lkml.org 
[lkml]   [2014]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 3.4 71/91] mm: migrate: Close race between migration completion and mprotect
Date
From: Mel Gorman <mgorman@suse.de>

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 <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
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


\
 
 \ /
  Last update: 2014-11-27 10:21    [W:0.229 / U:1.960 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site