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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16545C7618B for ; Fri, 26 Jul 2019 11:48:37 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DD8A3229F3 for ; Fri, 26 Jul 2019 11:48:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="NnCMGFvU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD8A3229F3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ghiti.fr Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=KA+kmMJQuVs1KKPRNXyX0WyCtq+Vyfamllka9C9rv/I=; b=NnCMGFvUtGcd1WX4/Wjk7GqSL P/9b5LGq1NqcqM9XLisgEMKoRJdip1YvhcxVgsRlHQiDsL1LIcAcTs2cvLP5v0/AbnD8YiRIQSEwk feh8SCwd44tK8KLZnUmrwB8LA7eij01etwYW2RIVNd4sIS4M1s7nM3M0g+SlA/4IJZJlShbQPT2nG bO/hH9poRJux3v/Wv+Uz4NtlGhg6U30owYjUpW5/YlMXl3t/rpo84M52rH/5GdRfChZ0IGrNFxst5 Nq5d/Hw3PtqyImKXTA6g/Wh3z0wgDQzbvgwsjN3vu8LEX/JhROsViYXU561k3cGnMpTsoq3VfN8/g pB9d58hkA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hqyiC-0003pX-BZ; Fri, 26 Jul 2019 11:48:36 +0000 Received: from relay8-d.mail.gandi.net ([217.70.183.201]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hqyi8-0003nY-71; Fri, 26 Jul 2019 11:48:34 +0000 X-Originating-IP: 81.250.144.103 Received: from [10.30.1.20] (lneuilly-657-1-5-103.w81-250.abo.wanadoo.fr [81.250.144.103]) (Authenticated sender: alex@ghiti.fr) by relay8-d.mail.gandi.net (Postfix) with ESMTPSA id 3CAE81BF207; Fri, 26 Jul 2019 11:48:08 +0000 (UTC) Subject: Re: [PATCH REBASE v4 14/14] riscv: Make mmap allocation top-down by default To: Paul Walmsley References: <20190724055850.6232-1-alex@ghiti.fr> <20190724055850.6232-15-alex@ghiti.fr> From: Alexandre Ghiti Message-ID: <6b2b45a5-0ac4-db73-8f50-ab182a0cb621@ghiti.fr> Date: Fri, 26 Jul 2019 13:48:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Language: fr X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190726_044832_564133_5B03736B X-CRM114-Status: GOOD ( 20.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Albert Ou , Kees Cook , Catalin Marinas , Daniel Cashman , Palmer Dabbelt , Will Deacon , Russell King , Ralf Baechle , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Paul Burton , linux-riscv@lists.infradead.org, Alexander Viro , James Hogan , linux-fsdevel@vger.kernel.org, Andrew Morton , linux-mips@vger.kernel.org, Christoph Hellwig , linux-arm-kernel@lists.infradead.org, Luis Chamberlain Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/26/19 2:20 AM, Paul Walmsley wrote: > Hi Alexandre, > > I have a few questions about this patch. Sorry to be dense here ... > > On Wed, 24 Jul 2019, Alexandre Ghiti wrote: > >> In order to avoid wasting user address space by using bottom-up mmap >> allocation scheme, prefer top-down scheme when possible. >> >> Before: >> root@qemuriscv64:~# cat /proc/self/maps >> 00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils >> 00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils >> 00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils >> 00018000-00039000 rw-p 00000000 00:00 0 [heap] >> 1555556000-155556d000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so >> 155556d000-155556e000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so >> 155556e000-155556f000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so >> 155556f000-1555570000 rw-p 00000000 00:00 0 >> 1555570000-1555572000 r-xp 00000000 00:00 0 [vdso] >> 1555574000-1555576000 rw-p 00000000 00:00 0 >> 1555576000-1555674000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so >> 1555674000-1555678000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so >> 1555678000-155567a000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so >> 155567a000-15556a0000 rw-p 00000000 00:00 0 >> 3fffb90000-3fffbb1000 rw-p 00000000 00:00 0 [stack] >> >> After: >> root@qemuriscv64:~# cat /proc/self/maps >> 00010000-00016000 r-xp 00000000 fe:00 6389 /bin/cat.coreutils >> 00016000-00017000 r--p 00005000 fe:00 6389 /bin/cat.coreutils >> 00017000-00018000 rw-p 00006000 fe:00 6389 /bin/cat.coreutils >> 2de81000-2dea2000 rw-p 00000000 00:00 0 [heap] >> 3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0 >> 3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187 /lib/libc-2.28.so >> 3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187 /lib/libc-2.28.so >> 3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187 /lib/libc-2.28.so >> 3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0 >> 3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0 [vdso] >> 3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193 /lib/ld-2.28.so >> 3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193 /lib/ld-2.28.so >> 3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193 /lib/ld-2.28.so >> 3ff7fff000-3ff8000000 rw-p 00000000 00:00 0 >> 3fff888000-3fff8a9000 rw-p 00000000 00:00 0 [stack] >> >> Signed-off-by: Alexandre Ghiti >> Reviewed-by: Christoph Hellwig >> Reviewed-by: Kees Cook >> --- >> arch/riscv/Kconfig | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig >> index 59a4727ecd6c..6a63973873fd 100644 >> --- a/arch/riscv/Kconfig >> +++ b/arch/riscv/Kconfig >> @@ -54,6 +54,17 @@ config RISCV >> select EDAC_SUPPORT >> select ARCH_HAS_GIGANTIC_PAGE >> select ARCH_WANT_HUGE_PMD_SHARE if 64BIT >> + select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU >> + select HAVE_ARCH_MMAP_RND_BITS >> + >> +config ARCH_MMAP_RND_BITS_MIN >> + default 18 > Could you help me understand the rationale behind this constant? Indeed, I took that from arm64 code and I did not think enough about it: that's great you spotted this because that's a way too large value for 32 bits as it would, at minimum, make mmap random offset go up to 1GB (18 + 12), which is a big hole for this small address space :) arm and mips propose 8 as default value for 32bits systems which is 1MB offset at minimum. > >> + >> +# max bits determined by the following formula: >> +# VA_BITS - PAGE_SHIFT - 3 > I realize that these lines are probably copied from arch/arm64/Kconfig. > But the rationale behind the "- 3" is not immediately obvious. This > apparently originates from commit 8f0d3aa9de57 ("arm64: mm: support > ARCH_MMAP_RND_BITS"). Can you provide any additional context here? The formula comes from commit d07e22597d1d ("mm: mmap: add new /proc tunable for mmap_base ASLR"), where the author states that "generally a 3-4 bits less than the number of bits in the user-space accessible virtual address space [allows to] give the greatest flexibility without generating an invalid mmap_base address". In practice, that limits the mmap random offset to at maximum 1/8 (for - 3) of the total address space. > >> +config ARCH_MMAP_RND_BITS_MAX >> + default 33 if 64BIT # SV48 based > The rationale here is clear for Sv48, per the above formula: > > (48 - 12 - 3) = 33 > >> + default 18 > However, here it is less clear to me. For Sv39, shouldn't this be > > (39 - 12 - 3) = 24 > > ? And what about Sv32? You're right. Is there a way to distinguish between sv39 and sv48 here ? Thanks Paul, Alex > > > - Paul > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel