Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754176AbaKAXBI (ORCPT ); Sat, 1 Nov 2014 19:01:08 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60074 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751487AbaKAWj0 (ORCPT ); Sat, 1 Nov 2014 18:39:26 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Mel Gorman" , "Linus Torvalds" , "Rik van Riel" Date: Sat, 01 Nov 2014 22:28:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 075/102] mm: migrate: Close race between migration completion and mprotect In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.64-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Mel Gorman 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 [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- mm/migrate.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/mm/migrate.c +++ b/mm/migrate.c @@ -141,8 +141,11 @@ static int remove_migration_pte(struct p 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/