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    Subject[PATCH 5.15 506/917] s390/gmap: validate VMA in __gmap_zap()
    Date
    From: David Hildenbrand <david@redhat.com>

    [ Upstream commit 2d8fb8f3914b40e3cc12f8cbb74daefd5245349d ]

    We should not walk/touch page tables outside of VMA boundaries when
    holding only the mmap sem in read mode. Evil user space can modify the
    VMA layout just before this function runs and e.g., trigger races with
    page table removal code since commit dd2283f2605e ("mm: mmap: zap pages
    with read mmap_sem in munmap"). The pure prescence in our guest_to_host
    radix tree does not imply that there is a VMA.

    Further, we should not allocate page tables (via get_locked_pte()) outside
    of VMA boundaries: if evil user space decides to map hugetlbfs to these
    ranges, bad things will happen because we suddenly have PTE or PMD page
    tables where we shouldn't have them.

    Similarly, we have to check if we suddenly find a hugetlbfs VMA, before
    calling get_locked_pte().

    Note that gmap_discard() is different:
    zap_page_range()->unmap_single_vma() makes sure to stay within VMA
    boundaries.

    Fixes: b31288fa83b2 ("s390/kvm: support collaborative memory management")
    Signed-off-by: David Hildenbrand <david@redhat.com>
    Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Acked-by: Heiko Carstens <hca@linux.ibm.com>
    Link: https://lore.kernel.org/r/20210909162248.14969-2-david@redhat.com
    Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/s390/mm/gmap.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
    index 4d3b33ce81c62..e0735c3437759 100644
    --- a/arch/s390/mm/gmap.c
    +++ b/arch/s390/mm/gmap.c
    @@ -672,6 +672,7 @@ EXPORT_SYMBOL_GPL(gmap_fault);
    */
    void __gmap_zap(struct gmap *gmap, unsigned long gaddr)
    {
    + struct vm_area_struct *vma;
    unsigned long vmaddr;
    spinlock_t *ptl;
    pte_t *ptep;
    @@ -681,6 +682,11 @@ void __gmap_zap(struct gmap *gmap, unsigned long gaddr)
    gaddr >> PMD_SHIFT);
    if (vmaddr) {
    vmaddr |= gaddr & ~PMD_MASK;
    +
    + vma = vma_lookup(gmap->mm, vmaddr);
    + if (!vma || is_vm_hugetlb_page(vma))
    + return;
    +
    /* Get pointer to the page table entry */
    ptep = get_locked_pte(gmap->mm, vmaddr, &ptl);
    if (likely(ptep))
    --
    2.33.0


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