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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 E6E00C34026 for ; Tue, 18 Feb 2020 15:41:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B60CB22527 for ; Tue, 18 Feb 2020 15:41:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="QinxkUM/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726528AbgBRPld (ORCPT ); Tue, 18 Feb 2020 10:41:33 -0500 Received: from mail-lj1-f196.google.com ([209.85.208.196]:40087 "EHLO mail-lj1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726338AbgBRPld (ORCPT ); Tue, 18 Feb 2020 10:41:33 -0500 Received: by mail-lj1-f196.google.com with SMTP id n18so23476009ljo.7 for ; Tue, 18 Feb 2020 07:41:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=1prNYVi8te7tpWxKFgmK7lDkMWxtco2vgGigTJkyqhk=; b=QinxkUM/O6Civ5jQpx/cuVNRO8J5+mvs4duVtsr3xz9OrwvnLc9JOcvO6b31sBwh5m HZdxicIZPBgdplsEFqpPqBDAx7PMuK8KJe84FhsQ/nH1OxAC0bzLqimtyli5Gmy9wcGA 47/hc/xCOk8pTbcfL8fVKVf/M3a4YLzIyhX8Vq+nyG/1Ux0XmTrXwbZkxxiTmZ/1qyUZ N7jZqgWGM/FxrBvEEIsy/c9VIELiYV6+KzSNNgMudKPN0zT7rCvqbdk75w77kXu1mG8A BN9eGYn7q15twXvI7aLSaKQoZEhJdNplhvwvqpeUudiziyCVyzNvmTHsbenQr4yhWu4g X1sg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=1prNYVi8te7tpWxKFgmK7lDkMWxtco2vgGigTJkyqhk=; b=MKIxRgdmJ79VQEsqRmCpFKJdQr0YaBLIZmhFcFATbkxsEs2RUkBiL7wGJ6omslgIrR JlyZMz25pTgDobh1CLevOoPavota38hayKFlA2mqW5MTby4hz/RldNYkLyRsH5+VQ79K Jbm30CD+r9DCs/5l0Q0bKDbIplhRXa1nbr5JZQ5OXg9mXELIQ+hODqqI6SYsCk3yAHy+ s87goj0eZAPXFVNPCLuNicahDJnVdbaQjI3IyOhI+SyAMMoqaTCvlI830HABKwCovooy NQqBLPjcLKPUeOu6t5P19pNlE6wMcUYyKuJsLRoVduSgAmD3Cd6Tc4H3CnTDyWyFYvYU bCcw== X-Gm-Message-State: APjAAAV2gpeQ1ZetYNfSz0m36SYor+FLWKtKpG2oiIq4zQkl7EX/9inc 8KvbJQq8n4vATGXPTGEgtiJv+gWK3vk= X-Google-Smtp-Source: APXvYqy02bAtARqs+xW5We+9JpED8EM7JDMzMhWAW6eWMmMGlvg2dNW69eQ4eWi532XnQLXF9CeDTA== X-Received: by 2002:a2e:80cc:: with SMTP id r12mr12507646ljg.154.1582040489372; Tue, 18 Feb 2020 07:41:29 -0800 (PST) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id b1sm2932370ljp.72.2020.02.18.07.41.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Feb 2020 07:41:28 -0800 (PST) From: "Kirill A. Shutemov" X-Google-Original-From: "Kirill A. Shutemov" Received: by box.localdomain (Postfix, from userid 1000) id 5F99E100FA3; Tue, 18 Feb 2020 18:41:56 +0300 (+03) To: Andrew Morton Cc: Dan Williams , Justin He , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Jeff Moyer Subject: [PATCH] mm: Avoid data corruption on CoW fault into PFN-mapped VMA Date: Tue, 18 Feb 2020 18:41:51 +0300 Message-Id: <20200218154151.13349-1-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeff Moyer has reported that one of xfstests triggers a warning when run on DAX-enabled filesystem: WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50 ... wp_page_copy+0x98c/0xd50 (unreliable) do_wp_page+0xd8/0xad0 __handle_mm_fault+0x748/0x1b90 handle_mm_fault+0x120/0x1f0 __do_page_fault+0x240/0xd70 do_page_fault+0x38/0xd0 handle_page_fault+0x10/0x30 The warning happens on failed __copy_from_user_inatomic() which tries to copy data into a CoW page. This happens because of race between MADV_DONTNEED and CoW page fault: CPU0 CPU1 handle_mm_fault() do_wp_page() wp_page_copy() do_wp_page() madvise(MADV_DONTNEED) zap_page_range() zap_pte_range() ptep_get_and_clear_full() __copy_from_user_inatomic() sees empty PTE and fails WARN_ON_ONCE(1) clear_page() The solution is to re-try __copy_from_user_inatomic() under PTL after checking that PTE is matches the orig_pte. The second copy attempt can still fail, like due to non-readable PTE, but there's nothing reasonable we can do about, except clearing the CoW page. Signed-off-by: Kirill A. Shutemov Reported-and-tested-by: Jeff Moyer --- mm/memory.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 0bccc622e482..e8bfdf0d9d1d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2257,7 +2257,7 @@ static inline bool cow_user_page(struct page *dst, struct page *src, bool ret; void *kaddr; void __user *uaddr; - bool force_mkyoung; + bool locked = false; struct vm_area_struct *vma = vmf->vma; struct mm_struct *mm = vma->vm_mm; unsigned long addr = vmf->address; @@ -2282,11 +2282,11 @@ static inline bool cow_user_page(struct page *dst, struct page *src, * On architectures with software "accessed" bits, we would * take a double page fault, so mark it accessed here. */ - force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte); - if (force_mkyoung) { + if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { pte_t entry; vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); + locked = true; if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { /* * Other thread has already handled the fault @@ -2310,18 +2310,37 @@ static inline bool cow_user_page(struct page *dst, struct page *src, * zeroes. */ if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + if (locked) + goto warn; + + /* Re-validate under PTL if the page is still mapped */ + vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); + locked = true; + if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { + /* The PTE changed under us. Retry page fault. */ + ret = false; + goto pte_unlock; + } + /* - * Give a warn in case there can be some obscure - * use-case + * The same page can be mapped back since last copy attampt. + * Try to copy again under PTL. */ - WARN_ON_ONCE(1); - clear_page(kaddr); + if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + /* + * Give a warn in case there can be some obscure + * use-case + */ +warn: + WARN_ON_ONCE(1); + clear_page(kaddr); + } } ret = true; pte_unlock: - if (force_mkyoung) + if (locked) pte_unmap_unlock(vmf->pte, vmf->ptl); kunmap_atomic(kaddr); flush_dcache_page(dst); -- 2.25.1