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    Subject[PATCH 4.19 03/28] mm: Fix mremap not considering huge pmd devmap
    Date
    From: Fan Yang <Fan_Yang@sjtu.edu.cn>

    commit 5bfea2d9b17f1034a68147a8b03b9789af5700f9 upstream.

    The original code in mm/mremap.c checks huge pmd by:

    if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd)) {

    However, a DAX mapped nvdimm is mapped as huge page (by default) but it
    is not transparent huge page (_PAGE_PSE | PAGE_DEVMAP). This commit
    changes the condition to include the case.

    This addresses CVE-2020-10757.

    Fixes: 5c7fb56e5e3f ("mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd")
    Cc: <stable@vger.kernel.org>
    Reported-by: Fan Yang <Fan_Yang@sjtu.edu.cn>
    Signed-off-by: Fan Yang <Fan_Yang@sjtu.edu.cn>
    Tested-by: Fan Yang <Fan_Yang@sjtu.edu.cn>
    Tested-by: Dan Williams <dan.j.williams@intel.com>
    Reviewed-by: Dan Williams <dan.j.williams@intel.com>
    Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/pgtable.h | 1 +
    mm/mremap.c | 2 +-
    2 files changed, 2 insertions(+), 1 deletion(-)

    --- a/arch/x86/include/asm/pgtable.h
    +++ b/arch/x86/include/asm/pgtable.h
    @@ -237,6 +237,7 @@ static inline int pmd_large(pmd_t pte)
    }

    #ifdef CONFIG_TRANSPARENT_HUGEPAGE
    +/* NOTE: when predicate huge page, consider also pmd_devmap, or use pmd_large */
    static inline int pmd_trans_huge(pmd_t pmd)
    {
    return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
    --- a/mm/mremap.c
    +++ b/mm/mremap.c
    @@ -221,7 +221,7 @@ unsigned long move_page_tables(struct vm
    new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
    if (!new_pmd)
    break;
    - if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd)) {
    + if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
    if (extent == HPAGE_PMD_SIZE) {
    bool moved;
    /* See comment in move_ptes() */

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