ACK: [CVE-2017-1000405 artful] mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()
Stefan Bader
stefan.bader at canonical.com
Mon Dec 4 10:17:11 UTC 2017
On 01.12.2017 21:10, Thadeu Lima de Souza Cascardo wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov at linux.intel.com>
>
> Currently, we unconditionally make page table dirty in touch_pmd().
> It may result in false-positive can_follow_write_pmd().
>
> We may avoid the situation, if we would only make the page table entry
> dirty if caller asks for write access -- FOLL_WRITE.
>
> The patch also changes touch_pud() in the same way.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: Hugh Dickins <hughd at google.com>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> (cherry picked from commit a8f97366452ed491d13cf1e44241bc0b5740b1f0)
> CVE-2017-1000405
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>
> Reproducer has been tested. It "exploits" without the patch. With the patch, it
> fails.
Cherry pick and tested.
>
> ---
> mm/huge_memory.c | 36 +++++++++++++-----------------------
> 1 file changed, 13 insertions(+), 23 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 90731e3b7e58..8b887db33383 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -842,20 +842,15 @@ EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud);
> #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>
> static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
> - pmd_t *pmd)
> + pmd_t *pmd, int flags)
> {
> pmd_t _pmd;
>
> - /*
> - * We should set the dirty bit only for FOLL_WRITE but for now
> - * the dirty bit in the pmd is meaningless. And if the dirty
> - * bit will become meaningful and we'll only set it with
> - * FOLL_WRITE, an atomic set_bit will be required on the pmd to
> - * set the young bit, instead of the current set_pmd_at.
> - */
> - _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
> + _pmd = pmd_mkyoung(*pmd);
> + if (flags & FOLL_WRITE)
> + _pmd = pmd_mkdirty(_pmd);
> if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
> - pmd, _pmd, 1))
> + pmd, _pmd, flags & FOLL_WRITE))
> update_mmu_cache_pmd(vma, addr, pmd);
> }
>
> @@ -884,7 +879,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
> return NULL;
>
> if (flags & FOLL_TOUCH)
> - touch_pmd(vma, addr, pmd);
> + touch_pmd(vma, addr, pmd, flags);
>
> /*
> * device mapped pages can only be returned if the
> @@ -973,20 +968,15 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>
> #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
> - pud_t *pud)
> + pud_t *pud, int flags)
> {
> pud_t _pud;
>
> - /*
> - * We should set the dirty bit only for FOLL_WRITE but for now
> - * the dirty bit in the pud is meaningless. And if the dirty
> - * bit will become meaningful and we'll only set it with
> - * FOLL_WRITE, an atomic set_bit will be required on the pud to
> - * set the young bit, instead of the current set_pud_at.
> - */
> - _pud = pud_mkyoung(pud_mkdirty(*pud));
> + _pud = pud_mkyoung(*pud);
> + if (flags & FOLL_WRITE)
> + _pud = pud_mkdirty(_pud);
> if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
> - pud, _pud, 1))
> + pud, _pud, flags & FOLL_WRITE))
> update_mmu_cache_pud(vma, addr, pud);
> }
>
> @@ -1009,7 +999,7 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
> return NULL;
>
> if (flags & FOLL_TOUCH)
> - touch_pud(vma, addr, pud);
> + touch_pud(vma, addr, pud, flags);
>
> /*
> * device mapped pages can only be returned if the
> @@ -1371,7 +1361,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> page = pmd_page(*pmd);
> VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
> if (flags & FOLL_TOUCH)
> - touch_pmd(vma, addr, pmd);
> + touch_pmd(vma, addr, pmd, flags);
> if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
> /*
> * We don't mlock() pte-mapped THPs. This way we can avoid
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ubuntu.com/archives/kernel-team/attachments/20171204/e0a8af50/attachment.sig>
More information about the kernel-team
mailing list