Patch "mm: migrate: Close race between migration completion and mprotect" has been added to the 3.16-stable tree

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This is a note to let you know that I've just added the patch titled

    mm: migrate: Close race between migration completion and mprotect

to the 3.16-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-migrate-close-race-between-migration-completion-and-mprotect.patch
and it can be found in the queue-3.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From d3cb8bf6081b8b7a2dabb1264fe968fd870fa595 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@xxxxxxx>
Date: Thu, 2 Oct 2014 19:47:41 +0100
Subject: mm: migrate: Close race between migration completion and mprotect

From: Mel Gorman <mgorman@xxxxxxx>

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@xxxxxxxxxxxxxxxxxxxx: use maybe_mkwrite]
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/migrate.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -146,8 +146,11 @@ static int remove_migration_pte(struct p
 	pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
 	if (pte_swp_soft_dirty(*ptep))
 		pte = pte_mksoft_dirty(pte);
+
+	/* 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);


Patches currently in stable-queue which might be from mgorman@xxxxxxx are

queue-3.16/mm-migrate-close-race-between-migration-completion-and-mprotect.patch
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