[xen stable-4.16] x86/p2m: add option to skip root pagetable removal in p2m_teardown()

[patchbot@xxxxxxx]

commit 8fc19c143b8aa563077f3d5c46fcc0a54dc04f35
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Oct 11 14:52:39 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 11 14:52:39 2022 +0200

    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@xxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
    master commit: 1df52a270225527ae27bfa2fc40347bf93b78357
    master date: 2022-10-11 14:21:23 +0200
---
 xen/arch/x86/mm/hap/hap.c       |  6 +++---
 xen/arch/x86/mm/p2m.c           | 20 ++++++++++++++++----
 xen/arch/x86/mm/shadow/common.c |  4 ++--
 xen/include/asm-x86/p2m.h       |  2 +-
 4 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 47a7487fa7..a8f5a19da9 100644
--- 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 def1695cf0..aba4f17cbe 100644
--- 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 8c1b041f71..8c5baba954 100644
--- 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 f2af7a746c..c3c16748e7 100644
--- 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 */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16