| Message ID | 20210909162248.14969-2-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | s390: fixes, cleanups and optimizations for page table walkers | expand |
On Thu, 9 Sep 2021 18:22:40 +0200 David Hildenbrand <david@redhat.com> wrote: > 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> > --- > 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 9bb2c7512cd5..b6b56cd4ca64 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -673,6 +673,7 @@ 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; > @@ -682,6 +683,11 @@ 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))
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index 9bb2c7512cd5..b6b56cd4ca64 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -673,6 +673,7 @@ 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; @@ -682,6 +683,11 @@ 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))
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> --- arch/s390/mm/gmap.c | 6 ++++++ 1 file changed, 6 insertions(+)