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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E53CC433F5 for ; Wed, 19 Jan 2022 22:39:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357567AbiASWjB (ORCPT ); Wed, 19 Jan 2022 17:39:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44028 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243245AbiASWi7 (ORCPT ); Wed, 19 Jan 2022 17:38:59 -0500 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7843C061574 for ; Wed, 19 Jan 2022 14:38:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=RZdMRmyvk76b5yPhRV2i+xX8UdR7XO+5UD90vqV4ELA=; b=dFvz8pXyCLGzxAuQ7QKau+I68U HqsQzZKmn0yL/Q/2FyQvN1ZGs8jxyGsd/vXe++hc+4GVVXKGIaeAl4K2c9M6eIxIqgbLOyyReENKu MiTNbb+83iz0oBPL99bdZa7zLJBKfhb/3CFOibP81z07+uQknIT3fFnJftf8tHg9sQsipUD2VvbPR rvsjdEgZZE+btlgnVhXphSBlOmMNvsN3o4eew2G3YGLtFdB+FIhgBPwtJu4+h1Njj0fjJUXlciUO9 4HmveomFLZs7gQFgmIKkZ92exDbwUPyzLQtJvsVtV/KYVJGAp3kWtGaS5ghRkCW9KCuMVi7h93g0I 72ZF+mSw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:56790) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nAJbM-0005Ax-DK; Wed, 19 Jan 2022 22:38:48 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1nAJbG-0005cr-TZ; Wed, 19 Jan 2022 22:38:42 +0000 Date: Wed, 19 Jan 2022 22:38:42 +0000 From: "Russell King (Oracle)" To: Matthew Wilcox Cc: Robin Murphy , Yury Norov , Catalin Marinas , Will Deacon , Andrew Morton , Nicholas Piggin , Ding Tianhong , Anshuman Khandual , Alexey Klimov , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] vmap(): don't allow invalid pages Message-ID: References: <20220118235244.540103-1-yury.norov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 19, 2022 at 07:35:33PM +0000, Matthew Wilcox wrote: > On Wed, Jan 19, 2022 at 06:57:34PM +0000, Russell King (Oracle) wrote: > > On Wed, Jan 19, 2022 at 06:01:24PM +0000, Matthew Wilcox wrote: > > > On Wed, Jan 19, 2022 at 05:54:15PM +0000, Russell King (Oracle) wrote: > > > > On Wed, Jan 19, 2022 at 04:27:32PM +0000, Matthew Wilcox wrote: > > > > > On Wed, Jan 19, 2022 at 01:28:14PM +0000, Robin Murphy wrote: > > > > > > > + if (WARN_ON(!pfn_valid(page_to_pfn(page)))) > > > > > > > > > > > > Is it page_to_pfn() guaranteed to work without blowing up if page is invalid > > > > > > in the first place? Looking at the CONFIG_SPARSEMEM case I'm not sure that's > > > > > > true... > > > > > > > > > > Even if it does blow up, at least it's blowing up here where someone > > > > > can start to debug it, rather than blowing up on first access, where > > > > > we no longer have the invlid struct page pointer. > > > > > > > > > > I don't think we have a 'page_valid' function which will tell us whether > > > > > a random pointer is actually a struct page or not. > > > > > > > > Isn't it supposed to be: > > > > > > > > if (!pfn_valid(pfn)) { > > > > handle invalid pfn; > > > > } > > > > > > > > page = pfn_to_page(pfn); > > > > > > > > Anything else - even trying to convert an invalid page back to a pfn, > > > > could well be unreliable (sparsemem or discontigmem). > > > > > > This function is passed an array of pages. We have no way of doing > > > what you propose. > > > > You can't go from a struct page to "this is valid", it's too late by the > > time you call vmap() - that's my fundamental point. > > Yes, and we have debugging code in __virt_to_phys() that would have > caught this, had Yury enabled CONFIG_DEBUG_VIRTUAL. My point is that > in this instance, page_to_pfn() doesn't crash, which lets vmap() set > up a mapping to a completely bogus physical address. We're better > off checking pfn_valid() here than not. I don't disagree that pfn_valid() will catch _some_ but it should, no, must not be a subsitute for ensuring that the proper checks are done when creating e.g. an array of struct pages. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!