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 3CA16C433EF for ; Wed, 19 Jan 2022 18:57:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356944AbiASS56 (ORCPT ); Wed, 19 Jan 2022 13:57:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230509AbiASS55 (ORCPT ); Wed, 19 Jan 2022 13:57:57 -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 63925C061574 for ; Wed, 19 Jan 2022 10:57:56 -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=cnpaAt1fKMl1zfeZ6oYSZ0wXrQMMc1n5lVigEXv+DUU=; b=R7DbELeFhBokcuMuG0IWS/h4e3 mVeVGr0jpJTj8M15zPOlAAmhKKqqRHsJfyvVRO8D9NdmzNDoN+CGiRgvIpZqhCZg0g8MdmLWZf69w QJ7aftts5mS1hksdw1nT2aXrZelA30IbNESeChq2H1cVerCJftjLduosZ10MeDMs0VwyTdz6h3Blh KqC1cpuBkDEtTroZfxD9XGiSoYgHYBe+aVqz8qleaxgT5jEdC2fCQC5oDO278Jy0FYcCmJB5ZZakF QwRrzAQoSaYRjXXyh8VUsZ9n+gwZ73qvIirmlq2W8B3abTRXJfCKkZCuvcR5LGVWWOJ8d5ht9k6L+ N7ehajQQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:56782) 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 1nAG9N-00052m-QF; Wed, 19 Jan 2022 18:57:41 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1nAG9G-0005U9-Mi; Wed, 19 Jan 2022 18:57:34 +0000 Date: Wed, 19 Jan 2022 18:57:34 +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 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. If the translation from a PFN to a struct page can return pointers to something that isn't a valid struct page, then it can also (with sparsemem) return a pointer to _another_ struct page that could well be valid depending on how the struct page arrays are laid out in memory. To repeat: once you have a struct page, it's too late to determine if the struct page is valid. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!