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))