From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932132AbaK0Itk (ORCPT ); Thu, 27 Nov 2014 03:49:40 -0500 Received: from mail.kernel.org ([198.145.19.201]:42556 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932094AbaK0Itf (ORCPT ); Thu, 27 Nov 2014 03:49:35 -0500 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Mel Gorman , Linus Torvalds , Zefan Li Subject: [PATCH 3.4 71/91] mm: migrate: Close race between migration completion and mprotect Date: Thu, 27 Nov 2014 16:42:54 +0800 Message-Id: <1417077794-9299-71-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1417077368-9217-1-git-send-email-lizf@kernel.org> References: <1417077368-9217-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mel Gorman 3.4.105-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit d3cb8bf6081b8b7a2dabb1264fe968fd870fa595 upstream. A migration entry is marked as write if pte_write was true at the time the entry was created. The VMA protections are not double checked when migration entries are being removed as mprotect marks write-migration-entries as read. It means that potentially we take a spurious fault to mark PTEs write again but it's straight-forward. However, there is a race between write migrations being marked read and migrations finishing. This potentially allows a PTE to be write that should have been read. Close this race by double checking the VMA permissions using maybe_mkwrite when migration completes. [torvalds@linux-foundation.org: use maybe_mkwrite] Signed-off-by: Mel Gorman Acked-by: Rik van Riel Signed-off-by: Linus Torvalds [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li --- mm/migrate.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index 5f588b1..98b998f 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -139,8 +139,11 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma, get_page(new); pte = pte_mkold(mk_pte(new, vma->vm_page_prot)); + + /* Recheck VMA as permissions can change since migration started */ if (is_write_migration_entry(entry)) - pte = pte_mkwrite(pte); + pte = maybe_mkwrite(pte, vma); + #ifdef CONFIG_HUGETLB_PAGE if (PageHuge(new)) pte = pte_mkhuge(pte); -- 1.9.1