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    Subject[PATCH v2 2/5] uprobes: __replace_page() should not use page_address_in_vma()
    page_address_in_vma(old_page) in __replace_page() is ugly and wrong.
    The caller already knows the correct virtual address, this page was
    found by get_user_pages(vaddr).

    However, page_address_in_vma() can actually fail if page->mapping was
    cleared by __delete_from_page_cache() after get_user_pages() returns.
    But this means the race with page reclaim, write_opcode() should not
    fail, it should retry and read this page again. Not sure this race is
    really possible though, page_freeze_refs() logic should prevent it.

    We could change __replace_page() to return -EAGAIN in this case, but
    it would be better to simply use the caller's vaddr and rely on
    page_check_address().

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---
    kernel/events/uprobes.c | 11 ++++-------
    1 files changed, 4 insertions(+), 7 deletions(-)

    diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    index a2b32a5..6fda799 100644
    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -127,22 +127,19 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
    * based on replace_page in mm/ksm.c
    *
    * @vma: vma that holds the pte pointing to page
    + * @addr: address the old @page is mapped at
    * @page: the cowed page we are replacing by kpage
    * @kpage: the modified page we replace page by
    *
    * Returns 0 on success, -EFAULT on failure.
    */
    -static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
    +static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
    + struct page *page, struct page *kpage)
    {
    struct mm_struct *mm = vma->vm_mm;
    - unsigned long addr;
    spinlock_t *ptl;
    pte_t *ptep;

    - addr = page_address_in_vma(page, vma);
    - if (addr == -EFAULT)
    - return -EFAULT;
    -
    ptep = page_check_address(page, mm, addr, &ptl, 0);
    if (!ptep)
    return -EAGAIN;
    @@ -243,7 +240,7 @@ retry:
    goto unlock_out;

    lock_page(new_page);
    - ret = __replace_page(vma, old_page, new_page);
    + ret = __replace_page(vma, vaddr, old_page, new_page);
    unlock_page(new_page);

    unlock_out:
    --
    1.5.5.1



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