From patchwork Tue Mar 15 14:18:30 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12781500 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 2DC2CC433F5 for ; Tue, 15 Mar 2022 14:20:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-Id:Date:Subject:Cc :To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=iv3QwLVkgsIu5oI0v3oNYEtbJXdHXri3LIrIbCl9MLA=; b=AKWY8rh1683x/S EEnpzHZR7+GQgEkzPva/er3jPB6EwPsTB+Gt750wVzOQNn9LAShHovc5OpIechPqk2aCxVyv1TNmY vpvRk21pqOIqmf3/BdPN5rjkyvNoIOXFgOdDmRYIBt3gA3gJnq2Sxq1tn64qvBLsna8zUqLZd/1ak KrOfRRyj8iMy/XlIOKlzIX3NJy/MAucIw4xLDXjg03r1mhooUomEte8wLghZ960T/18iqfr7ue7J7 bzxgQR2bvRrxlbp2xvldobGrm0lut+Rax0RLAJjNleFeWYw0RY4hdgshsWCWov/PGxsIQ0DazQ10b 8byEC+9duNkbJlQs4b8Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nU80o-009O1k-I5; Tue, 15 Mar 2022 14:18:58 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nU80i-009Nzq-V3 for linux-arm-kernel@lists.infradead.org; Tue, 15 Mar 2022 14:18:56 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647353931; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=+Anhxjy9idb7nh6PrkDUYGwvKF5JZwvP4UAdCW2cc+o=; b=WDMSQfdnJ7z/jiWOeJ/ZngcKPLbxgDGklB2XgVWhnRowbIsZgY9ob1lOLHPAsFEisF2DNf 67ux6dli8tC9dYwd6RiZEvlfmowNYT5f5NMu0GoMJFaL4WbS7BuBsh3SY2BaF/WqKGRb2b yshzTpO59znwUbqjjb0D8ULrLdbQSh4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-411-MkmlApJ_NiuLzpx0zdSZUg-1; Tue, 15 Mar 2022 10:18:50 -0400 X-MC-Unique: MkmlApJ_NiuLzpx0zdSZUg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 42DA5803D64; Tue, 15 Mar 2022 14:18:48 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id E4D804087D7E; Tue, 15 Mar 2022 14:18:38 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , Catalin Marinas , Will Deacon , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, David Hildenbrand Subject: [PATCH v1 0/7] mm: COW fixes part 3: reliable GUP R/W FOLL_GET of anonymous pages Date: Tue, 15 Mar 2022 15:18:30 +0100 Message-Id: <20220315141837.137118-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220315_071855_113493_10274E84 X-CRM114-Status: GOOD ( 26.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org More information on the general COW issues can be found at [2]. This series is based on v5.17-rc8, [1]: [PATCH v3 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap and [4]: [PATCH v2 00/15] mm: COW fixes part 2: reliable GUP pins of anonymous pages v1 is located at: https://github.com/davidhildenbrand/linux/tree/cow_fixes_part_3_v1 This series fixes memory corruptions when a GUP R/W reference (FOLL_WRITE | FOLL_GET) was taken on an anonymous page and COW logic fails to detect exclusivity of the page to then replacing the anonymous page by a copy in the page table: The GUP reference lost synchronicity with the pages mapped into the page tables. This series focuses on x86, arm64, s390x and ppc64/book3s -- other architectures are fairly easy to support by implementing __HAVE_ARCH_PTE_SWP_EXCLUSIVE. This primarily fixes the O_DIRECT memory corruptions that can happen on concurrent swapout, whereby we lose DMA reads to a page (modifying the user page by writing to it). O_DIRECT currently uses FOLL_GET for short-term (!FOLL_LONGTERM) DMA from/to a user page. In the long run, we want to convert it to properly use FOLL_PIN, and John is working on it, but that might take a while and might not be easy to backport. In the meantime, let's restore what used to work before we started modifying our COW logic: make R/W FOLL_GET references reliable as long as there is no fork() after GUP involved. This is just the natural follow-up of part 2, that will also further reduce "wrong COW" on the swapin path, for example, when we cannot remove a page from the swapcache due to concurrent writeback, or if we have two threads faulting on the same swapped-out page. Fixing O_DIRECT is just a nice side-product :) This issue, including other related COW issues, has been summarized in [3] under 2): " 2. Intra Process Memory Corruptions due to Wrong COW (FOLL_GET) It was discovered that we can create a memory corruption by reading a file via O_DIRECT to a part (e.g., first 512 bytes) of a page, concurrently writing to an unrelated part (e.g., last byte) of the same page, and concurrently write-protecting the page via clear_refs SOFTDIRTY tracking [6]. For the reproducer, the issue is that O_DIRECT grabs a reference of the target page (via FOLL_GET) and clear_refs write-protects the relevant page table entry. On successive write access to the page from the process itself, we wrongly COW the page when resolving the write fault, resulting in a loss of synchronicity and consequently a memory corruption. While some people might think that using clear_refs in this combination is a corner cases, it turns out to be a more generic problem unfortunately. For example, it was just recently discovered that we can similarly create a memory corruption without clear_refs, simply by concurrently swapping out the buffer pages [7]. Note that we nowadays even use the swap infrastructure in Linux without an actual swap disk/partition: the prime example is zram which is enabled as default under Fedora [10]. The root issue is that a write-fault on a page that has additional references results in a COW and thereby a loss of synchronicity and consequently a memory corruption if two parties believe they are referencing the same page. " We don't particularly care about R/O FOLL_GET references: they were never reliable and O_DIRECT doesn't expect to observe modifications from a page after DMA was started. Note that: * this only fixes the issue on x86, arm64, s390x and ppc64/book3s ("enterprise architectures"). Other architectures have to implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE to achieve the same. * this does *not * consider any kind of fork() after taking the reference: fork() after GUP never worked reliably with FOLL_GET. * Not losing PG_anon_exclusive during swapout was the last remaining piece. KSM already makes sure that there are no other references on a page before considering it for sharing. Page migration maintains PG_anon_exclusive and simply fails when there are additional references (freezing the refcount fails). Only swapout code dropped the PG_anon_exclusive flag because it requires more work to remember + restore it. With this series in place, most COW issues of [3] are fixed on said architectures. Other architectures can implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE fairly easily. What remains is the COW security issue on hugetlb with FOLL_GET, and SOFTDIRTY tracking. I'll tackle both (guess what?) in part 4 once part 2 and part 3 are on its way upstream. [1] https://lkml.kernel.org/r/20220131162940.210846-1-david@redhat.com [2] https://lkml.kernel.org/r/20211217113049.23850-1-david@redhat.com [3] https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com [4] https://lkml.kernel.org/r/20220315104741.63071-1-david@redhat.com David Hildenbrand (7): mm/swap: remember PG_anon_exclusive via a swp pte bit mm/debug_vm_pgtable: add tests for __HAVE_ARCH_PTE_SWP_EXCLUSIVE x86/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE arm64/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE s390/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE powerpc/pgtable: remove _PAGE_BIT_SWAP_TYPE for book3s powerpc/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE for book3s arch/arm64/include/asm/pgtable-prot.h | 1 + arch/arm64/include/asm/pgtable.h | 23 ++++++-- arch/powerpc/include/asm/book3s/64/pgtable.h | 31 ++++++++--- arch/s390/include/asm/pgtable.h | 37 ++++++++++--- arch/x86/include/asm/pgtable.h | 16 ++++++ arch/x86/include/asm/pgtable_64.h | 4 +- arch/x86/include/asm/pgtable_types.h | 5 ++ include/linux/pgtable.h | 29 +++++++++++ include/linux/swapops.h | 2 + mm/debug_vm_pgtable.c | 15 ++++++ mm/memory.c | 55 ++++++++++++++++++-- mm/rmap.c | 19 ++++--- mm/swapfile.c | 13 ++++- 13 files changed, 219 insertions(+), 31 deletions(-)