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=-18.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 07B9AC43470 for ; Thu, 13 May 2021 22:33:09 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 C1C8761354 for ; Thu, 13 May 2021 22:33:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C1C8761354 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.127091.238774 (Exim 4.92) (envelope-from ) id 1lhJsy-0006Tu-GB; Thu, 13 May 2021 22:32:52 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 127091.238774; Thu, 13 May 2021 22:32:52 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhJsy-0006Tn-DL; Thu, 13 May 2021 22:32:52 +0000 Received: by outflank-mailman (input) for mailman id 127091; Thu, 13 May 2021 22:32:51 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lhJsx-0006Th-RB for xen-devel@lists.xenproject.org; Thu, 13 May 2021 22:32:51 +0000 Received: from mail.kernel.org (unknown [198.145.29.99]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 77993eda-fc7d-41be-87b8-1cc155dd68d9; Thu, 13 May 2021 22:32:51 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 093ED61354; Thu, 13 May 2021 22:32:49 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 77993eda-fc7d-41be-87b8-1cc155dd68d9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620945170; bh=JobBn5ClyiCaU5MqM2+6SS0+A3r7udsmTCc7WW9sszU=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=eL477i+/7fLUyGfUrES/7dhqEaGnmpYfxoLW9aDL7PTPqT/p5jMLMuGGe1XK6+J7a nsxOJGtXF/wW1OKHHE3BQNtnc7tTGRNsRjlURbaXYhoOjQngTzT1u69457lMNVNu9D 70aaF2Ii7OktVIzxxKDTto0YYOE/bKURD1xXueDVMmaHNEZJH9k6O5g/i9FMoxwCj6 hVRDgnW+LIZh5F5LwDhairfgeClxC+EKzqCf/wWL4VIQEi99FAww/Jg0CQyPVh0lgI WMqw8qf9Wy/TAAziRJJoajTD59DwTsx2+lNayTqLu8KRP5iC+Pt7swI3KFpP9JtxUx 7FVreKHG4EvnA== Date: Thu, 13 May 2021 15:32:49 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Julien Grall cc: Stefano Stabellini , xen-devel@lists.xenproject.org, Wei.Chen@arm.com, Henry.Wang@arm.com, Penny.Zheng@arm.com, Bertrand.Marquis@arm.com, Julien Grall , Volodymyr Babchuk Subject: Re: [PATCH RFCv2 08/15] xen/arm32: mm: Check if the virtual address is shared before updating it In-Reply-To: Message-ID: References: <20210425201318.15447-1-julien@xen.org> <20210425201318.15447-9-julien@xen.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Wed, 12 May 2021, Julien Grall wrote: > Hi Stefano, > > On 12/05/2021 23:00, Stefano Stabellini wrote: > > On Sun, 25 Apr 2021, Julien Grall wrote: > > > From: Julien Grall > > > > > > Only the first 2GB of the virtual address space is shared between all > > > the page-tables on Arm32. > > > > > > There is a long outstanding TODO in xen_pt_update() stating that the > > > function is can only work with shared mapping. Nobody has ever called > > ^ remove > > > > > the function with private mapping, however as we add more callers > > > there is a risk to mess things up. > > > > > > Introduce a new define to mark the ened of the shared mappings and use > > ^end > > > > > it in xen_pt_update() to verify if the address is correct. > > > > > > Note that on Arm64, all the mappings are shared. Some compiler may > > > complain about an always true check, so the new define is not introduced > > > for arm64 and the code is protected with an #ifdef. > > On arm64 we could maybe define SHARED_VIRT_END to an arbitrarely large > > value, such as: > > > > #define SHARED_VIRT_END (1UL<<48) > > > > or: > > > > #define SHARED_VIRT_END DIRECTMAP_VIRT_END > > > > ? > > I thought about it but I didn't want to define to a random value... I felt not > define it was better. Yeah, I see your point: any restrictions in addressing (e.g. 48bits) are physical address restrictions. Here we are talking about virtual address restriction, and I don't think there are actually any restrictions there? We could validly map something at 0xffff_ffff_ffff_ffff. So even (1<<48) which makes sense at the physical level, doesn't make sense in terms of virtual addresses. > > > Signed-off-by: Julien Grall > > > > > > --- > > > Changes in v2: > > > - New patch > > > --- > > > xen/arch/arm/mm.c | 11 +++++++++-- > > > xen/include/asm-arm/config.h | 4 ++++ > > > 2 files changed, 13 insertions(+), 2 deletions(-) > > > > > > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c > > > index 8fac24d80086..5c17cafff847 100644 > > > --- a/xen/arch/arm/mm.c > > > +++ b/xen/arch/arm/mm.c > > > @@ -1275,11 +1275,18 @@ static int xen_pt_update(unsigned long virt, > > > * For arm32, page-tables are different on each CPUs. Yet, they > > > share > > > * some common mappings. It is assumed that only common mappings > > > * will be modified with this function. > > > - * > > > - * XXX: Add a check. > > > */ > > > const mfn_t root = virt_to_mfn(THIS_CPU_PGTABLE); > > > +#ifdef SHARED_VIRT_END > > > + if ( virt > SHARED_VIRT_END || > > > + (SHARED_VIRT_END - virt) < nr_mfns ) > > > > The following would be sufficient, right? > > > > if ( virt + nr_mfns > SHARED_VIRT_END ) > > This would not protect against an overflow. So I think it is best if we keep > my version. But there can be no overflow with the way SHARED_VIRT_END is defined. Even if SHARED_VIRT_END was defined at (1<<48) there can be no overflow. Only if we defined SHARED_VIRT_END as 0xffff_ffff_ffff_ffff we would have an overflow, but you wrote above that your preference is not to do that.