x86/p2m: add option to skip root pagetable removal in p2m_teardown()

Add a new parameter to p2m_teardown() in order to select whether the
root page table should also be freed.  Note that all users are
adjusted to pass the parameter to remove the root page tables, so
behavior is not modified.

No functional change intended.

This is part of CVE-2022-33746 / XSA-410.

Suggested-by: Julien Grall <julien@xen.org>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
master commit: 1df52a270225527ae27bfa2fc40347bf93b78357
master date: 2022-10-11 14:21:23 +0200

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 47a7487fa7a3f87560f1b92bc46fec94abd147e2..a8f5a19da9172a2f0d5f7d396a777328fadb95d9 100644 (file)
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -541,18 +541,18 @@ void hap_final_teardown(struct domain *d)
         }
 
         for ( i = 0; i < MAX_ALTP2M; i++ )
-            p2m_teardown(d->arch.altp2m_p2m[i]);
+            p2m_teardown(d->arch.altp2m_p2m[i], true);
     }
 
     /* Destroy nestedp2m's first */
     for (i = 0; i < MAX_NESTEDP2M; i++) {
-        p2m_teardown(d->arch.nested_p2m[i]);
+        p2m_teardown(d->arch.nested_p2m[i], true);
     }
 
     if ( d->arch.paging.hap.total_pages != 0 )
         hap_teardown(d, NULL);
 
-    p2m_teardown(p2m_get_hostp2m(d));
+    p2m_teardown(p2m_get_hostp2m(d), true);
     /* Free any memory that the p2m teardown released */
     paging_lock(d);
     hap_set_allocation(d, 0, NULL);

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index def1695cf00b0a13d047a55a1afc5c451d9667a6..aba4f17cbe1215715cd6c8b6d48da6dde0b2095e 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -749,11 +749,11 @@ int p2m_alloc_table(struct p2m_domain *p2m)
  * hvm fixme: when adding support for pvh non-hardware domains, this path must
  * cleanup any foreign p2m types (release refcnts on them).
  */
-void p2m_teardown(struct p2m_domain *p2m)
+void p2m_teardown(struct p2m_domain *p2m, bool remove_root)
 /* Return all the p2m pages to Xen.
  * We know we don't have any extra mappings to these pages */
 {
-    struct page_info *pg;
+    struct page_info *pg, *root_pg = NULL;
     struct domain *d;
 
     if (p2m == NULL)
@@ -763,10 +763,22 @@ void p2m_teardown(struct p2m_domain *p2m)
 
     p2m_lock(p2m);
     ASSERT(atomic_read(&d->shr_pages) == 0);
-    p2m->phys_table = pagetable_null();
+
+    if ( remove_root )
+        p2m->phys_table = pagetable_null();
+    else if ( !pagetable_is_null(p2m->phys_table) )
+    {
+        root_pg = pagetable_get_page(p2m->phys_table);
+        clear_domain_page(pagetable_get_mfn(p2m->phys_table));
+    }
 
     while ( (pg = page_list_remove_head(&p2m->pages)) )
-        d->arch.paging.free_page(d, pg);
+        if ( pg != root_pg )
+            d->arch.paging.free_page(d, pg);
+
+    if ( root_pg )
+        page_list_add(root_pg, &p2m->pages);
+
     p2m_unlock(p2m);
 }
 

diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 8c1b041f71358e4528a2576a21a33103b510b500..8c5baba9544d3b1f99c2272a6c0bcdb908164526 100644 (file)
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -2701,7 +2701,7 @@ int shadow_enable(struct domain *d, u32 mode)
     paging_unlock(d);
  out_unlocked:
     if ( rv != 0 && !pagetable_is_null(p2m_get_pagetable(p2m)) )
-        p2m_teardown(p2m);
+        p2m_teardown(p2m, true);
     if ( rv != 0 && pg != NULL )
     {
         pg->count_info &= ~PGC_count_mask;
@@ -2866,7 +2866,7 @@ void shadow_final_teardown(struct domain *d)
         shadow_teardown(d, NULL);
 
     /* It is now safe to pull down the p2m map. */
-    p2m_teardown(p2m_get_hostp2m(d));
+    p2m_teardown(p2m_get_hostp2m(d), true);
     /* Free any shadow memory that the p2m teardown released */
     paging_lock(d);
     shadow_set_allocation(d, 0, NULL);

diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index f2af7a746ceda945d0375d573cd87b66539f62c5..c3c16748e7d501f32b02472662154f3516c7fb1c 100644 (file)
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -574,7 +574,7 @@ int p2m_init(struct domain *d);
 int p2m_alloc_table(struct p2m_domain *p2m);
 
 /* Return all the p2m resources to Xen. */
-void p2m_teardown(struct p2m_domain *p2m);
+void p2m_teardown(struct p2m_domain *p2m, bool remove_root);
 void p2m_final_teardown(struct domain *d);
 
 /* Add a page to a domain's p2m table */