diff mbox series

[resend,RFC,1/9] s390/gmap: validate VMA in __gmap_zap()

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

Commit Message

David Hildenbrand Sept. 9, 2021, 4:22 p.m. UTC
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(+)

Comments

Claudio Imbrenda Sept. 14, 2021, 4:53 p.m. UTC | #1
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 mbox series

Patch

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))