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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 86472C3F2CD for ; Fri, 6 Mar 2020 06:28:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BCBA208CD for ; Fri, 6 Mar 2020 06:28:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583476115; bh=HsWBsc0GnJLW6GgJ9g67UR6KTXO6F4CT0S1N9IC7YZw=; h=Date:From:To:Subject:In-Reply-To:List-ID:From; b=OTQgtSazvfY+xqzctVQiYIIcLeOo5/gvhiR71umLgfii3b2jeR5PKe5a20V9zsbyq JwoyDvQ8Ir++TfJKbR6aVqAnt6g3PEhlNv79ZpZlHAR0sPJe0oJiy2ldDscleZzc/j pU7/NhID+wJmM1GkmMt09GEXwgEZ/F5ICMXfDu18= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726485AbgCFG2f (ORCPT ); Fri, 6 Mar 2020 01:28:35 -0500 Received: from mail.kernel.org ([198.145.29.99]:36280 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725853AbgCFG2e (ORCPT ); Fri, 6 Mar 2020 01:28:34 -0500 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 29B9E208C3; Fri, 6 Mar 2020 06:28:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583476114; bh=HsWBsc0GnJLW6GgJ9g67UR6KTXO6F4CT0S1N9IC7YZw=; h=Date:From:To:Subject:In-Reply-To:From; b=TQHigk8ZEET6pTTUxChWNvpiEPfdE1XWNKxHeIFdVmPLKQefFUjW3qdGg5IeBIoIG +5oALheOhOMfjrvxB7k6b0GCPsD16HXllaep4u3HoBO0YlKNapq/787XzoitTOxk1t J9fK0SOfOYWUCIdTE2Nik1teA7QsfX7HTSXFQ6L4= Date: Thu, 05 Mar 2020 22:28:32 -0800 From: Andrew Morton To: akpm@linux-foundation.org, dan.j.williams@intel.com, jmoyer@redhat.com, Justin.He@arm.com, kirill.shutemov@linux.intel.com, kirill@shutemov.name, linux-mm@kvack.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 3/7] mm: avoid data corruption on CoW fault into PFN-mapped VMA Message-ID: <20200306062832.Eauf-skRC%akpm@linux-foundation.org> In-Reply-To: <20200305222751.6d781a3f2802d79510941e4e@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Kirill A. Shutemov" Subject: mm: avoid data corruption on CoW fault into PFN-mapped VMA 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. Link: http://lkml.kernel.org/r/20200218154151.13349-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Reported-by: Jeff Moyer Tested-by: Jeff Moyer Cc: Dan Williams Cc: Justin He Cc: Signed-off-by: Andrew Morton --- mm/memory.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) --- a/mm/memory.c~mm-avoid-data-corruption-on-cow-fault-into-pfn-mapped-vma +++ a/mm/memory.c @@ -2257,7 +2257,7 @@ static inline bool cow_user_page(struct 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 * 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 * 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); _