sSZ; Mon, 22 Nov 2021 12:47:13 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 662C68B774; Mon, 22 Nov 2021 12:47:13 +0100 (CET) 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 fbOL2ToGz7tZ; Mon, 22 Nov 2021 12:47:13 +0100 (CET) Received: from [172.25.230.108] (unknown [172.25.230.108]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 20B3A8B765; Mon, 22 Nov 2021 12:47:13 +0100 (CET) Message-ID: <2dd4a22e-f1a5-683c-2d17-ce726f03f4c5@csgroup.eu> Date: Mon, 22 Nov 2021 12:47:13 +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-FR To: Alex Ghiti , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman References: <325663a5-d9a1-a8b8-7f16-c2985c319864@ghiti.fr> From: Christophe Leroy In-Reply-To: <325663a5-d9a1-a8b8-7f16-c2985c319864@ghiti.fr> Content-Type: text/plain; charset=UTF-8; format=flowed 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-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 22/11/2021 à 12:22, Alex Ghiti a écrit : > Hi Christophe, > > Le 22/11/2021 à 09:48, Christophe Leroy a écrit : >> 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 > somewhere else at some point, it is not natural to add > CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT: can't we use a __weak > 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 it be from CONFIG_ARCH_HAS_ELF_RANDOMIZE ? In fact I find it weird that CONFIG_ARCH_HAS_ELF_RANDOMIZE is selected by CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and not by the arch itself. On the other hand CONFIG_ARCH_HAS_ELF_RANDOMIZE also handles arch_mmap_rnd() and here we are talking about arch_randomize_brk() only. In the begining I was thinking about adding a CONFIG_ARCH_WANT_DEFAULT_RANDOMIZE_BRK, but it was meaning adding it to the few other arches selecting CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT. So I think I will go for the __weak function option. Thanks Christophe