Merge tag 'kvm-s390-next-6.4-2' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

For 6.4

3 files changed, 23 insertions, 21 deletions

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f18a4af9c13..cb2ee06df286 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -192,21 +192,10 @@ static int expected_page_refs(struct page *page)
 	return res;
 }
 
-static int make_secure_pte(pte_t *ptep, unsigned long addr,
-			   struct page *exp_page, struct uv_cb_header *uvcb)
+static int make_page_secure(struct page *page, struct uv_cb_header *uvcb)
 {
-	pte_t entry = READ_ONCE(*ptep);
-	struct page *page;
 	int expected, cc = 0;
 
-	if (!pte_present(entry))
-		return -ENXIO;
-	if (pte_val(entry) & _PAGE_INVALID)
-		return -ENXIO;
-
-	page = pte_page(entry);
-	if (page != exp_page)
-		return -ENXIO;
 	if (PageWriteback(page))
 		return -EAGAIN;
 	expected = expected_page_refs(page);
@@ -304,17 +293,18 @@ again:
 		goto out;
 
 	rc = -ENXIO;
-	page = follow_page(vma, uaddr, FOLL_WRITE);
-	if (IS_ERR_OR_NULL(page))
-		goto out;
-
-	lock_page(page);
 	ptep = get_locked_pte(gmap->mm, uaddr, &ptelock);
-	if (should_export_before_import(uvcb, gmap->mm))
-		uv_convert_from_secure(page_to_phys(page));
-	rc = make_secure_pte(ptep, uaddr, page, uvcb);
+	if (pte_present(*ptep) && !(pte_val(*ptep) & _PAGE_INVALID) && pte_write(*ptep)) {
+		page = pte_page(*ptep);
+		rc = -EAGAIN;
+		if (trylock_page(page)) {
+			if (should_export_before_import(uvcb, gmap->mm))
+				uv_convert_from_secure(page_to_phys(page));
+			rc = make_page_secure(page, uvcb);
+			unlock_page(page);
+		}
+	}
 	pte_unmap_unlock(ptep, ptelock);
-	unlock_page(page);
 out:
 	mmap_read_unlock(gmap->mm);
 
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index e032ebbf51b9..3ce5f4351156 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -314,6 +314,11 @@ int kvm_s390_pv_set_aside(struct kvm *kvm, u16 *rc, u16 *rrc)
 	 */
 	if (kvm->arch.pv.set_aside)
 		return -EINVAL;
+
+	/* Guest with segment type ASCE, refuse to destroy asynchronously */
+	if ((kvm->arch.gmap->asce & _ASCE_TYPE_MASK) == _ASCE_TYPE_SEGMENT)
+		return -EINVAL;
+
 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 0949811761e6..8492a3f5642e 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2840,6 +2840,9 @@ EXPORT_SYMBOL_GPL(s390_unlist_old_asce);
  * s390_replace_asce - Try to replace the current ASCE of a gmap with a copy
  * @gmap: the gmap whose ASCE needs to be replaced
  *
+ * If the ASCE is a SEGMENT type then this function will return -EINVAL,
+ * otherwise the pointers in the host_to_guest radix tree will keep pointing
+ * to the wrong pages, causing use-after-free and memory corruption.
  * If the allocation of the new top level page table fails, the ASCE is not
  * replaced.
  * In any case, the old ASCE is always removed from the gmap CRST list.
@@ -2854,6 +2857,10 @@ int s390_replace_asce(struct gmap *gmap)
 
 	s390_unlist_old_asce(gmap);
 
+	/* Replacing segment type ASCEs would cause serious issues */
+	if ((gmap->asce & _ASCE_TYPE_MASK) == _ASCE_TYPE_SEGMENT)
+		return -EINVAL;
+
 	page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER);
 	if (!page)
 		return -ENOMEM;