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    Subject[PATCH v22 16/28] mm: Fixup places that call pte_mkwrite() directly
    Date
    When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
    a writable vma. A shadow stack vma is writable, but its PTEs need
    _PAGE_DIRTY to be set to become writable. For this reason, maybe_mkwrite()
    has been updated.

    There are a few places that call pte_mkwrite() directly, but effect the
    same result as from maybe_mkwrite(). These sites need to be updated for
    shadow stack as well. Thus, change them to maybe_mkwrite():

    - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
    and call pte_mkwrite(), which is the same as maybe_mkwrite(). Change
    them to maybe_mkwrite().

    - In do_numa_page(), if the numa entry 'was-writable', then pte_mkwrite()
    is called directly. Fix it by doing maybe_mkwrite().

    - In change_pte_range(), pte_mkwrite() is called directly. Replace it with
    maybe_mkwrite().

    A shadow stack vma is writable but has different vma
    flags, and handled accordingly in maybe_mkwrite().

    Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    ---
    mm/memory.c | 5 ++---
    mm/migrate.c | 3 +--
    mm/mprotect.c | 2 +-
    3 files changed, 4 insertions(+), 6 deletions(-)

    diff --git a/mm/memory.c b/mm/memory.c
    index c8e357627318..0bdc6f2a8fe0 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -3559,8 +3559,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
    __SetPageUptodate(page);

    entry = mk_pte(page, vma->vm_page_prot);
    - if (vma->vm_flags & VM_WRITE)
    - entry = pte_mkwrite(pte_mkdirty(entry));
    + entry = maybe_mkwrite(pte_mkdirty(entry), vma);

    vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
    &vmf->ptl);
    @@ -4123,7 +4122,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
    pte = pte_modify(old_pte, vma->vm_page_prot);
    pte = pte_mkyoung(pte);
    if (was_writable)
    - pte = pte_mkwrite(pte);
    + pte = maybe_mkwrite(pte, vma);
    ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte);
    update_mmu_cache(vma, vmf->address, vmf->pte);

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 62b81d5257aa..7251c88a3d64 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -2976,8 +2976,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
    }
    } else {
    entry = mk_pte(page, vma->vm_page_prot);
    - if (vma->vm_flags & VM_WRITE)
    - entry = pte_mkwrite(pte_mkdirty(entry));
    + entry = maybe_mkwrite(pte_mkdirty(entry), vma);
    }

    ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
    diff --git a/mm/mprotect.c b/mm/mprotect.c
    index 94188df1ee55..c1ce78d688b6 100644
    --- a/mm/mprotect.c
    +++ b/mm/mprotect.c
    @@ -135,7 +135,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
    if (dirty_accountable && pte_dirty(ptent) &&
    (pte_soft_dirty(ptent) ||
    !(vma->vm_flags & VM_SOFTDIRTY))) {
    - ptent = pte_mkwrite(ptent);
    + ptent = maybe_mkwrite(ptent, vma);
    }
    ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
    pages++;
    --
    2.21.0
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