Commit d3cb8bf6 authored Oct 02, 2014 by Mel Gorman Committed by Linus Torvalds Oct 02, 2014

mm: migrate: Close race between migration completion and mprotect



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]
Cc: stable@vger.kernel.org
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>

parent 50dddff3

mm/migrate.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -146,8 +146,11 @@ static int remove_migration_pte(struct page new, struct vm_area_struct vma,
		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);

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