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    Subject[RFC PATCH v2 16/27] mm: Modify can_follow_write_pte/pmd for shadow stack
    Date
    There are three possible shadow stack PTE settings:

    Normal SHSTK PTE: (R/O + DIRTY_HW)
    SHSTK PTE COW'ed: (R/O + DIRTY_HW)
    SHSTK PTE shared as R/O data: (R/O + DIRTY_SW)

    Update can_follow_write_pte/pmd for the shadow stack.

    Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
    ---
    mm/gup.c | 11 ++++++++---
    mm/huge_memory.c | 10 +++++++---
    2 files changed, 15 insertions(+), 6 deletions(-)

    diff --git a/mm/gup.c b/mm/gup.c
    index b70d7ba7cc13..00171ee847af 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -64,10 +64,13 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
    * FOLL_FORCE can write to even unwritable pte's, but only
    * after we've gone through a COW cycle and they are dirty.
    */
    -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
    +static inline bool can_follow_write_pte(pte_t pte, unsigned int flags,
    + bool shstk)
    {
    + bool pte_cowed = shstk ? is_shstk_pte(pte):pte_dirty(pte);
    +
    return pte_write(pte) ||
    - ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
    + ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_cowed);
    }

    static struct page *follow_page_pte(struct vm_area_struct *vma,
    @@ -78,7 +81,9 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
    struct page *page;
    spinlock_t *ptl;
    pte_t *ptep, pte;
    + bool shstk;

    + shstk = is_shstk_mapping(vma->vm_flags);
    retry:
    if (unlikely(pmd_bad(*pmd)))
    return no_page_table(vma, flags);
    @@ -105,7 +110,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
    }
    if ((flags & FOLL_NUMA) && pte_protnone(pte))
    goto no_page;
    - if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
    + if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags, shstk)) {
    pte_unmap_unlock(ptep, ptl);
    return NULL;
    }
    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index 7f3e11d3b64a..db4c689a960a 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1389,10 +1389,13 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
    * FOLL_FORCE can write to even unwritable pmd's, but only
    * after we've gone through a COW cycle and they are dirty.
    */
    -static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
    +static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags,
    + bool shstk)
    {
    + bool pmd_cowed = shstk ? is_shstk_pmd(pmd):pmd_dirty(pmd);
    +
    return pmd_write(pmd) ||
    - ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
    + ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_cowed);
    }

    struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
    @@ -1402,10 +1405,11 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
    {
    struct mm_struct *mm = vma->vm_mm;
    struct page *page = NULL;
    + bool shstk = is_shstk_mapping(vma->vm_flags);

    assert_spin_locked(pmd_lockptr(mm, pmd));

    - if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
    + if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags, shstk))
    goto out;

    /* Avoid dumping huge zero page */
    --
    2.17.1
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