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    Subject[PATCH v4 09/14] mm/mprotect: Break COW PTE before changing protection
    Date
    If the PTE table is COW-ed, break it before changing the protection.

    Signed-off-by: Chih-En Lin <shiyn.lin@gmail.com>
    ---
    mm/mprotect.c | 9 +++++++++
    1 file changed, 9 insertions(+)

    diff --git a/mm/mprotect.c b/mm/mprotect.c
    index 61cf60015a8b..8b18cd0e5c5e 100644
    --- a/mm/mprotect.c
    +++ b/mm/mprotect.c
    @@ -103,6 +103,9 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
    if (pmd_trans_unstable(pmd))
    return 0;

    + if (break_cow_pte(vma, pmd, addr))
    + return 0;
    +
    /*
    * The pmd points to a regular pte so the pmd can't change
    * from under us even if the mmap_lock is only hold for
    @@ -314,6 +317,12 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
    return 1;
    if (pmd_trans_huge(pmdval))
    return 0;
    + /*
    + * If the entry point to COW-ed PTE, it's write protection bit
    + * will cause pmd_bad().
    + */
    + if (!pmd_write(pmdval))
    + return 0;
    if (unlikely(pmd_bad(pmdval))) {
    pmd_clear_bad(pmd);
    return 1;
    --
    2.34.1
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