Re: [PATCH resend RFC 3/9] s390/mm: validate VMA in PGSTE manipulation functions

[Claudio Imbrenda]

On Thu,  9 Sep 2021 18:22:42 +0200
David Hildenbrand <david@xxxxxxxxxx> 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"). gfn_to_hva() will only translate using
> KVM memory regions, but won't validate the VMA.
> 
> Further, we should not allocate page tables 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().
> 
> Fixes: 2d42f9477320 ("s390/kvm: Add PGSTE manipulation functions")
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

> ---
>  arch/s390/mm/pgtable.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
> index eec3a9d7176e..54969e0f3a94 100644
> --- a/arch/s390/mm/pgtable.c
> +++ b/arch/s390/mm/pgtable.c
> @@ -988,6 +988,7 @@ EXPORT_SYMBOL(get_guest_storage_key);
>  int pgste_perform_essa(struct mm_struct *mm, unsigned long hva, int orc,
>  			unsigned long *oldpte, unsigned long *oldpgste)
>  {
> +	struct vm_area_struct *vma;
>  	unsigned long pgstev;
>  	spinlock_t *ptl;
>  	pgste_t pgste;
> @@ -997,6 +998,10 @@ int pgste_perform_essa(struct mm_struct *mm, unsigned long hva, int orc,
>  	WARN_ON_ONCE(orc > ESSA_MAX);
>  	if (unlikely(orc > ESSA_MAX))
>  		return -EINVAL;
> +
> +	vma = vma_lookup(mm, hva);
> +	if (!vma || is_vm_hugetlb_page(vma))
> +		return -EFAULT;
>  	ptep = get_locked_pte(mm, hva, &ptl);
>  	if (unlikely(!ptep))
>  		return -EFAULT;
> @@ -1089,10 +1094,14 @@ EXPORT_SYMBOL(pgste_perform_essa);
>  int set_pgste_bits(struct mm_struct *mm, unsigned long hva,
>  			unsigned long bits, unsigned long value)
>  {
> +	struct vm_area_struct *vma;
>  	spinlock_t *ptl;
>  	pgste_t new;
>  	pte_t *ptep;
>  
> +	vma = vma_lookup(mm, hva);
> +	if (!vma || is_vm_hugetlb_page(vma))
> +		return -EFAULT;
>  	ptep = get_locked_pte(mm, hva, &ptl);
>  	if (unlikely(!ptep))
>  		return -EFAULT;
> @@ -1117,9 +1126,13 @@ EXPORT_SYMBOL(set_pgste_bits);
>   */
>  int get_pgste(struct mm_struct *mm, unsigned long hva, unsigned long *pgstep)
>  {
> +	struct vm_area_struct *vma;
>  	spinlock_t *ptl;
>  	pte_t *ptep;
>  
> +	vma = vma_lookup(mm, hva);
> +	if (!vma || is_vm_hugetlb_page(vma))
> +		return -EFAULT;
>  	ptep = get_locked_pte(mm, hva, &ptl);
>  	if (unlikely(!ptep))
>  		return -EFAULT;