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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 F1251C433E0 for ; Mon, 1 Feb 2021 10:51:21 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 906B960C41 for ; Mon, 1 Feb 2021 10:51:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 906B960C41 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=e2u6MRLKGWqs/pOTJzq835B5JckF4Uc0ktmIEaUOYZQ=; b=u5TltVBEDAWB3082piq9oWwQ9 zFNeI5qUassvVqc4oH92dtz4PLPF/btb1kQATtxoPwvH9sMDKc00IKZFtXtcn5UGl8ymYcizfFYCQ sCLkPE5MB0a/nqF+LreI0TdbcmwGN/R4t6/IwgneAH7SsNERC/2Kgsef+qrWw9Jip0YUp7T6LQPtd Hhy6lJaprwQhv24i2ywEs8/ckFfsSDmDr9Vy6guJI860aFo5IVUL8mDD+Va2V22RqZbFn+IzhdClI wNBr4QncLj8fXjLoKVziF+KWjSGnj0w7OuAC1KJ7k/PNPn0T3KXE9NnH5pDoSsRyqoTMFPxPHDbt8 Eya7G/Usw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l6WmZ-0004xk-55; Mon, 01 Feb 2021 10:50:11 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l6WmV-0004xI-P8 for linux-arm-kernel@lists.infradead.org; Mon, 01 Feb 2021 10:50:08 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 71A2C64DD8; Mon, 1 Feb 2021 10:50:05 +0000 (UTC) Date: Mon, 1 Feb 2021 10:50:02 +0000 From: Catalin Marinas To: Ard Biesheuvel Subject: Re: [GIT PULL] arm64 fixes for 5.11-rc6 Message-ID: <20210201105001.GA13756@gaia> References: <20210129190322.GA4590@gaia> <20210131185443.GA29083@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210201_055008_029067_ACCB99B8 X-CRM114-Status: GOOD ( 32.31 ) 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: Will Deacon , Lorenzo Pieralisi , Linus Torvalds , Linux Kernel Mailing List , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 01, 2021 at 12:07:52AM +0100, Ard Biesheuvel wrote: > On Sun, 31 Jan 2021 at 19:55, Catalin Marinas wrote: > > On Fri, Jan 29, 2021 at 02:09:05PM -0800, Linus Torvalds wrote: > > > On Fri, Jan 29, 2021 at 11:03 AM Catalin Marinas > > > wrote: > > > > > > > > arm64 fixes: > > > > > > > > - Fix the virt_addr_valid() returning true for < PAGE_OFFSET addresses. > > > > > > That's a really odd fix. > > > > > > It went from an incorrect bitwise operation (masking) to an _odd_ > > > bitwise operation (xor). > > > > > > Yes, PAGE_OFFSET has the bit pattern of all upper bits set, so "(addr > > > ^ PAGE_OFFSET)" by definition reverses the upper bits - and for a > > > valid case turns them to zero. > > > > > > But isn't the *logical* thing to do to use a subtract instead? For the > > > valid cases, the two do the same thing (clear the upper bits), but > > > just conceptually, isn't the operation that you actually want to do > > > "(addr - PAGE_OFFSET)"? > > > > > > IOW, why is it using that odd xor pattern that doesn't make much > > > sense? I believe it _works_, but it looks very strange to me. > > > > This macro used to test a single bit and it evolved into a bitmask. So, > > yes, basically what we need is: > > > > #define __is_lm_address(addr) ((u64)(addr) >= PAGE_OFFSET && \ > > (u64)(addr) < PAGE_END) > > > > I wasn't sure whether the code generation with two comparisons is > > similar to the xor variant but the compiler should probably be smart > > enough to use CMP and CCMP. In the grand scheme, it probably doesn't > > even matter. > > > > Unless I miss something, I don't see any overflow issues even if we do > > (((u64)addr - PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)). > > > > We can backport the fix already upstream and clean-up the code in > > mainline going forward (after some sanity check on the code generation). > > It would be easier to parse in the future. > > > > > Also, shouldn't _lm_to_phys() do the same? It does that "mask upper > > > bits" too that was problematic in __is_lm_address(). Again, shouldn't > > > that logically be a subtract op? > > > > Yes, that's similar and a subtract should do. > > The original bit test was written like that because it removes the > need to reason about a potential tag in the upper bits. I tried to > preserve that behavior when removing the guaranteed 1:1 split between > the vmalloc and linear regions, by masking with PAGE_OFFSET and > comparing with PAGE_END - PAGE_OFFSET, but unfortunately, both > approaches suffer from the issue fixed by this patch, i.e., that > virt_addr_valid(0x0) erroneously returns true. > > I think both proposed fixes are appropriate, but they both reintroduce > the need to consider the tag. I don't know whether or where this could > pose a problem, but it needs to be taken into account. I think we get away with this but should be fixed. For example, virt_addr_valid() call in slab.c depends on DEBUG_SLAB but KASAN (which generates kernel tagged addresses) depends on !DEBUG_SLAB. Some of the uaccess hardening like check_object_size() -> check_heap_object() may be skipped but no error. Anyway, I'll write a patch to cover tagged kernel addresses as well. When the linear map was at the top of the address range, we used to have: #define _virt_addr_is_linear(kaddr) \ (__tag_reset((u64)(kaddr)) >= PAGE_OFFSET) Afterwards we kept the tagged addresses in mind (well, until the recent "fix") but lost the check against user addresses with commit 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using __is_lm_address()"). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel