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52 lines
2.0 KiB
Diff
52 lines
2.0 KiB
Diff
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From ee53664bda169f519ce3c6a22d378f0b946c8178 Mon Sep 17 00:00:00 2001
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From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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Date: Fri, 20 Dec 2013 15:10:03 +0200
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Subject: [PATCH] mm: Fix NULL pointer dereference in madvise(MADV_WILLNEED)
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support
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Sasha Levin found a NULL pointer dereference that is due to a missing
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page table lock, which in turn is due to the pmd entry in question being
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a transparent huge-table entry.
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The code - introduced in commit 1998cc048901 ("mm: make
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madvise(MADV_WILLNEED) support swap file prefetch") - correctly checks
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for this situation using pmd_none_or_trans_huge_or_clear_bad(), but it
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turns out that that function doesn't work correctly.
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pmd_none_or_trans_huge_or_clear_bad() expected that pmd_bad() would
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trigger if the transparent hugepage bit was set, but it doesn't do that
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if pmd_numa() is also set. Note that the NUMA bit only gets set on real
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NUMA machines, so people trying to reproduce this on most normal
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development systems would never actually trigger this.
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Fix it by removing the very subtle (and subtly incorrect) expectation,
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and instead just checking pmd_trans_huge() explicitly.
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Reported-by: Sasha Levin <sasha.levin@oracle.com>
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Acked-by: Andrea Arcangeli <aarcange@redhat.com>
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[ Additionally remove the now stale test for pmd_trans_huge() inside the
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pmd_bad() case - Linus ]
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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include/asm-generic/pgtable.h | 5 ++---
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1 file changed, 2 insertions(+), 3 deletions(-)
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diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
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index b12079afbd5f2..db09234589409 100644
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--- a/include/asm-generic/pgtable.h
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+++ b/include/asm-generic/pgtable.h
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@@ -599,11 +599,10 @@ static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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barrier();
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#endif
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- if (pmd_none(pmdval))
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+ if (pmd_none(pmdval) || pmd_trans_huge(pmdval))
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return 1;
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if (unlikely(pmd_bad(pmdval))) {
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- if (!pmd_trans_huge(pmdval))
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- pmd_clear_bad(pmd);
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+ pmd_clear_bad(pmd);
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return 1;
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}
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return 0;
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