From: Fan Yang Date: Thu, 4 Jun 2020 18:22:07 +0800 Subject: mm: Fix mremap not considering huge pmd devmap Origin: https://git.kernel.org/linus/5bfea2d9b17f1034a68147a8b03b9789af5700f9 Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-10757 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: Reported-by: Fan Yang Signed-off-by: Fan Yang Tested-by: Fan Yang Tested-by: Dan Williams Reviewed-by: Dan Williams Acked-by: Kirill A. Shutemov Signed-off-by: Linus Torvalds --- arch/x86/include/asm/pgtable.h | 1 + mm/mremap.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index f51d8997ed00..b8f46bbe69f4 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -257,6 +257,7 @@ 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; diff --git a/mm/mremap.c b/mm/mremap.c index 6aa6ea605068..57b1f999f789 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -266,7 +266,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, 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() */ -- 2.27.0.rc0